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Molecular Nanomagnets: Syntheses and Characterization of High Nuclearity Transition Metal Complexes

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Molecular Nanomagnets: Syntheses and Characterization of High Nuclearity Transition Metal Complexes
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FOGUET-ALBIOL, MARIA D. ( Author, Primary )
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2008

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Magnetic fields ( jstor )
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University of Florida
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University of Florida
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Copyright Maria D. Foguet-Albiol. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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12/31/2011
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MOLECULAR NANOMAGNETS: SYNTHESES AND CHARACTERIZATION OF HIGH NUCLEARITY TRANSI TION METAL COMPLEXES By MARIA D. FOGUET-ALBIOL A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2006

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Copyright 2006 by Maria D. Foguet-Albiol

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To my family, for their love and support, and especially to Rosa.

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iv ACKNOWLEDGMENTS First and foremost, I would like to thank my research advisor, Professor George Christou. His constant guidance and support a llowed me to pursue my doctoral degree and express my own vision in research. I w ould also like to thank my other committee members (Dr. Daniel Talham, Dr. David Powell, Dr. Lisa McElwee-White, and Dr. Stephen Hill) who by their remarks, questions, an d interest in my research made me grow as a person and as a chemist. In addition, I wish to thank the following organizations: The Chemistry Department at University of Florida and The National Science Foundation (NSF) for their support in developing the projects. I would like to thank and acknowledge the individual students, scientists, and professors with whom I have collabor ated during my doctoral studies. These collaborators include Dr. Wo lfgang Wernsdorfer, who provi ded necessary single crystal measurements below 1.8 K on numerous com pounds; the crystallographers, Dr. Khalil Abboud and his staff at University of Fl orida Center for X-Ray Crystallography (UFCXC); Dr. Hans Gdel, Dr. Andreas Si eber and Dr. Olivier Waldman for their Inelastic Neutron Scattering measurements (INS) on two Mn4 samples, Dr. Steve Hill and Dr. John Lee in the UF Physics Depart ment for their High Frequency Electron Paramagnetic Resonance (HFEPR) measurements on the Fe7 complexes; and Dr. Naresh Dalal, and Dr. Micah North for their teamwork in Raman studies on single crystals of Mn4 clusters. I would like to e xpress my appreciation to th e entire Christou group, past and present, for their thoughtfu l discussions about chemistry or any other matters, and for

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v their companionship. Special thanks go to Dr. Abhudaya Mishra, for their frank friendship along these years. Finally, and most importantly, I would lik e to acknowledge the love and support of my family: my parents, Josep and Tonica; a nd my sisters and brothe rs (Fran, Rosa, Manel and Josep), who have always been there for me in every way. Also, special mention goes to the new "additions" to the family, those li ttle people who with their radiant pictures made me smile (Eva, Ines, Didac, Sofia and Olga). This journey would not have been possible without all of my friends over the y ears (especially Ivan, Rosa and Toni). These people told me things as they were, and st uck with me through thick and thin. I am grateful to all of them, as they contribute d to my journey through life. Their ideas and writings have greatly expanded my views of wh o we are, why we are here, what our work is, and why things are as they are.

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vi TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES...............................................................................................................x LIST OF FIGURES.........................................................................................................xiii ABBREVIATIONS.........................................................................................................xix ABSTRACT.......................................................................................................................xx CHAPTER 1 GENERAL INTRODUCTION................................................................................1 2 NEW Mn4 AND Mn12 SINGLE-MOLECULE MAGNETS, AND COMPUTATIONAL RATIONALIZATION OF THE OBSERVED GROUND STATE SPIN VALUES.......................................................................11 2.1 Introduction......................................................................................................11 2.2 Experimental Section.......................................................................................14 2.1.1 Syntheses...........................................................................................14 2.2.2 X-Ray Crystallography.....................................................................16 2.2.3 Computational Studies......................................................................18 2.3 Results and Discussion....................................................................................19 2.3.1 Syntheses...........................................................................................19 2.3.2 Description of the Structures............................................................21 2.3.2.1 Structure of [Mn12(O2CMe)14(mda)8] ( 1 )...........................21 2.3.2.2 Structure of [Mn4(O2CPh)4(mda)2(mdaH)2] ( 2 ).................24 2.3.2.3 Structure of [Mn6O2(OH)2(dpa)8(mdaH)2] ( 3 )...................26 2.3.3 Magnetochemistry of Complexes 1 , 2 and 3 ....................................29 2.3.3.1 Direct current magnetic studies of complexes 1 and 2 ......29 2.3.3.2 Alternating current magnetic susceptibility studies...........36 2.3.3.3 Magnetization vs dc field hysteresis loops........................39 2.3.4 Computational Studies......................................................................43 2.3.4.1 ZILSH and DFT calculations in complex 1 .......................44 2.3.4.2 ZILSH calculation and magnetic susceptibility fits for complex 2 ...........................................................................49 2.4 Conclusions......................................................................................................53

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vii 3 HIGH NUCLEARITY IRON AND NICKEL COMPLEXES: [Fe22O14(OH)3(O2CMe)21(mda)6](ClO4)2 AND [Ni24(O2CMe)42(mdaH)6(EtOH)6] INCORPORATING N-METHYLDIETHANOLAMINE (mdaH2)........................................................55 3.1 Introduction......................................................................................................55 3.2 Experimental....................................................................................................58 3.2.1 Syntheses...........................................................................................58 3.2.2 X-Ray Crystallography.....................................................................59 3.3 Results and Discussion....................................................................................62 3.3.1 Syntheses...........................................................................................62 3.3.2 Description of Structures..................................................................64 3.3.3 Magnetochemistry of Complexes 4 , 5 and 6 ....................................70 3.4 Conclusions......................................................................................................75 4 A NOVEL FAMILY OF Fe7 COMPLEXES WITH S = 5/2.................................77 4.1. Introduction.....................................................................................................77 4.2 Experimental....................................................................................................79 4.2.1 Syntheses...........................................................................................79 4.2.2 X-Ray Crystallography.....................................................................81 4.2.3 Single-Crystal, High-Frequency EPR Spectroscopy........................83 4.3 Results and Discussion....................................................................................83 4.3.1 Syntheses...........................................................................................83 4.3.2 Description of Structures..................................................................85 4.3.2.1 Structure of [Fe7NaO3(O2CPh)9(mda)3](ClO4) ( 7 )............85 4.3.2.2 Structure of [Fe7O3(O2CPh)9(mda)3(H2O)] ( 8 )..................86 4.3.2.3 Structure of [Fe7O3(O2CtBu)9(mda)3(H2O)3] ( 9 )...............88 4.3.3 Magnetochemistry of Complexes 7 , 8 and 9 ....................................89 4.3.3.1 Direct current magnetic studies of complexes 7 9 .............89 4.3.3.2 Alternating current magnetic susceptibility studies...........92 4.3.3.3 Magnetization vs dc field hysteresis loops........................94 4.3.4 Computational Methods....................................................................96 4.3.5 Single-Crystal, High-Frequency EPR (HFEPR) Spectroscopy of Complex 9 ..................................................................................99 4.4 Conclusions....................................................................................................104 5 MANGANESE COMPLEXES INCORPORATING AZIDES: ZERO, ONE AND TWO DIMENSIONAL STRUCTURES...................................................106 5.1 Introduction....................................................................................................106 5.2 Experimental Section.....................................................................................108 5.2.1 Syntheses.........................................................................................108 5.2.2 X-Ray Crystallography...................................................................111

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viii 5.3 Results and Discussion..................................................................................115 5.3.1 Syntheses.........................................................................................115 5.3.2 Description of Structures................................................................117 5.3.2.1 Structure of (HNEt3)[Mn7(mda)6Cl6] ( 10 ).......................117 5.3.2.2 Structure of {Na(HOMe)3[Mn7(mda)6(N3)6]}n ( 12 )........119 5.3.2.3 Structure of [Mn18O11(OH)(N3)12(tea)3(teaH)3(OMe)(HOMe)] ( 13 )...121 5.3.2.4 Structure of [Mn31O20(N3)4(O2CMe)23(tea)2(dea)2(OMe)6(MeOH)2]n ( 14 )...................................................................................124 5.3.3 Magnetochemistry of Complexes...................................................128 5.3.3.1 Direct current magnetic studies of complexes 10 14 .......128 5.3.3.2 Alternating current magnetic susceptibility studies.........134 5.3.3.3 Magnetization vs dc fi eld hysteresis loops of 13 .............136 5.4 Conclusions....................................................................................................138 6 EXCHANGE-BIASED DIMER: OPTIMIZATION OF THE MAGNETIC PROPERTIES AND FURTHER CHARACTERIZATION OF THE SYSTEM...............................................................................................140 6.1. Introduction...................................................................................................140 6.2 Experimental..................................................................................................142 6.2.1 Syntheses.........................................................................................142 6.2.2 X-ray Crystallography....................................................................145 6.3 Results and Discussion..................................................................................147 6.3.1 Syntheses.........................................................................................147 6.3.2 Description of Structures................................................................148 6.3.2.1 Structure of [Mn4O3Cl4(O2CEt)3(py)3]4MeCN ( 15 ).......149 6.3.2.2 Structure of [Mn4O3Cl4(O2CEt)3(d5-py)3]MeCN ( 16 )..152 6.3.2.3 Structure of [Mn4O3Cl4(O2CEt)3(py)3]C6H14 ( 17 )..........152 6.3.3 Magnetization studies.....................................................................153 6.3.3.1 Magnetization studies for complexes 15 20 ...................153 6.3.3.2 Magnetization vs dc field hys teresis loops for complex 15 .......................................................................158 6.3.3.3 Magnetization vs dc field hys teresis loops for complex 16 .......................................................................161 6.3.3.4 Magnetization vs dc field hysteresis loops for complex 17 .......................................................................161 6.3.3.5 Magnetization vs dc fiel d hysteresis loops for complexes 18 , 20 .............................................................164 6.4 Inelastic Neutron Scattering Spectroscopy....................................................166 6.4.1 Experimental Section......................................................................166 6.4.2 Results and Discussion...................................................................166 6.5. Raman Studies..............................................................................................175 6.6 Conclusions....................................................................................................181

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ix APPENDIX A BOND DISTANCES AND ANGLES.................................................................183 B LIST OF COMPOUNDS.....................................................................................220 C PHYSICAL MEASUREMENTS........................................................................221 D VAN VLECK EQ UATIONS...............................................................................226 LIST OF REFERENCES.................................................................................................229 BIOGRAPHICAL SKETCH...........................................................................................241

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x LIST OF TABLES Table page 2-1 Crystallographic data for complexes 1 , 2 and 3 .......................................................17 2-2 BVS calculations for the Mn atoms in complex 1 ...................................................23 2-3 BVS calculations for selected oxygen atoms in complex 1 .....................................24 2-4 BVS calculations for the Mn atoms in complex 2 ...................................................25 2-5 BVS calculations for selected oxygen atoms in complex 2 .....................................25 2-6 BVS calculations for the Mn atoms in complex 3 ...................................................28 2-7 BVS calculations for selected oxygen atoms in complex 3 .....................................28 2-8 Exchange constants computed for complex 1 and various model clusters with ZILSH and DFT methods.........................................................................................47 2-9 Magnetic exchange parameters fo r phenoxo bridging groups of binuclear MnIIMnIII complexes..............................................................................................49 3-1 Crystallographic data for comlexes 4 , 5 and 6 .........................................................61 4-1 Crystallographic data for comlexes 7 , 8 and 9 .........................................................82 4-2 BVS calculations for the Fe atoms in complex 7 .....................................................86 4-3 BVS calculations for the Fe atoms in complex 8 .....................................................87 4-4 BVS calculations for the Fe atoms in complex 9 .....................................................88 4-5 Exchange constants, spin couplings of the complexes 7 , 8 , and 9 ...........................98 4-6 Ground state spins, loca l z-components of spin, Mi, and energies (cm-1) of the first excited states for complexes 7 , 8 , and 9 found with ZILSH calculations.........99 5-1 Crystallographic data for complexes 10 , 12 , 13 and 14 .........................................114 5-2 BVS calculations for the Mn atoms in complex 10 ...............................................119

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xi 5-3 BVS calculations for the Mn atoms in complex 12 ...............................................121 5-4 BVS calculations for the Mn atoms in complex 13 ...............................................123 5-5 BVS calculations for selected oxygen atoms in complex 13 .................................124 5-6 BVS calculations for the Mn atoms in complex 14 ...............................................126 6-1 Crystallographic data for complexes 15 , 16 , and 17 ..............................................148 6-2 Comparison of selected intermolecu lar distances () and angles () for complexes 15 , 16 and 17 .......................................................................................152 6-3 Parameters obtained from fitting the 10 kG susceptibility data of complexes 15 20 .......................................................................................................................156 6-4 Parameters obtained from fitting the 10 kG susceptibility data of complexes 15-20 .......................................................................................................................158 6-5 Spin Hamiltonian parameters for th e deuterated and undeuterated [Mn4]2 dimer.172 6-6 ClCl distances and J values for the three different [Mn4]2 samples....................174 6-7 Assignment of Raman modes (cm-1) for [Mn4]2 following the DFT calculations results.....................................................................................................................176 6-8 Assignment of Raman modes (cm-1) for [Mn4]2 following one experimental approach.................................................................................................................177 6-9 Assignment of Raman modes (cm-1) for [Mn4]2 following a second experimental approach...........................................................................................179 6-10 Assignment of Raman and IR modes (cm-1) for [Mn4]2 predicted by DFT calculations.............................................................................................................180 A-1 Selected interatomic distances () and angles () for [Mn12(O2CMe)14(mda)8]MeCN ( 1 ) ( 1 MeCN).................................................183 A-2 Selected interatomic distances () and angles () for [Mn4(O2CPh)4(mda)2(mdaH)2]CH2Cl2Et2O ( 2 CH2Cl2Et2O).....................185 A-3 Selected interatomic distances () and angles () for [Mn6O2(OH)2(dpa)8(mdaH)2]MePh ( 3 MePh)..................................................186 A-4 Selected interatomic distances () and angles () for [Ni24(O2CMe)42(mdaH)6(EtOH)6]7H2OMeCO2HEtOHEt2O ( 4 H2O6MeCO2HEtOHEt2O)....................................................................187

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xii A-5 Selected interatomic distances () and angles () for [Ni(mdaH2)2](O2CMe)2 ( 5 )....................................................................................189 A-6 Selected interatomic distances () and angles () for [Fe22O14(OH)3(O2CMe)21(mda)6](ClO4)2H2O4EtOH4Et2O ( 6 H2O4EtOHEt2O)..........................................................................................190 A-7 Selected interatomic distances () and angles () for [Fe7NaO3(O2CPh)9(mda)3]ClO4Et2O ( 7 Et2O)..................................................196 A-8 Selected interatomic distances () and angles () for [Fe7O3(O2CPh)9(mda)3(H2O)] ( 8 )..........................................................................198 A-9 Selected interatomic distances () and angles () for [Fe7O3(O2CtBu)9(mda)3(H2O)3] ( 9 ).......................................................................199 A-10 Selected interatomic distances () and angles () for (HNEt3)[Mn7(mda)6(Cl)6]MeCNEt2O ( 10 MeCNEt2O).....................................200 A-11 Selected interatomic distances () and angles () for {Na(HOMe)3[Mn7(mda)6(N3)6]}n ( 11 )...................................................................202 A-12 Selected interatomic distances () and angles () for [Mn18O11(OH)(N3)12(tea)3(teaH)3(OMe)(HOMe)]CH2Cl2Et2O ( 12 CH2Cl2Et2O).................................................................................................204 A-13 Selected interatomic distances () and angles () for [Mn31O20(N3)4(O2CMe)23(tea)2(dea)2(OMe)7(MeOH)]nMeCN ( 13 MeCN).........................................................................................................210 A-14 Selected interatomic distances () and angles () for [Mn4O3Cl4(O2CEt)3(py)3]MeCN ( 14 MeCN)...................................................217 A-15 Selected interatomic distances ( ) and angles () for [Mn4O3Cl4(O2CEt)3(d5-py)3]MeCN ( 15 MeCN)..............................................218 A-16 Selected interatomic distances () and angles () for [Mn4O3Cl4(O2CEt)3(py)3]C6H14 ( 16 C6H14)..........................................................219

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xiii LIST OF FIGURES Figure page 1-1 Types of magnetic materials dependi ng on the nature of the interaction...................3 1-2 Magnetization vs field hyst eresis loop for a magnet..................................................4 1-3 Representative plot of the energy barr ier vs the angle of the magnetization from the easy axis, and representation of th e energy barrier vs the magnetization direction vector in the abse nce of the magnetic field.................................................7 1-4 Representation of the spin projection of the ms states in a 3-D spherical fashion.....7 1-5 Typical frequency-dependent out-of-pha se ac magnetic susceptibility plot and magnetization vs field hyster esis loop for an SMM...................................................8 1-6 Schematic representation of the double-well potential for S = 10 at H = 0, thermally assisted tunneling and pure quantum tunneling, and at H 0, thermally activated relaxation a nd resonant quantum tunneling................................9 2-1 ORTEP representation in PovRay format of complex 1 , front view.......................22 2-2 ORTEP representation in PovRay format of complex 1 , side view.........................22 2-3 ORTEP representation in PovRay format of complex 2 ..........................................25 2-4 ORTEP representation in PovRay format of complex 3 , front view.......................27 2-5 ORTEP representation in PovRay format of complex 3 , side view.........................27 2-6 Plot of MT vs temperature of complexes 1 and 2 ....................................................30 2-7 Plot of MT vs temperature of complex 3 . The inset plot is the in-phase ac susceptibility, plotted as M T vs T ...........................................................................31 2-8 Plot of the fitting of MT vs temperature of complex 2 ............................................33 2-9 Plot of reduced magnetization M / N B vs H / T of complexes 1 and 2 .......................34 2-10 Two-dimensional contour plot of the error surface for the D vs g fit for complexes 1 and 2 ....................................................................................................35

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xiv 2-11 Plot of the in-phase (as M' T ) and out-of-phase ( M'') ac susceptibility signals vs temperature of complex 1 and 2 ..........................................................................38 2-12 Magnetization ( M ) vs magnetic field hysteresis loops for a singl e crystal of complex 1 .................................................................................................................41 2-13 Magnetization ( M ) vs magnetic field hysteresis loops for a singl e crystal of complex 2 ................................................................................................................42 2-14 Relaxation time vs temperature studies on a single crystal. Plot of relaxation time ( ) vs 1/ T for complexes 1 and 2 ......................................................................43 2-15 Depiction of the spin alignments in the S = 7 and S = 0 ground state of complex 1 .................................................................................................................48 2-16 Schematic diagram of metal framework for complex 2 ,..........................................50 2-17 Comparison of calculated and experi mental variable temperature magnetic susceptibility of complex 2 ......................................................................................51 2-18 Error in fit of variable temperat ure magnetic susceptibility of complex 2 versus Jbb..................................................................................................................53 3-1 ORTEP representation in P ovRay format of the complex 4 and its asymmetric unit: [Ni4(O2CMe)7(mdaH)(EtOH)].....................................................65 3-2 ORTEP representation in PovRay format of the asymmetric unit of complex 4 ; and its representation by polyhedra.......................................................66 3-3 ORTEP representation in PovRay format of complex 5 ..........................................67 3-4 ORTEP representation in PovRay format of complex 6 ..........................................68 3-5 ORTEP representation in PovRay fo rmat of the central unit of complex 6 .............68 3-6 ORTEP representation in PovRay fo rmat of the side unit of complex 6 .................69 3-7 Plot of MT vs temperature of complex 4 .................................................................71 3-8 Plot of reduced magnetization M / N B vs H / T for a dried, microcrystalline sample of complex 4 ................................................................................................72 3-9 Two-dimensional contour plot of the error surface for the D vs g fit and threedimensional mesh plot error vs g vs D for the same fit for complex 4 ....................72 3-10 Plot of MT vs T for complex 5 . eff vs T as inset plot and plot of 1/ M vs T for 5 . Inset: the solid line represents a fit to the Curie–Weiss law....................................73 3-11 Plot of MT vs temperature of complex 6 .................................................................74

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xv 3-12 Plot of the in-phase (as M T ) ac susceptibility signals vs temperature of complex 4 in eicosane at the indica ted oscillating frequencies................................75 4-1 ORTEP representation in PovRay format of complex 7 and its core.......................85 4-2 ORTEP representation in PovRay format of complex 8 and its core.......................87 4-3 ORTEP representation in PovRay format of complex 9 ..........................................88 4-4 Plot of MT vs T for complexes 7 , 8 and 9 . The inset is a eff vs T plot...................89 4-5 Plot of M / N B vs H / T for dried samples of complex 7 , 8 , and 9 .............................90 4-6 Two-dimensional contour plot of the error surface for the D vs g fit and three-dimensional mesh plot error vs g vs D for complex 7 ....................................91 4-7 Two-dimensional contour plot of the error surface for the D vs g fit and three-dimensional mesh plot error vs g vs D for complex 8 ....................................92 4-8 Two-dimensional contour plot of the error surface for the D vs g fit for complex 9 and three-dimensional mesh plot error vs g vs D for complex 9 ............92 4-9 Plot of the in-phase and out-of-phase ac susceptibility signals vs temperature of complexes 7 , 8 and 9 ............................................................................................93 4-10 Magnetization ( M ) vs magnetic field hysteresis loops for a single crystal of complex 9 .............................................................................................................95 4-11 Schematic diagram of complexes, including numbering scheme used in ZILSH calculations, and spin alignments found for the ground state of all three complexes........................................................................................................97 4-12 HFEPR spectra of the crystal taken at 51.8 GHz, at temperatures from 2.0 to 15.0 K. Inset is the simulated Zeeman energy diagram in the hard-plane.........101 4-13 Plot of the HFEPR peak positions from angle-dependent measurements at 51.8 GHz and 179.8 GHz.......................................................................................102 4-14 Energy difference diagrams cons tructed from frequency-dependent measurements of both the easy-axis and hard-plane..............................................103 5-1 Representation of the two typica l coordination mode s of the azide (N3-) bridging ligand.......................................................................................................107 5-2 ORTEP representation in PovRay format of the anion of complex 10 and its representation by polyhedra........................................................................118 5-3 ORTEP representation in PovRay format of the anion of complex 10 and 11 ......119

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xvi 5-4 ORTEP representation in PovRay format of complex 12 ......................................120 5-5 ORTEP representation in PovRay format of complex 13 and its core...................122 5-6 A labeled ORTEP representation in PovRay fo rmat of the different layers of complex 13 .........................................................................................................123 5-7 ORTEP representation in PovRay format of the Mn31 repeating unit of complex 14 .............................................................................................................125 5-8 ORTEP representation in PovRay fo rmat showing the bending of the Mn31 unit of complex 14 ..................................................................................................127 5-9 An stick representation of 14 along the b axis, and along the c axis.....................127 5-10 Plot of MT vs temperature of complex 10 .............................................................128 5-11 Plot of reduced magnetization M / N B vs H / T of complex 10 ................................129 5-12 Plot of MT vs temperature for a dried, microcrystalline sample of complex 13 in eicosane, measured in a 1.0 kG field.............................................................131 5-13 Plot of MT vs temperature of complex 14 . The inset plot is the in-phase ac susceptibility......................................................................................................131 5-14 Plot of reduced magnetization M / N B vs H / T of complex 13 ................................132 5-15 Plots of the error surf ace for the error vs D vs g fit for complex 13 ......................133 5-16 Plot of the in-phase and out-of-phase ac susceptibility signals vs temperature of complex 10 .............................................................................................................134 5-17 Plot of the in-phase and out-of-phase ac susceptibility signals vs temperature of complex 13 .............................................................................................................135 5-18 Magnetization ( M ) vs magnetic field hysteresis loops fo r a single crystal of complex 13 .........................................................................................................136 5-19 Relaxation time vs temperature studies on a single crystal. Magnetization vs time decay plots at the indicated temper atures and Arrhenius plot using the resulting relaxation time ( ) vs T data for complex 13 ...........................................137 6-1 ORTEP representation of complex 15 ...................................................................149 6-2 ORTEP representation of the [Mn4]2 dimer of [Mn4O3Cl4(O2CEt)3(py)3]............150 6-3 ORTEP representation of two dimers....................................................................151 6-4 Plot of MT vs temperature of complexes 15-20 ....................................................154

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xvii 6-5 Plots of fitting of MT vs temperature of complexes 15-20 ....................................156 6-6 Plot of reduced magnetization M / N B vs H / T of complexes 18 , 19 and 20 ...........157 6-7 Hysteresis loops measured along Hz in the presence of a constant transverse field varying the temperature from 1.0 K to 0.04 Kand along Hz in the presence of a constant temperature varying th e scan rate from 0.140 T/s to 0.004 T/s loops measured along Hz in the presence of a constant transverse field................158 6-8 Hysteresis loops measured along Hz at a temperature of 0.04 K and a scan rate of 0.140 T/s............................................................................................................159 6-9 Hysteresis loops measured along Hz from -1.2 T to 1.2 T at a temperature of 0.04 K and 0.004, 0.017 and 0.140 T/s scan rate s and derivative plot of the hysteresis loop at 0.04 K and at different field sweep rates...................................160 6-10 Hysteresis loops of complex 17 .............................................................................162 6-11 Hysteresis loops at 0.04 K and 0.008 T/s of complex 15 and 17 ...........................163 6-12 Hysteresis loops of 17 at 0.04 K and variable scan rates and the derivative plot in identical conditions.....................................................................................163 6-13 Hysteresis loops for 18 measured along Hz in the presence of a constant transverse field varying the temper ature from 1.0 K to 0.04 K and along Hz in the presence of a constant temperatur e varying the scan rate from 0.280 T/s to 0.001 T/s.............................................................................................................164 6-14 Hysteresis loops on 20 measured along Hz in the presence of a constant transverse field varying the temp erature from 1.0 K to 0.04 Kand along Hz in the presence of a constant temperature varying the scan rate from 0.560 T/s to 0.001 T/s.................................................................................................................164 6-15 A comparison of the hysteresis loops at 0.04 K and 0.004 T/s of complexes 15 , 17 , 18 and 20 ....................................................................................................165 6-16 Energy level diagram of an axially anisotropy split S = 9/ 2 ground state and a [Mn4]2 dimer with antiferromagnetic coupling...................................................168 6-17 INS spectra at 6.1 K and 19.4 K of complex 15 , after background subtraction in the energy gain side and in the energy loss side................................................169 6-18 INS spectra at 1.5 K, 3.2 K and 19.2 K of complex 16 before and after substraction.............................................................................................................170 6-19 The Raman modes of [Mn4]2..................................................................................176

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xviii 6-20 Comparison of the Raman spectra of model compounds to that of [ Mn4]2 at 295 K..................................................................................................................177 6-21 Spectral comparison of the monomers Mn4-Pr and Mn4-Ac with that of the dimer [Mn4]2...........................................................................................................178 6-22 Typical IR spectrum of the SMM [Mn4]2 and a comparison of Raman and IR spectra................................................................................................................180

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xix ABBREVIATIONS MeCN acetonitrile BVS bond valence sum CH2Cl2 dichloromethane DFT density f unctional theory Et ethyl J exchange-coupling constant G gauss HFEPR high-frequency electron paramagnetic resonance INS inelastic neutron scattering IR infrared JT Jahn-Teller MeOH methanol Me methyl CH2Cl2 methylene chloride Ph phenyl KBr potassium bromide ORTEP oak ridge thermal ellipsoid plotting program QTM quantum tunneling of magnetization SQUID superconducting quantum interference device SMM single-molecule magnet TIP temperature-independent paramagnetism But tertiary butyl T tesla

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xx Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy MOLECULAR NANOMAGNETS: SYNTHESES AND CHARACTERIZATION OF HIGH NUCLEARITY TRANSI TION METAL COMPLEXES By Maria D. Foguet-Albiol December 2006 Chair: George Christou Major Department: Chemistry High nuclearity transition metal complexes have attracted a lot of attention because of their aesthetically pleasant structures and/ or their potential applications. The fusion of the world of magnetism with th e exciting research in physic s and chemistry led to the realization of interesting t ypes of materials that can f unction as nanoscale magnetic particles. The study of the magnetism of inor ganic complexes and especially the study of these molecular nanomagnets (or single-molecule magnets, SMMs) is a field that has generated intense interest in the scientific community. Interest in these molecular nanomagnets arises as part of a broa der investigation of nanomagnetism (and nanotechnology), as these represent the ulti mate step in device miniaturization. The primary purpose of this dissertation is the development of new synthetic methods intended for the preparation of novel single-molecule magnets (SMMs). The definition of the "bottom-up approach" is to increase the size of molecules by adding new magnetic centers; this is attractive but does not actually reflect how the chemistry takes

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xxi place. Various strategies have been employe d in developing the aforementioned synthetic methods which include the use of mononuclear as well as preformed clusters as starting materials; and the introducti on of new alcohol based ligands as N-methyldiethanolamine (mdaH2) and triethanolamine (teaH3), since currently only a few alcohol based ligands have been used by different research groups . Many of these efforts have led to the isolation of new polynuclear Mn clusters with nuclearities ranging all the way from four to thirty-one. Additionall y, a family of related Fe7 complexes has been synthesized. The transition metal cluster chemistry has also been extended to nickel-containing species. Many of these polynulear tran sition metal complexes func tion as single-molecule magnets. An additional research direction discussed herein is the study of the exchangecoupled dimer of single-molecule magne ts (SMMs) by previously unemployed techniques (i.e., inelastic neut ron scattering (INS)). This latt er study resulted in a better understanding of the effects of chemical and physical variations on the magnetic parameters S , D and J . These studies provide insight into approaches necessary to gain access to clusters that behave as single-m olecule magnets at more technologically relevant temperatures, an issue of growing concern as the research area further matures.

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1 CHAPTER 1 GENERAL INTRODUCTION In the last two decades, the prefix "na no" has been used extensively. From the lecture given by Richard Feynman at an Am erican Physical Society meeting in 1959 (which many consider the first talk on na notechnology), to Eric Drexler who coined the term and promoted the significance of "nanoscale" through lectures and books, the term has acquired its current sense. Nanoscien ce and nanotechnology describe the study of phenomena and manipulation of materials at the nanoscale, leading to an understanding and control of nanostructures, and pertain broadly to fiel ds such as biology, physics, chemistry, or any existing research ar ea relevant to the nanoscale. Although nanotechnology deals with everythi ng that is small (typically 10-9 m and beyond), this is not the case with grants associated with th is burgeoning field. It has become such an appealing field that the funding of proj ects has grown from 464 million in 2001 to estimates of 1.1 billion dollars for 2006.1 However, not all researchers use the te rm in the proper context, as is well documented in the book "Nano-hype: the tr uth behind the nanotechnology buzz".2 Some of the "nano" propaganda is just a means of making money, gaini ng publicity, obtaining research grants, and satisfying university budgets. Nevertheless, in the case of nanomagnetism, it is different, because the fundamental properties of magnets are defined at a nanometer length scale. Interest in molecular nanomagnets arises as part of a broade r investigation of nanomagnetism (and nanotechnology), as these represent the ultimate step in device

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2 miniaturization. Molecular nanomagnets ar e polynuclear metal complexes containing transition metal ions, with a large but fi nite number of magnetic centers surrounded by shells of organic ligands. The study of the magnetism of these complexes, better known as single-molecule magnets (SMMs), is a field that has generated intense interest in the scientific community, because the study of th ese species is relevant to theories of quantum chemical phenomena and to potenti al technological app lications. This is because single-molecule magnets (SMMs) display magnetic properties that are intermediate between isolated paramagnets and bulk magnetic materials. Magnetism is an effect generated in ma tter by the motion of electrons within its atoms. As all matter is made up of atoms that contain one or more electrons, matter is expected to be magnetic. But in most matte r, electrons pair up with opposite magnetic moments and thus there is no net magnetic moment. These substances are called diamagnetic and they are very weakly repelled by a magnetic field. However, in many species, it is not possible to pa ir up all the electrons, and a molecule of such a substance will have a magnetic moment. In most substanc es with unpaired electrons, the individual magnetic moments are randomly oriented and although these materials are attracted to a magnetic field, the attraction is weak: these materials are said to be paramagnetic. In some substances, the individual magnetic moments (spins, symbolized by arrows, ) interact so that all the unpaired electrons align in the same di rection: such species are said to be ferromagnetic ( ). In contrast, some material s contain unpaired electrons interacting in such a way that the spins ali gn in an antiparallel fa shion (i.e., pointing in opposite directions): these materials are called antiferromagnets, if th e individual spins all have the same magnitude and there is no net magnetic moment ( ), or ferrimagnets, if

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3 the interacting spins have different magn itudes and thus a net magnetic moment ( ) (Figure 1-1). ParamagneticFerromagneticAntiferromagnetic Ferrimagnetic Figure 1-1. Types of magnetic materials de pending on the nature of the interaction Ferriand ferromagnets are organized in ma gnetic domains, regions of material in which all the spins are aligned to give a ne t magnetization. These substances are strongly attracted to a magnetic field because each dom ain rotates to align itself with the field. There is a temperature, known as th e Curie temperature or Curie point (Tc), above which the thermal energy causes the domain s to lose their parallel alignment, and consequently ferro/ferrimagnetic material s become paramagnetic. Antiferromagnets, conversely, are the result of spin pairing anti-paralle l and producing zero net magnetization below the Nel Temperature, TN. Since antiferromagnets and paramagnets give a total net spin of zero, magnets can only be built from either ferromagnets or ferrimagnets, where a net magnetization is present. In large pieces of ferromagnets or ferr imagnets, despite the nature of the interactions, the most thermodynamically (ent ropically) favored situation is when the magnetization of the system is minimized (i.e ., when the net magnetization is zero). This is the origin of domain formation. Differe nt domains within a particle of magnetic material have their net magnetization vector randomly oriented, re sulting in an overall magnetization of zero for the particle. To align the magnetization in the different domains, a strong magnetic field must be appl ied to overcome the energy barrier to break

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4 the domain walls and form a particle with a single domain. In some cases, the fieldinduced magnetization does not decay when the field is removed, and it is this remnant magnetization that directly gives useful ma gnetic properties to some materials. If a situation is reached where a ll the spins are parallel, and no domains are present, the sample will remain in that situation (below Tc) until enough energy is given to the system to overcome the energy barrier to domain fo rmation. Because an additional field is required to reverse the direct ion of the magnetization, magnetic storage of information is possible in particles of ferromagnetic or fe rrimagnetic materials. This behavior is observed in the classical hysteresis be havior of magnets (Figure 1-2). Figure 1-2. Magnetization vs. fiel d hysteresis loop for a magnet Because all information technologies seek to reduce the size of the magnetic memory elements, to achieve the storage of greater quantities of digital information on smaller surface areas, the need to develop magn etic particles of nanoscale dimensions is unavoidable. One approach towards this end involves the fr agmentation of bulk ferromagnets or ferrimagnets. For example, fr agments of magnetite can be broken down such that each fragment is smaller in si ze than a single domain (20 to 200 nm); these nanoscale magnetic particles are known as supe rparamagnets. Superparamagnets are still magnets and within them all spins ar e aligned due to short-range ordering. Superparamagnets are single-domain particles and thus have no domain formation-related

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5 remnant magnetization, but instead possess magne tic anisotropy (due to the identity of the metal ion and the shape of the particle) that determines the energy barrier to be overcome in the process of reorientation of the magnetization, resul ting in slow magnetic relaxation. Most superparamagnets are obtained from fragmentation of bulk materials such as metal oxides. This results in particles with a distribution of sizes, sh apes and defects. The presence of particle size and shape distribution leads to a di stribution of relaxation times which complicates the study of their magnetic properties. Another approach called the "bottom-up appr oach", is based on the syntheses of molecule-based magnets. In 1966, it was discovered that the compound chlorobis(diethyldithiocarbamato)i ron(III) behaved as a fe rromagnet at extremely low temperatures due to intermolecular interactions.3 Since then, chemists have realized that it is possible to achieve a variety of such magnetic materials starting from paramagnetic molecular units. Molecule-based magnets are 1, 2-, or 3-D lattices of molecular building blocks, which are synthesized from single mo lecules and selected bridging groups. They have long-range interactions and form do mains, and so they behave as magnets. Advantages of this approach include lo w density, low temperature processability, solubility, and others.4 A big breakthrough in molecule-based sy stems was the discovery that a single molecule can function as a nanoscale ma gnet by itself and without any long-range ordering.5, 6, 7 Such molecules were called single-mo lecule magnets (SMMs). In order to be a SMM, a molecule must possess a la rge ground state spin and negative magnetic anisotropy (gauged by the zero-field splitting (ZFS) parameter D), (i.e., Ising or easy-

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6 axis-type anisotropy). SMMs are thus individu al molecules that can function as magnets below a certain blocking temperature, TB. They exhibit superparamagnet-like slow rates of magnetization reorientation, which result in magnetization vs. field hysteresis, as expected for any magnet below TB. As a result of magnetic bistability, they can potentially be used in high-density information storage devices.8, 9 The first molecule to show this behavior was [Mn12O12(O2CMe)16(H2O)4], with a ground state spin of S = 10; this molecule behaves as a magnet, but the magnetic properties are intrinsic to the molecule, and not due to interactions between molecules. To verify the latter hypothesis, magnetic studies of this compound diluted in a diamagnetic polyethylene matrix or dissolved in an organic solvent were performed.10 The results confirmed the absence of threedimensional long-range magnetic interactions. For Hz = 0, the magnetic energy levels are labeled by the quantum number ms (– S Ms S , where S = total spin), which represents the projection of S onto the easy axis. The combination of negative easy-axis type magne tic molecular anisotropy along with a large ground state spin, results in a split ting of the ground state spin into 2 S +1 sublevels. The fact that the magnetic anisotropy is negative makes the larger |ms| states be lower in energy. Therefore, the magnitude of the energy barrier ( U ) separating the spin 'up' and 'down' states is S2|D| for integer spin values or ( S2 1/4)|D| for half-integer spin values. Figure 3-1 shows the plot of the ms sublevels as a function of the angle of the magnetization from the easy axis and energy barrier vs . the magnetization direction, for a Mn12 complex with an S = 10 experiencing zero-field splitting.

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7 Directions of the magnetization vector ms= -10 = 10 -9 -5 -8 -4 -7 -3 -6 0 -2 -1 7 6 5 8 9 2 1 4 3 Angle ( )Energyb) Energy 100|D| ms= 0 ms= +10 +9 +8 +7 +6 +5 +4 +3 +2 ms= -10 -9 -8 -7 -6 -5 -4 -3 -2 +1 -1a)Angle ( ) ms UDirections of the magnetization vector ms= -10 = 10 -9 -5 -8 -4 -7 -3 -6 0 -2 -1 7 6 5 8 9 2 1 4 3 Angle ( )Energyb) Energy 100|D| ms= 0 ms= +10 +9 +8 +7 +6 +5 +4 +3 +2 ms= -10 -9 -8 -7 -6 -5 -4 -3 -2 +1 -1a)Angle ( ) ms U Figure 1-3. Representative plots of the energy barrier vs. (a) the angle of the magnetization from the easy axis, and (b ) energy barrier vs. the magnetization direction vector in the ab sence of the magnetic field Another means used by chemists and physicis ts in the molecular magnetism area to represent the quantized precessing projection of the magnetization vector is shown in Figure 1-4. Figure 1-4. Representation of th e spin projection of the Ms states in a 3-D spherical fashion Due to this energy barrier ( U ), SMMs show slow relaxation of the magnetization: in order to reverse the spin (i.e., from 'up' to 'down'), the molecule has to overcome the thermal energy barrier ( U ). This behavior can be experimentally observed by the appearance of frequency-de pendent signals in the out-of-phase AC magnetic susceptibility studies, in conjunction with hysteresis loops in the magnetization vs. applied dc field scans (Figure 1-5).

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8 a) b) a) b) Figure 1-5. Typical frequency-dependent out-o f-phase AC magnetic susceptibility plot (a) and magnetization vs. field hysteresis loop (b) for an SMM Owing to their sub-nanoscale dimensions, as well as monodisperse character, SMMs straddle the quantum and classical desc riptions of magnetism. The phenomena of quantum tunneling of the magnetization (QTM)11 and quantum phase interference12 have been observed in SMMs. An alternative path way for the relaxation of the magnetization in a SMM between degenerate Ms levels (in zero applie d field) involves tunneling through the energy barrier. In the presence of an applied field, the symmetric potential energy barrier becomes asymmetric; one orientation of the magnetization (parallel to the applied field) is favored over the others. Thus, a field is applied, the degeneracy of the Ms states is lost. In the absence of a magnetic field and when the t unneling process involves the ground state spin (lowest lying Ms levels of the S manifold), the process is called pure quantum tunneling, or ground state quantum tunneling (Figure 1-6a ). When this tunneling involves higher energy Ms states, it is referred to as thermally -assisted quantum tunneling (TAQT). At certain values of the external field (when an Ms state on one side of the well matches in energy with an Ms' state on the other side of the we ll), the magnetization can again tunnel through the barrier (Figure 16b), when the tunneling pro cess involves the ground state

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9 Ms level (Ms = 10) tunneling to a lower -Ms level, the tunne ling process is called resonant quantum tunneling (Figure 1-6 b). a) b) a) b) Figure 1-6. Schematic representation of the double-well potential for S = 10 showing (a) at H = 0, thermally assisted tunneling and pure quantum tunneling, and (b) at H 0, thermally activated relaxati on and resonant quantum tunneling In contrast to the hysteresis loops of tr aditional ferrior fe rromagnetic materials, the plots of magnetization vs. applied magnetic field of SMMs show steps that occur at regular intervals. The observed steps corres pond to an increase in th e relaxation rate of magnetization that occurs when quantum t unneling of the magnetization takes place. Additionally, QTM in the ground state can be observed as a temperature-independent relaxation rate at low enough temperatures , as has been observed for several SMMs.13, 14 There has been great interest for over a decade in understanding this new magnetic phenomenon of single-molecule magnetism, an d in finding other compounds that exhibit similar properties. Since then, ot her oxidation levels of the [Mn12] family,15, 16 and other Mnx and Mx (M = Fe, V, Ni) SMMs have been prepared with a range of S values, both integer and half-integer.17 Furthermore, an interesting example is the first exchangecoupled dimer of SMMs, [Mn4O3Cl4(O2CEt)3(py)3], which has demonstrated the feasibility of fine-tuning the quantum propert ies of these nanoscale magnetic materials.18 The complexes presented in this disserta tion exhibit various magnetic properties, from paramagnetism to ferromagnetism. Si ngle-molecule magnets (SMMs) display

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10 magnetic properties which are intermediate between isolated paramagnets and bulk magnetic materials. They display slow magne tization relaxation, hyste resis effects, and phenomena that have implications for f undamental science and potential future applications (i.e., qubits in quantum computers) . The main objective in this research area is to prepare a SMM that behaves as a magne t at technologically relevant temperatures (i.e., at least 77 K). For this purpose, different approaches have been undertaken: the preparation of novel 3d metal complexes posse ssing differing topologies that may behave as SMMs and the addition of new derivatives to an already existing family of SMMs so that structural features may be correlate d with magnetic properties and ultimately, a rational optimization for improved SMMs may be developed. The work herein highlights the preparation of novel 3d metal complexes by using alcohol-based ligands with a central nitr ogen atom: N-methyldiethanolamine (mdaH2) and triethanolamine (teaH3). These ligands have been used previously in inorganic chemistry, and there are a few examples of polynuclear complexes. However, the magnetic properties of these complexes with paramagnetic metal ions were unexplored. Thus, the use of mdaH2 and teaH3 with various transition metals has afforded complexes of varying nuclearity, topology, and peripheral ligation. Some of these complexes behave as SMMs and have been studied by a variet y of physical methods, and spectroscopic techniques.

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11 CHAPTER 2 NEW Mn4 AND Mn12 SINGLE-MOLECULE MAGNETS, AND COMPUTATIONAL RATIONALIZATION OF THE OBSERVED GROUND STATE SPIN VALUES 2.1 Introduction Single-molecule magnets (SMMs) represent a molecular or "bottom-up" approach to nanoscale magnetic materials. Such molecules display the superparamagnetic properties normally associated with much larger magnetic particles, and they can therefore function as magnets below their blocking temperature, TB.5, 6, 7 Being molecular, SMMs differ fundamentally from traditional or "top-down" nanoscale magnets composed of metals, metal alloys, me tal oxides, and similar. Indeed, they bring to nanomagnetism all the advantages of mol ecular chemistry, including monodispersity, crystallinity, true sol ubility (rather than collo id formation), a shell of organic groups that prevents close contact of a molecule’s magnetic core with those of neighboring molecules, and the ability to vary this orga nic shell at will using standard chemical methods. SMMs derive their properties from a comb ination of a large ground state spin ( S ) value and a significant magnetoanisotropy of the Ising (easy-axis) type. As a result, SMMs possess a barrier to magnetization relaxation ( U ) whose upper limit is given by S2|D| and ( S2-)|D| for integer and half-integer S values, respectively. At low enough temperatures, where this ba rrier is significant vs. k T , SMMs display out-of-phase ac magnetic susceptibility ( M'') signals, and hysteresis in ma gnetization vs. applied dc field loops, the latter bei ng the diagnostic pr operty of a magnet.19, 20

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12 SMMs have been proposed for several poten tial applications, such as very highdensity information storage, where each b it of information would be stored as the magnetization orientation of a single molecu le; and in quantum computing, where each molecule would function as a quantum bit (qubi t) owing to the fact that it exhibits quantum tunneling of magnetization (QTM), also called magnetic quantum tunneling (MQT), through the anisotropy barrier to magnetization relaxation.21 The QTM thus allows the molecule to exist as a quantum s uperposition of states, a necessary property of a qubit. This latter potential application ar ises from the fact that SMMs straddle the classical/quantum interface, exhibiting both the classical properties of the macroscale, such as magnetization hysteresis, and the quant um properties of the atomic or microscale, such as QTM and also quantum phase interference (Berry phase).9, 22 Indeed, both properties are manifest in a single experiment, magnetization vs. dc field sweeps, where the resulting hysteresis loop, the classical propert y of a magnet, displays step-like features at periodic field va lues corresponding to those at wh ich levels on either side of the anisotropy barrier to relaxa tion are in resonance, and th e magnetization relaxation rate thus increases due to the onset of QTM. The number of identified SMMs has grown cons iderably in the last several years, and most of them have been in Mn chemis try, but there is still a need to expand the database of known examples and structural t ypes. Reasons for this include raising the blocking temperatures to higher values to ma ke potential applications more feasible, identifying SMMs with unusual structural aspect s or magnetic properties that will lead to new insights into this behavior, or obtaining examples with specific properties that allow

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13 new chemistry or physics phenomena to be di scovered. For these reasons and more, we have a continuing program to deve lop synthetic methods to new SMMs. In the present work, we have employed N-methyl-diethanolamine (mdaH2) as a route to new Mnx clusters, and some of these have proven to be new SMMs. The choice of mdaH2 was based on our previous successes using pyridine-2,6-dimethanol (pdmH2), which led to many new Mn clusters and severa l new SMMs as a result of its deprotonated forms being versatile N,O,O chelating and br idging ligands. It had previously been found as a chelate in species such as [PtCl2(pdmH2)],23 [TcOCl(pdmH)2],24 and [MoO2(pdm)]n.25 In Mn chemistry, the alkoxide arms also act as bridging groups yielding polynuclear clusters such as [Mn4(O2CMe)2(pdmH)6]2+ with S = 9,26 [Mn9(O2CEt)12(pdm)(pdmH)2(L)2] with S = 11/2,27 and [Mn25O18(OH)2(N3)12(pdm)6(pdmH)6]2+ with S = 51/2.20b All these complexes are SMMs. Deprotonated mdaH2 is similarly a potentially N,O,O chelate, but the absence of a pyridine ring makes it more flexible than pdmH2 and we thus anticipated that it might lead to new types of Mn clusters. We herein report the synthesis and properties of Mn4, Mn6 and Mn12 clusters with mdaH2, and show that the Mn4 and Mn12 complexes are new SMMs. The Mn6 has spin S = 0 but is nevertheless also interesting in being a new structural type in manganese chemistry. We also report DFT calculations on the Mn4 and Mn12 complexes to rationalize their observed ground state S values.

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14 2.2 Experimental Section 2.1.1 Syntheses All chemicals were used as received unless otherwise stated. Mn(O2CPh)2H2O and [Mn3O(O2CMe)6py3](ClO4) were prepared according to the literature methods.28 Abbreviations: mdaH2 = N-methyl-diethanolamine; dpaH = diphenylacetic acid. [Mn12(O2CMe)14(mda)8]MeCN ( 1 ). Method A. mdaH2 (0.23 mL, 2.00 mmol) and NEt3 (0.27 mL, 2.00 mmol) were adde d to a stirred solution of Mn(O2CMe)2 4H2O (0.50 g, 2.00 mmol) in MeCN (30 mL), which cau sed a rapid color change to dark brown. The resulting dark brown solution was stirred for one hour, and then layered with ether. After several days, da rk red crystals of 1 MeCN were collected by filtration, washed with Et2O (2 x 15mL), and dried in air. The yi eld was ~55 %. Elemental analysis for [Mn12(O2CMe)14(mda)8] (C68H130Mn12N8O44); Experimental (calculated): C, 33.71; H, 5.41; N, 4.62. Found: C, 34.02; H, 5.72; N, 4.48 %. Selected FT-IR data (KBr, cm-1): 1581 (s), 1396 (s), 1337 (s), 1080 (s), 1035 (w), 995 (w), 911 (w), 881 (w), 661 (m), 616 (w), 577 (w), 522 (m), 461 (w), 430 (w). Method B. To a stirred solution of MnCl2 4H2O (0.50 g, 2.50 mmol) were added mdaH2 (0.23 mL, 2.00 mmol), NaO2CMe2 (0.41 g, 5.00 mmol) and NEt3 (0.27 mL, 2.00 mmol) in MeCN (30 mL), which caused a rapid color change to dark brown. The resulting dark brown solution was stirre d for one hour and then layered with Et2O. After several days, dark red crystals of 1 MeCN were collected by filtration, washed with ether and dried in air; yield ~46 %. Th e product was identified as complex 1 by IR spectroscopic comparison with material from Method A. Method C. To a stirred solution of complex [Mn3O(O2CMe)6py3](ClO4) (0.50 g, 0.57 mmol) in CH2Cl2 (10 mL) was added mdaH2 (65 L , 0.57 mmol), and the resulting

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15 solution was stirred overnight and filtered. Th e filtrate was layered with toluene and after 3 weeks dark red crystals of 1 MePh were collected by filtrat ion, washed with MePh and dried in air; yield 31-36 %. The product was identified as complex 1 by IR spectroscopic comparison with material from Method A, a nd by elemental analysis. Elemental analysis for [Mn12(O2CMe)14(mda)8] MePh (C75H138Mn12N8O44); Elemental analysis for [Mn12(O2CMe)14(mda)8] (C75H138Mn12N8O44); Experimental (calculated): C, 35.82; H, 5.53; N, 4.46. Found: C, 35.61; H, 5.73; N, 4.45 %. [Mn4(O2CPh)4(mda)2(mdaH)2]CH2Cl2Et2O ( 2 ). mdaH2 (0.17 mL, 1.0 mmol) was added to a stirred solution of Mn(O2CPh)2H2O (0.50 g, 1.0 mmol) and NEt3 (0.21mL, 1.0 mmol) in MeCN (30 mL), whic h caused a rapid color change to dark brown. The solution was stirred for one hour , during which time a brown powder slowly precipitated. This was collected by filtra tion, washed with MeCN, dissolved in CH2Cl2 (50 mL), filtered, and the filtrate layered with Et2O. After several days, light brown crystals of 2 were collected by filtration, washed with ether (2 x 15mL), and dried in air; yield 16%. Elemental analysis for [Mn4(O2CPh)4(mda)2(mdaH)2] (C48H66Mn4N4O16); Experimental (calculated): C, 49.07; H, 5.66; N, 4.77. Found: C, 48.99; H, 5.43; N, 4.56 %. Selected FT-IR data (KBr, cm-1): 1614 (s), 1597 (s), 1574 (s), 1551 (s), 1457 (m), 1338(s), 1340 (s), 1258 (m), 1171 (w), 1132 (w), 1095 (s), 1066 (s), 1050 (s), 994 (w), 913 (m), 883 (w), 869 (w), 809 (w), 712 (s), 674 (s), 654 (m), 593 (m), 534 (m), 509 (m), 458 (w), 436 (m). [Mn6O2(OH)2(dpa)8(mdaH)2]MePh ( 3 ). To a stirred solution of MnCl2 4H2O (0.50 g, 2.50 mmol) in MeCN (40 mL) wa s added dpaH (1.06 g, 5.00 mmol), mdaH2 (0.29 mL, 2.50 mmol) and NEt3 (0.28 mL, 2.00 mmol), which caused a color change to

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16 dark brown. The solution was stirred for 4 h, filtered and layered with toluene. After several days, brown crystals of 3 MePh and a small amount of white precipitate were collected by filtration, washed with cold acetone and dr ied in air; yield 30-35%. Elemental analysis for [Mn6O2(OH)2(dpa)8(mdaH)2] MePh (C129H122Mn6N2O24); Experimental (calculated): C, 64.18; H, 5.09; N, 1.16. Found: C, 64.51; H, 5.43; N, 1.53 %. Selected FT-IR data (KBr, cm-1): 1587 (s), 1559 (s), 1493 (m), 1451 (m), 1398 (s), 1382 (s), 1254 (w), 1238 (w), 1073 (m), 1063 (m), 1031 (m), 998 (w), 743 (s), 717 (s), 696 (s), 642 (s), 571 (w), 557 (w), 465 (w). 2.2.2 X-Ray Crystallography A suitable crystal of 1 MeCN was selected from the bulk sample, maintained in mother liquor to avoid solvent loss, attached to the tip of a glass cap illary and transferred to the goniostat, where it was cooled to 100 K for characterization and data collection. Data were collected on a Bruker AXS P4 diffractometer using MoK radiation ( = 0.71073 ) and were corrected for Lorentz and polarization effects but not for absorption. The structure was solved by direct methods and Fourier techniques (SHELXS-86)29 and refined on |F|2 (SHELXL-97).30 All of the non-hydrogen atoms were refined using anisotropic thermal parameters , while all hydrogen atoms were introduced in fixed, idealized positions with isotropic th ermal parameters equivalent to 1.0 plus the isotropic equivalent of the parent atom. Complex 1 and 3 crystallize in the triclinic space group P 1 while complex 2 crystallizes in monoclinic space group, P 21/ n . For complex 1 , the final R 1 and wR 2 were 4.86 and 8.91 %, respectively.

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17 Data on complexes 2 CH2Cl2Et2O and 3 MePh were collected at 173 K on a Siemens SMART PLATFORM equipped with a CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were refined using up to 8192 reflections. A full sphere of data (1850 frames) was collected using the -scan method (0.3 frame width) . The first 50 frames were re-measured at the end of data collection to monitor instrument and cr ystal stability (maximum correction on I was < 1 %). Absorption corrections by integrati on were applied based on measured indexed crystal faces. Table 2-1. Crystallographic data for complex 1 MeCN, 2 CH2Cl2Et2O and 3 MePh Parameter 1 MeCN 2 CH2Cl2Et2O 3 MePh formulaa C72H136Mn12N10O44 C58H90Cl4Mn4N4O18 C143H138Mn6N2O24 fw, g mol-1 2505.18 1492.90 2598.32 space group P 1 P 21/ n P 1 a , 13.1062(13) 18.069(2) 14.4321(11) b , 13.2707(13) 8.3713(11) 14.8288(12) c , 17.2424(17) 23.707(3) 19.4610(16) , deg 107.223(2) 90 71.192(2) , deg 109.214(2) 102.096(3) 83.369(2) , deg 99.260(2) 90 66.634(2) V , 3 2591.6(4) 3506.3(8) 3618.8(5) Z 1 2 1 T , K 100(2) 173(2) 173(2) mm-1 1.496 0.923 0.571 radiation, b 0.71073 0.71073 0.71073 calc, g cm-3 1.605 1.414 1.193 R 1 ( wR 2) %c , d 4.86 (8.91) 7.18 (18.39) 6.56 (15.46) a Including solvent molecules. b Graphite monochromator. c R 1 = || Fo| – | Fc|| / | Fo|. d wR 2 = [ w ( Fo 2 Fc 2)2] / [ w Fo 2)2]]1/2 where S = [ [ w ( Fo 2 – Fc 2)2] / ( n p )]1/2, w = 1/[ 2( Fo 2) + ( m * p )2 + n * p ], p = [max( Fo 2, 0) + 2* Fc 2]/3, and m and n are constants The structures were solved by Direct Methods in SHELXTL631, and refined on F2 using full-matrix least squares. The non-H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal pos itions and were ridi ng on their respective carbon atoms. The solvent molecules could not be modeled properl y, and thus program

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18 SQUEEZE32, a part of the PLATON33 package of crystallographic software, was used to calculate the solvent disorder area and remove its contribution to the overall intensity data. For complex 2 , a total of 342 parameters were refined in the final cycle of refinement using 18497 reflections with I > 2 (I) to yield R 1 and wR 2 of 7.18 and 18.39 %, respectively. For complex 3 , a total of 702 parameters were refined in the final cycle of refinement using 4877 reflections with I > 2 (I) to yield R 1 and wR 2 of 6.56 and 15.46 %, respectively. Crystallograp hic unit cell and structure so lution data are listed in Table 2-1. 2.2.3 Computational Studies Computational Studies were performe d by Dr. Ted A. O’Brien at Indiana University-Purdue University Indianapolis. Complex 1 was treated with ZILSH but not DFT, owing to its large size. Refined energies were obtained using DFT for seve ral model clusters, and substituted into equations with spin couplings found with ZILSH. For complex 2 , calculations were carried out for the complex and a model complex with a reduced number of atoms using ZILSH. All ZILSH calculations followed the proce dure described in reference 34. The DFT calculations were performed using the B3LYP functional35 implemented in either the Gaussian 98 program36 or the Gaussian 03 program.37 Several basis sets were used for complex 1 , including a), the all-elec tron Dunning-Huzinaga doublebasis for light atoms38 and the Los Alamos effectiv e core potentia l plus doublevalence basis set for manganese atoms (LANL2DZ);39 and b) the 6-31G(d) basis set.40-44 The model of

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19 complex 1 (described below) was additionally treated with c), the TZVP basis set of Alrichs and coworkers.45 2.3 Results and Discussion 2.3.1 Syntheses The described compounds resulted from an investigation of th e reactions of mdaH2 with various Mn sources and under a vari ety of conditions. The reaction between Mn(O2CMe)2H2O and 1 equivalent each of mdaH2 and NEt3 in MeCN resulted in the formation of a brown solution from which was obtained of 1 MeCN as dark red crystals in 55 % yield. Complex 1 was also obtained from the reaction of MnCl2, NaO2CMe and mdaH2 in a 1:2:1 ratio in the presence of NEt3. The average Mn oxidation state in [Mn12(O2CMe)14(mda)8] ( 1 ) is +2.5 (MnIII 6MnII 6), which is higher than the MnII starting material and indicates the i nvolvement of atmospheric O2 in the reaction since no other oxidizing agent is available in the reaction. The formation of 1 is summarized in Eq. 2-1. 12 Mn(O2Me)2 + 8 mdaH2 + 6 NEt3 [Mn12(O2CMe)14(mda)8] + 6 NHEt3+ + 10 MeCO2H + 6 e(2-1) Since oxidation of only some of the MnII occurs during the reaction, it was also investigated whethe r starting with a MnIII reagent might lead to a different product. However, the reaction using [Mn3O(O2CMe)6py3](ClO4) (MnIII 3), as the Mn source again gave complex 1 as the isolated product. In order to explore the infl uence of the carboxylate on the nature of the product, the same reaction was performed with th e more bulky benzoate groups using Mn(O2CPh)2H2O as the Mn source. Indeed, the is olated product was now found not to be the benzoate analog of 1 but instead the complex [Mn4(O2CPh)4(mda)2(mdaH)2] ( 2 ), obtained as the 2 CH2Cl2Et2O solvate. The yield is lo w (16%), however, and it is

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20 possible that the benzoate analog of 1 is more soluble than 1 and thus remains in the filtrate solution, although we did not isolate other products from this reaction. Complex 2 is again mixed-valence (MnII 2MnIII 2), indicating the atmospheric oxidation of some of the MnII. The same product was obtained using MnCl2 with Na(O2CPh)2 and mdaH2 in a 1:2:1 ratio, in the presence of NEt3, but in a lower isolated yield (6 %). 4 Mn(O2CPh)2 + 4 mdaH2 + 2 NEt3 [Mn4(O2CPh)4(mda)2(mdaH)2] + 2 NHEt3 + + 4 PhCO2H + 2 e(2-2) Extending this reaction, we employed an ev en bulkier carboxylate to explore if the identity of the isolated product would again be affected. The acid chosen was diphenylacetic acid (dpaH), a nd the reaction was between MnCl2 4H2O, dpaH, and NEt3 in a 1:2:1 ratio, and the isolated product was again mixed-valence; the complex [Mn6O2(OH)2(dpa)8(mdaH)2] ( 3 ) was obtained as brown crystals of 3 MePh in ~35% yield. The crystals were contaminated with trace amounts of a white powder, requiring some manual separation. The formation of 3 is summarized in Eq. 2-3, again involving oxidation of MnII by (presumably) atmospheric oxygen. 6 MnCl2+ 8 dpaH + 2 mdaH2 + 4 NEt3 + 4 H2O [Mn6O2(OH)2(dpa)8(mdaH)2] + 4 Et3NH+ + 12 HCl + 4 e(2-3) Apart from the obvious difference in the nuclearity of complex 3 compared with 1 and 2 , there is another big difference in that 3 contains oxide and hydroxide bridges, whereas neither 1 nor 2 does, all the bridges in the latter complexes being from mda2or mdaHgroups (vide infra).

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21 2.3.2 Description of the Structures 2.3.2.1 Structure of [Mn12(O2CMe)14(mda)8] (1) Two different views of the structure of centrosymmetric [Mn12(O2CMe)14(mda)8] ( 1 ) are shown in Figure 2-1, and selected metr ic parameters are listed in Table A-1. Complex 1 is a new structural type in Mn chemistry and consists of a Mn12 loop (Figure 2-1) that is mixed-valent (MnII 6MnIII 6) and possesses a chair c onformation (Figure 2-2). All Mn centers are six-coor dinate with near-octahedral geometries, except MnII ions Mn4 and Mn4', which are seven-coordinate a nd possess a very distorted pentagonal bipyramidal geometry. Six of the mda2ligands bind as tridentate chelates to each MnIII ion, and their two alkoxide O atom s bridging to the adjacent MnII ions. The remaining two mda2groups chelate MnII ions (Mn4, Mn4') and bridge by their alkoxide O atoms to adjacent MnIII ions. As a result, the mda2groups alternate between being axial and equatorial with respect to the Mn12 loop. In addition, note that all mda2alkoxide groups bridge a MnIIMnIII pair, and this bridging mode is consistent with the mda2being doublydeprotonated. Each pair is additionally bridged by an acetate group in its familiar 1, 1, ( syn , syn ) binding mode on the outside of the loop, whereas the fina l two acetate groups bridge Mn2/Mn1/Mn6' and the symmetry related trio in a rarer 1, 2, 3 mode on the inside of the loop. The MnII or MnIII oxidation state assignments were established by consideration of bond distances, bond-valence sum (B VS) calculations (Table 2-2).46, 47 A bond valence sum (BVS) is an empirical value based on cr ystallographically determined metal-ligand distances that is routin ely used to determine the oxidation level of an atom in a molecule.

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22 Mn1 Mn2 Mn3 Mn4 Mn5 Mn6 N1 N2 N3 Mn1' Mn2' Mn3' Mn4' Mn5' Mn6' O3 O4 O7 O8 O10 O11 O14 O15 O17 O18 N4 O22 Mn1 Mn2 Mn3 Mn4 Mn5 Mn6 N1 N2 N3 Mn1' Mn2' Mn3' Mn4' Mn5' Mn6' O3 O4 O7 O8 O10 O11 O14 O15 O17 O18 N4 O22 Figure 2-1. ORTEP representation in PovRay format of [Mn12(O2CMe)14(mda)8] ( 1 ), where the relative disposition of the Ja hn-Teller elongation ax es are indicated as solid black bonds. MnIII green; MnII orange; O red; N lightblue; C gray. H have been omitted for clarity Figure 2-2. ORTEP representation in PovRay format of [Mn12(O2CMe)14(mda)8] ( 1 ) showing the chair conformation in a side view and the relative disposition of the Jahn-Teller elongation axes indicated as solid black bonds. MnIII green; MnII orange; O red; N lightblue; C gray

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23 The valence of the ith atom, Vi, can be defined in terms of the sum of the individual bond valences, sij, of the atom i with those atoms, j , in its coordination sphere (Eq. 2-4).48 jj b R R ij iije s V] / ) [(0 (2-4) The valences of the individual bonds, sij, can be calculated from the observed bond length in the crystal structure of a molecule using Eq. 2-4, where Rij is the observed bond length, R0 is the length expected for a bond of unit valence and b is an experimentally determined constant equal to 0.37. Values of R0 for Mn-O bonds for Mnn+ (n = 2, 3, 4, and 7) are available,49 allowing the application of this calcu lation to determine the oxidation states of the Mn centers in our clusters. The cal culations can also be extended to include inorganic oxygen atoms and are a useful m eans of assessing the protonation levels of such atoms in a complex. In addition to transition metal clusters, bond valence sum analysis has been used to determine th e oxidation states of metal centers in metalloenzymes47a, 50 and superconductors.51 Table 2-2. Bond valence sum calculationsa for complex 1 2 CH3CN Atom Mn2+ Mn3+ Mn4+ Mn(1) 3.076 2.828 2.942 Mn(2) 2.076 1.898 1.993 Mn(3) 3.183 2.951 3.072 Mn(4) 2.087 1.744 1.812 Mn(5) 3.261 2.963 2.812 Mn(6) 2.005 1.834 1.925 a The underlined value is the one closest to the actual charge for which it was calculated. The oxidation state of a particular atom can be taken as the nearest whole number to the underlined value Additionally, the presence of Jahn-Teller (JT) axial elong ations at six of the Mn ions, as expected for high-spin MnIII in near-octahedral geometry, help to establish the oxidation state assignments of the Mn ; the JT axes all contain the mda2N atoms (N1, N2, N3) (solid black bonds in Figure 2-2). Th e parallel alignment is the origin of the

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24 significant magnetic anisotropy in the z direction that greatly influences the observed magnetic properties (vide infra).The obtained MnII 6MnIII 6 description is consistent with complete deprotonation of the mda2groups and the neutral nature of the molecule. A BVS calculation was also carried out for the inorganic O atoms, confirming the deprotonation of the mda2group where the O atoms are all deprotonated (Table 2-3). Table 2-3. Bond valence sum calculationsa for selected oxygen atoms in complex 1 Atom Vi Assignment O(3) 1.837 O2O(4) 1.951 O2O(7) 1.929 O2O(8) 1.853 O2O(10) 1.900 O2O(11) 1.768 O2O(14) 1.849 O2O(15) 1.889 O2O(17) 1.918 O2O(18) 1.827 O2O(22) 1.851 O2a The oxygen atom is O2if Vi 2, OHif Vi 1, and H2O if Vi 0 2.3.2.2 Structure of [Mn4(O2CPh)4(mda)2(mdaH)2] (2) The structure and metric parameters for centrosymmetric [Mn4(O2CPh)4(mda)2(mdaH)2] ( 2 ) are presented in Figure 2-3 and Table A-2, respectively. Complex 2 consists of a planar Mn4 rhombus that can be described as two edge-fused, oxo-capped Mn3 triangular units. Inspection of structural parameters, BVS calculations (Table 2-4), and identification of MnIII JT elongation axes at Mn1/Mn1' identified the latter as MnIII and Mn2/Mn2' as MnII atoms. Charge neutralization thus requires that two of the chelate groups are mono-protonated (i.e., mdaH-), and the protonated O atoms were iden tified as O8 and O8' by their BVS being only 1.15, as expected for a protonated O whose bound H+ is not located for inclusion in the BVS calculation.

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25 N1 Mn1 N2' N1' Mn2' Mn2 O8 N2 O3 O4 O7 O5 O8' O7' O3' O4' Mn1' O5' N1 Mn1 N2' N1' Mn2' Mn2 O8 N2 O3 O4 O7 O5 O8' O7' O3' O4' Mn1' O5' Figure 2-3. ORTEP representation in PovRay format of [Mn4(O2CPh2)4(mda)2(mdaH)2] ( 2 ) and the relative dispos ition of the Jahn-Teller el ongation axes indicated as solid black bonds. MnII orange; MnIII green; O red; N lightblue; C gray. H atoms have been omitted for clarity Table 2-4. Bond valence sum calculationsa for complex 2 Atom Mn2+ Mn3+ Mn4+ Mn(1) 3.278 3.014 3.139 Mn(2) 1.865 1.718 1.783 a The underlined value is the one closest to the actual charge for which it was calculated. The oxidation state of a particular atom can be taken as the nearest whole number to the underlined value Table 2-5. Bond valence sum calculationsa for selected oxygen atoms in complex 2 Atom Vi Assignment O(3) 1.949 O2O(4) 1.852 O2O(5) 1.856 O2O(8) 1.153 OHa The oxygen atoms is O2if Vi 2, OHif Vi 1, and H2O if Vi 0

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26 This conclusion was confirmed by the pr esence of OHO hydrogen-bonds between protonated O8 and the adjacent benzoate O, atom O7 (O8O7 = 2.603 ). Each MnIII ion is chelated by a tridentate mda2group, one of whose al koxide O atoms (O3) doubly bridges to Mn2, and the othe r (O4) triply bridges to Mn1' and Mn2'. The two mdaHgroups also each bind in a tridentate fashi on, with the deprotonated alkoxide O atoms (O5) doubly bridging to Mn2' and protonated O8 terminally bound to Mn2. Two additional benzoate groups, each bridging a MnII/MnIII pair, complete the ligation, making Mn1 and Mn2 sixand se ven-coordinate, respectively. The JT distortion axes at Mn1 and Mn1' are along the O4-Mn1-N1 and O4'-Mn1'-N1' axes, and are shown as the solid black bonds in Figure 2-3. The structure of complex 2 is with precedent in Mn chemistry, being similar for example with that of the complex [Mn4(O2CMe)2(pdmH)6]2+.26 2.3.2.3 Structure of [Mn6O2(OH)2(dpa)8(mdaH)2] (3) The structure and metric parameters for centrosymmetric [Mn6O2(OH)2(dpa)8(mdaH)2] ( 3 ) are presented in Figure 24, Figure 2-5 and Table A-3, respectively. The complex is again a new stru ctural type in Mn ch emistry, and also the first example where a complex with the mda2or mdaHligand also contains oxide and hydroxide bridges. The core can be de scribed as consisting of a planar MnIII 4 rhombus with each outer edge bridged by an O atom to give a cyclohexane-like unit with a chair conformation. To each pair of these O atoms is attached a MnII atom above and below the plane of the MnIII 4 rhombus, with each MnII also bridged to the central MnIII atoms (Mn2, Mn2') by 3-O2ions O5 and O5'. Alternatively, the structure can be described as a MnIII 2MnII 2 planar rhombus (Mn1, Mn2, and their symmetry partners) with M n3 and Mn3' bound on either side of this

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27 rhombus. An additional and convenient description of the Mn6 topology is as two Mn4 distorted tetrahedra fused along th e Mn2/Mn2' edge (Figure 2-5b). Mn2 Mn1 Mn3 O11 O2 O5 N1 O10 Mn1' Mn2' Mn3' Mn2 Mn1 Mn3 O11 O2 O5 N1 O10 Mn1' Mn2' Mn3' Figure 2-4. ORTEP representation in PovRay format of [Mn6O2(OH)2(dpa)8(mdaH)2] ( 3 ), top view, the relative dis position of the Jahn-Teller elongation axes indicated as solid black bonds. MnII orange; MnIII green; O red; N lightblue; C gray. The phenyl rings of dpaH (except for th e ipso carbon atom) and the hydrogen atoms have been omitted for clarity Mn3 Mn1 Mn2 N1 O2 O10 O5 O11 Mn1' Mn2' Mn3' Mn3 Mn1 Mn2 N1 O2 O10 O5 O11 Mn1' Mn2' Mn3' a) b) Mn3 Mn1 Mn2 N1 O2 O10 O5 O11 Mn1' Mn2' Mn3' Mn3 Mn1 Mn2 N1 O2 O10 O5 O11 Mn1' Mn2' Mn3' a) b) Figure 2-5. ORTEP representation in PovRay format of [Mn6O2(OH)2(dpa)8(mdaH)2] ( 3 ), side view, and the relative dispositio n of the Jahn-Teller elongation axes indicated as solid black bonds (a) and a view of the distorte d tetrahedra (b). MnII orange; MnIII green; O red; N lightblue; C gray. The phenyl rings of dpaH (except for the ipso carbon atom) and the hydrogen atoms have been omitted for clarity

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28 The complex is again mixed-valence, MnIII 4MnII 2, but unlike both 1 and 2 it does not contain equal amounts of MnII and MnIII. This conclusion was reached by inspection of structural parameters, BVS calculations (Table 2-6), and identification of MnIII JT elongation axes at Mn2, Mn3 a nd their symmetry partners. Table 2-6. Bond valence sum calculationsa for complex 3 Atom Mn2+ Mn3+ Mn4+ Mn(1) 1.961 1.793 1.883 Mn(2) 3.156 2.887 3.030 Mn(3) 3.165 2.921 3.024 a The underlined value is the one closest to the actual charge for which it was calculated. The oxidation state of a particular atom can be taken as the nearest whole number to the underlined value Consideration of charge ba lance requires some O atoms to be protonated, and O BVS calculations (Table 2-7) identified O2 and O2' as OHions, and O10 and O10' to be alcohol groups (i.e., of mdaHgroups). The protonated O10 from the alcohol group (mdaH-) forms a hydrogen bond with the O5 (O10O5 = 2.579 ). Each mdaHgroup chelates a MnIII atom, with its alcohol arm termina lly coordinated a nd its alkoxide arm bridging to an adjacent MnIII. Table 2-7. Bond valence sum calculationsa for selected oxygen atoms in complex 3 Atom Vi Assignment O(1) 1.823 O2O(2) 1.077 OHO(3) 1.917 O2O(4) 1.906 O2O(5) 1.684 O2O(6) 1.780 O2O(7) 1.925 O2O(8) 1.809 O2O(9) 1.833 O2O(10) 1.141 OHO(11) 1.745 O2O(12) 1.945 O2a The oxygen atoms is O2if Vi 2, OHif Vi 1, and H2O if Vi 0

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29 All the Mn atoms are six-coordinate, w ith the peripheral ligation completed by 1, 1, ( syn , syn ) dpagroups and a monodentate dpagroup on Mn3 and Mn3', with the unbound O atom forming a hydrogen-bond to th e hydroxide group (O11O2 = 2.660 ). 2.3.3 Magnetochemistry of Complexes 1, 2 and 3 2.3.3.1 Direct current magnetic studies of complexes 1 and 2 Variable-temperature magnetic susceptib ility measurements were performed on powdered polycrystalline samples of complexes 1 3 , restrained in eicosane to prevent torquing, in a 0.1 T field and in the 5 .0 -300 K range. The data are shown as MT vs. T plots in Figure 2-6 and 2-7. MT for complex 1 steadily decreases with decr easing temperature from 41.5 cm3mol-1K at 300 K to 23.3 cm3mol-1K at 5.0 K. The 300 K value is slightly below the spin-only value of 44.25 cm3 mol-1 K expected for a complex consisting of six Mn(II) and six Mn(III) non-interacting ions, indi cating the presence of predominantly antiferromagnetic exchange inte ractions within the molecule. However, the 5.0 K value is still far from zero, suggesting that 1 possesses a fairly large ground state spin value of S = 6 or 7. For complex 2 , MT steadily increases from 17.58 cm3mol-1K at 300 K to a maximum of 32.88 cm3mol-1K at 8.0 K, followed by a decrease to 31.60 cm3mol-1K at 5.0 K. The 300 K value is higher than the 14.75 cm3mol-1K spin-only value expected for two MnII and two MnIII non-interacting ions. This and the increase in MT with decreasing temperature indicate predominantly ferromagnetic interactions within the molecule, and the 5.0 K value is consistent with an S = 8 or 9 ground state. The low temperature decrease is likely due to a comb ination of zero-field splitting (ZFS), Zeeman effects from the applied dc field, and any w eak antiferromagnetic exchange interactions.

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30 Temperature (K) 050100150200250300 M T (cm 3 mol -1 K) 15 20 25 30 35 40 45 Complex 1 Complex 2 Figure 2-6. Plot of MT vs. temperature for a dried, micr ocrystalline sample of complexes 1 and 2 in eicosane, measured in a 1.0 kG field The MT in the 5.00-300 K range on a powdered microcrystalline sample of 3 MePh decreases steadily with d ecreasing temperature from 17.63 cm3mol-1 K at 300 K to 12.11 cm3mol-1K at 70 K, and then to 1.39 cm3mol-1K at 5.0 K, and is clearly heading for 0 cm3mol-1K at 0 K, indicating the presence of predominantly antiferromagnetic exchange interactions with in the molecule and an S = 0 ground state. This was confirmed by ac magnetic suceptibility measurements carried out on a dried, microcrystalline sample of 3 MePh in a 3.5 G AC field oscillating at 1000 Hz. In the inset of Figure 2-7 is shown the in-phase ac susceptibility, plotted as M' T versus T , which confirms the expected S = 0 state with g = 2. The value at 300 K is less than 20.75 cm3 K mol-1, the spin-only value expected for a 2MnII, 4MnIII complex with noninteracting metal centers, indicating the presence of appreciable an tiferromagnetic interactions between the manganese ions and suggesting a small ground state spin.

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31 Temperature (K) 050100150200250300 M T (cm 3 mol -1 K) 0 5 10 15 20 024681012 M'T (cm3 mol-1 K) 0 2 4 Figure 2-7. Plot of MT vs. temperature for a dried, microcrystalline sample of complex 3 MePh in eicosane, measured in a 1.0 kG field. The inset plot is the in-phase ac susceptibility, plotted as M T versus T To determine the values of the ma ny pairwise exchange parameters ( Jij) between two Mn atoms Mni and Mnj in complexes 1 3 , and to find all of th e possible spin states and their energies, the appropr iate spin Hamiltonians for these complexes would have to be diagonalized. However, such a matrix diagonalization appr oach would involve matrices of dimensions of 7.29 x 108 by 7.29 x 108, 900 by 900 and 2.25 x 104 by 2.25 x 104 for 1 3 , respectively. Such calculations are essentially impossible for 1 and 3 , and very difficult for 2 . It is also not possible, due to the complexity and/or low symmetry of complexes 1 and 3 , to apply the equivalent operator approach, based on the Kambe vector coupling method,52 as is usually possible with sma ller systems. This approach is, however, possible for Mn4 complex 2 , and has been carried out. In addition, we will describe later a computational investigation by DFT methods of the exchange parameters and resulting ground state S values for complexes 1 and 2 ( vide infra ). For complex 2 , the crystallographic Ci symmetry of the complex in the solid state requires four exchange parameters to descri be all the pairwise ex change interactions. However, the core of the molecule approximates to virtual C2v symmetry, requiring only

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32 three exchange intera ctions, one between the central pair of MnIII atoms, Mn1/Mn1', a second between the two MnII atoms Mn2/Mn2', and a third for the four MnII/MnIII interactions corresponding to the four edges of the Mn4 rhombus; the latter fall into two groups by symmetry but these are ve ry similar, both involving MnIIMnIII pairs bridged by a mdaHalkoxide O atom. We have employed this virtual symmetry to obtain the exchange parameters in this complex using the Kambe method, and this will also allow a comparison later with the parameters obtai ned from the computational calculations described below. The isotropic Heisenberg-Dirac-Van Vleck (HDVV)57 spin Hamiltonian describing the exchange inter actions within the virtual C2v symmetry core of 2 is given by Eq. 2-5. H = – 2 Jbb( 1 1 ) – 2 Jwb ( 1 2 + 1 2 + 1 2 + 1 2) – 2 Jww( 2 2 ) (2-5) where iS refers to the spin of Mn atom Mni, and Jwb, Jww, and Jbb are the exchange parameters between MnII/MnIII , MnII/MnII and MnIII/MnIII ions, respectively. The labels w (= wingtip) and b (= body) refer to the body and wingtip positions of a butterfly, the description we have often found convenient for referring to the various positions of such a Mn4 rhombus. The spin Hamiltonian in Eq. 2-5 was transformed into an equivalent form, given in Eq. 2-6, by applying the Kamb vector coupling method52 and the substitutions A = 1 + 1 , B = 2 + 2 , and T = A + B, where T is the resultant spin of the complete molecule. H = – Jwb ( T 2 – A 2 – B 2) – Jbb ( A 2 – 1 2 – 1 2) – Jww ( B 2 – 2 2 – 2 2) (2-6)

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33 The energies E ST > of the resultant spin states, ST, are the eigenvalues of Eq. 2-6, and these are given by Eq. 2-7, where all consta nt terms contributing e qually to all states have been omitted. E ST, SA, SB > = – Jwb[ ST( ST+1) – SA( SA+1) – SB( SB+1)] – Jbb[ SA( SA+1)] –Jww[ SB( SB+1)] (2-7) A theoretical MT vs . T expression was derived using the possible ST values, their energies E ( ST), and the Van Vleck equation (see A ppendix D-1), and th is expression was used to fit the experimental data. Temperature (K) 050100150200250300 M T (cm 3 mol -1 K) 15 20 25 30 35 exp fitting Figure 2-8. Plot of MT vs. temperature for a dried, microcrystalline sample of complex 2 in eicosane. M is the dc molar magnetic sus ceptibility measured in a 1.0 kG field. The solid line is the fit of the data to the theoretical equation; see the text for the fit parameters Data below 8 K were omitted because the low-temperature decrease is caused by factors not included in the above model (Figure 2-8). The fit parameters were Jbb, Jwb, Jww and g , and gave Jbb = 41 cm-1, Jwb = 1.6 cm-1, Jww = -0.7 cm-1, g = 1.79 and 0.2 % paramagnetic impurity term; temperature-independent paramagnetism (TIP) was included as a constant of 400 10-6 cm3 mol-1. The obtained J parameters from the fit indicate the complex to possess an S = 9 ground state, the 9, 4, 5 > state.

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34 To confirm the ground state spin S and to determine the ma gnitude of the zero-field splitting parameter D, magnetization vs. dc fi eld measurements were made on samples of 1 and 2 restrained in eicosane at applied magnetic fields and temperatures in the 1-30 kG (0.1-3 T) and 1.8-2.5 K ranges, respectively. The data were fit to a model that assumes only the ground state is populated, in cludes axial zero-field splitting ( D z 2) and the Zeeman interaction ( g B H ), and incorporates a full powder-average.53 This was performed using the program MAGNET,54 which fit the experimental data to those calculated using the above proced ure for different values of S , D and g . H/T (kG/K) 024681012141618 M/N B 0 2 4 6 8 10 12 14 0.1 T 0.5 T 1 T 2 T 3 T fitting H/T (kG/K) 024681012141618 M/N B 0 2 4 6 8 10 12 14 16 0.1T 0.5 T 1 T 2 T 3 T fitting a) b) H/T (kG/K) 024681012141618 M/N B 0 2 4 6 8 10 12 14 0.1 T 0.5 T 1 T 2 T 3 T fitting H/T (kG/K) 024681012141618 M/N B 0 2 4 6 8 10 12 14 16 0.1T 0.5 T 1 T 2 T 3 T fitting H/T (kG/K) 024681012141618 M/N B 0 2 4 6 8 10 12 14 0.1 T 0.5 T 1 T 2 T 3 T fitting H/T (kG/K) 024681012141618 M/N B 0 2 4 6 8 10 12 14 16 0.1T 0.5 T 1 T 2 T 3 T fitting a) b) Figure 2-9. Determination of ground state spin. Plot of reduced magnetization M / N B vs. H / T for a dried, microcrystalline sample of complexes 1 (a) and 2 (b) in eicosane; the dc field value of each of the isofield plots is indicated The experimental data are plotted in Figure 2-9 as reduced magnetization ( M / N B) vs. H / T , where M (=MH ) is the molar magnetization, N is Avogadro’s number, B is the Bohr magneton, and H is the magnetic field. The fit of the data for complex 1 is shown as the solid lines in Figure 2-9a, and the fit parameters were S = 7, g = 1.92 and D = -0.26 cm-1. The fit of the data for complex 2 is shown as the solid lines in Figure 2-9b, and the fit parameters were S = 9, g = 1.78, and D = -0.12 cm-1. To ensure that the global fitting minimu m had been obtained and to assess the precision in the obtained D and g parameters, root-mean-square fitting error surfaces

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35 were generated as a function of g and D, and those for complexes 1 and 2 are shown in Figure 2-10 as 2-D contour plots. These plot s display only the region of error space with negative D values; as is usually the case, accep table fits could also be found in both cases with positive D values, but the fits with negative D were cl early superior in the present cases. In addition, the results to be described later confirm that D is negative. As can be seen in Figure 2-10, there is only one error minimum in each of the fits, and these are relatively hard (i.e., well define d). This allows us to conclu de that the estimated precision of the obtained D and g values is 0.01 cm-1 and 0.03, respectively. g 1.61.71.81.92.0 D (cm-1) -0.3 -0.2 -0.1 0.0 g 1.71.81.92.02.12.2 D (cm-1) -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 a) b) g 1.61.71.81.92.0 D (cm-1) -0.3 -0.2 -0.1 0.0 g 1.71.81.92.02.12.2 D (cm-1) -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 g 1.61.71.81.92.0 D (cm-1) -0.3 -0.2 -0.1 0.0 g 1.71.81.92.02.12.2 D (cm-1) -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 a) b) Figure 2-10. Determination of ground state sp in. Two-dimensional contour plot of the error surface for the D vs. g fit for complexes 1 (a) and 2 (b). The asterisk indicates the soft minimum However, the accuracy of these values is more difficult to assess, because magnetization fits are a good but not the best way to obtain accurate D and g values. Techniques such as EPR are much better for this purpose. The large ground state spin values of 1 and 2 and their associated significant magnetoanisotropy (D values) suggested that these complexes might be new examples of single-molecule magnets (SMMs). As stated ear lier, this requires a significant barrier ( U )

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36 to magnetization relaxation (reorientation), and the upper limit to this is given by S2 D for an integer spin system, or 12.74 cm-1 (18.33 K) and 9.72 cm-1 (13.98 K) for 1 and 2 , respectively, using the magnetization fit paramete rs. In fact, the true or effective barrier ( Ueff) is usually significantly smaller than U due to QTM. We thus decided to investigate the magnetization dynamics of these complexes using ac magnetic susceptibility studies. 2.3.3.2 Alternating current magnet ic susceptibility studies Ac studies were performed in the 1.8-10 K range using a 3.5 G ac field oscillating at frequencies in the 25 – 1488 Hz range. The results for complexes 1 and 2 are shown in Figure 2-11. If the magnetization vector can relax fast enough to keep up with the oscillating field, then there is no imagin ary (out-of-phase) susceptibility signal (M ), and the real (in-phase) susceptibility (M ) is equal to the dc susceptibility. However, if the barrier to magnetization relaxation is si gnificant compared to thermal energy ( kT ), then there is a non-zero M signal and the in-phase signa l decreases. In addition, the M signal will be frequency-depende nt. Such frequency-dependent M signals are a characteristic signature of the superpar amagnetic-like propertie s of a SMM, but by themselves do not prove the presence of a SMM. For complex 1 , the ac data in Figure 2-11a reveal several things: (i) the in-phase M T in Figure 2-11a (top) increases with decreasing temperature indicating the depopulation of excited states with spin S less than that of the gr ound state; (ii) at ~4 K, M T at 50 Hz has almost reached a plateau, risi ng only slightly below this temperature; (iii) extrapolation of the M T value to 0 K gives 27.5 cm3mol-1K, indicating an S = 7 ground state for the molecule. M T is given by g2S ( S +1)/8, so 27.5 cm3mol-1K gives S = 7 and g = 1.98, in excellent agreement with the re sult of the dc magnetization fit; (iv)

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37 there is a frequency-dependent decrease in M T at the lowest temperatures, with the decrease becoming apparent at higher temperatures as the ac frequency increases; and (v) concomitant with (iv) there is a frequency-de pendent increase in the out-of-phase signal M , with only the tails visible above 1.8 K (the operating limit of our SQUID magnetometer) of peaks that clea rly lie at lower temperatures. With regards to point (iii), we have disc ussed in several prev ious publications the importance of using ac data to help determin e accurately the ground state spin value. A common way of determining ground state S is to use dc magnetiza tion fits such as those in Figure 2-9, but great care must be taken because these assume only the ground state is populated. As a consequence, erroneous conclusions about S may result when either (a) there are very low-lying excited states essentially degenerate with the ground state so that they are populated even at the lowest temp eratures employed, or (b ) there are low-lying excited states that perhaps are not essentia lly degenerate with the ground state but which have S values greater than that of the gr ound state. Both situations (a) and (b) are common problems when the molecule is of high nuclearity and there is thus a high density of states and/or the molecule contains MnII ions, since these result in (usually) very weak antiferromagnetic exchange interac tions and thus small energy gaps between spin states. The applied dc field will ra ise the degeneracy of the MS levels of the ground and low-lying spin states, and at large fields bot h situations (a) and (b ) can cause the wrong ground state spin assignment because the largest MS levels of excited states will approach and even cross with those of the ground state, leading to an apparently larger ground state S than the true one. The ac experiment rem oves this problem by dispensing with a dc

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38 field completely: low-lying excited stat es then simply show up as a sloping M T vs. T plot, and extrapolation to 0 K, at which only the ground state will be populated, then yields the correct ground state S value. The only problem might occasionally be the presence of weak, usually antiferromagnetic, intermolecular exchange interactions, but even this problem can be circumvented by avoiding beginning the extrapolation at too low a temperature. Temperature (K) 0246810 M'' (cm 3 mol -1 ) 0 1 2 3 4 5 6 M'T (cm 3 Kmol -1 ) 15 20 25 30 35 40 45 1488 Hz 250 Hz 25 Hz M'T (cm 3 K mol -1 ) 22 24 26 28 30 1488 Hz 250 Hz 50 Hz Temperature (K) 0246810 M" (cm 3 mol -1 ) -1 0 1 2 3 4 5 a) b) Temperature (K) 0246810 M'' (cm 3 mol -1 ) 0 1 2 3 4 5 6 M'T (cm 3 Kmol -1 ) 15 20 25 30 35 40 45 1488 Hz 250 Hz 25 Hz M'T (cm 3 K mol -1 ) 22 24 26 28 30 1488 Hz 250 Hz 50 Hz Temperature (K) 0246810 M" (cm 3 mol -1 ) -1 0 1 2 3 4 5 a) b) Figure 2-11. Plot of the in-phase (as M T ) and out-of-phase ( M ) AC susceptibility signals vs. temperature for dried, microcrystalline samples of (a) complex 1 and (b) complex 2 in eicosane at the indica ted oscillation frequencies Thus, the data for 1 in Figure 2-11 a (top) repres ent a textbook example of the utility of the ac in-phase M T vs . T plot for determining the ground state S value of a high nuclearity molecule with a rich content of MnII ions. Note that in anticipation of problems from low-lying excited states when we carri ed out the magnetization fit of Figure 2-9, we used only dc fields up to 3 T; when we includ ed the data collected with higher dc fields,

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39 the quality of the fits lessened, and a higher ground state S value was indicated, which is consistent with crossover of MS levels from excited states with S > 7. For complex 2 , the ac data in Figure 2-11 b are qu alitatively very similar to those for 1 . M T increases with decreasing temperature as low-lying excited states with S less than that of the ground state are populated. Unlike 1 , the ground state S = 9 for 2 is the maximum possible for a MnIII 2MnII 2 system, and thus all excited states must of course have a spin of S < 9. Extrapolation of M T to 0 K gives ~39 cm3mol-1K, which is consistent with S = 9 and g ~ 1.86, again in satisfying ag reement with the re sults of the dc magnetization fit of Figure 2-9. At the lowe st temperatures, there is a frequencydependent decrease in M T , concomitant with the appearan ce of a frequency-dependent out-of-phase M signal below 3 K. The peak of this signal is evident at the highest frequency of 1488 Hz. The appearance of M signals in Figure 2-11 (bottom) suggests, but does not prove, that these two complexes are single-mo lecule magnets SMMs. To confirm if they are indeed SMMs, studies of magnetization vs. dc field sweeps were necessary at temperatures < 1.8 K to see if magnetizati on hysteresis loops would be obtained, the diagnostic property of a magnet. These were ca rried out on single crysta ls at temperatures down to 0.04 K using a micro-SQUID apparatus.55 2.3.3.3 Magnetization vs. dc field hysteresis loops Shown in Figures 2-12 and 2-13 ar e the results of magnetization ( M ) vs. applied dc field scans for single crystals of 1 MeCN and 2 CH2Cl2Et2O, respectively. In each figure are shown (i) the temperature dependence at a fixed sweep rate, and (ii) the field sweep rate dependence at a fixed temperature. For 1 MeCN in Figure 2-12a, hysteresis

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40 loops are clearly evident below approximat ely 1.0 K whose coercivity increases with decreasing temperature down to 0.3 K, as expected for the superparamagnet-like properties of a SMM. At 0.3 K and below, th e hysteresis loops are no longer temperature dependent, suggesting the temperature-independe nt relaxation charac teristic of quantum tunneling of the magnetization (Q TM) via only the ground state MS = 7 levels of the S = 7 spin manifold. Also evident in Figure 212a are steps in the hys teresis loops at zero field and ~ 0.42 T corresponding to field posit ions at which QTM through the anisotropy barrier can occur, starting from the lowest energy MS = -7 level. At temperatures above 0.4 K, additional steps appear at intermedia te field positions, and these are assigned to QTM starting from higher energy MS levels that become populat ed as the temperature is raised. The field sweep dependence at a cons tant temperature of 0.04 K in Figure 2-12b shows that the size of the step at zero fi eld increases with decreasing sweep rate, as expected for a SMM from standard Landau-Ze ner theory, since the tunneling probability is inversely proportional to the sweep rate.56 Complex 1 is a very rare example of a SMM with a single-strand loop structure, with only a Ni12 complex with S = 12 having been previously reported.17d The observation of clearly resolved QTM st eps allowed an estimate of the D value to be obtained from the step separation ( H), thus providing an al ternative experimental route to D. The relevant rela tionship is given in Eq. 2-8, D / g = B H (2-8) where B = 4.6686 x 10-5 cm-1G-1 in the appropriate units, and H is measured in G (10-4 T). Using the step separation of ~0.42 T (4200G), this gives D / g 0.20 cm-1 (0.28 K),

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41 which compares reasonably well with the value of D / g = 0.14 cm-1 (0.20 K) calculated from the magne tization fit (D = -0.26 cm-1, g = 1.92). -1 -0.5 0 0.5 1 -1-0.500.51 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 0.9 K 1.0 K M/Ms 0H (T) 0.04 K 0.07 T/s -1 -0.5 0 0.5 1 -1-0.500.51 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 0.9 K 1.0 K M/Ms 0H (T) 0.04 K 0.07 T/s -1 -0.5 0 0.5 1 -1-0.500.51 0.280 T/s 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s M/Ms 0H (T) 0.04 Ka) b) -1 -0.5 0 0.5 1 -1-0.500.51 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 0.9 K 1.0 K M/Ms 0H (T) 0.04 K 0.07 T/s -1 -0.5 0 0.5 1 -1-0.500.51 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 0.9 K 1.0 K M/Ms 0H (T) 0.04 K 0.07 T/s -1 -0.5 0 0.5 1 -1-0.500.51 0.280 T/s 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s M/Ms 0H (T) 0.04 Ka) b) Figure 2-12. Magnetization ( M ) vs. magnetic field hysteresis loops for a single crystal of complex 1 MeCN at (a) the indicated temper atures and fixed sweep rate and (b) the indicated sweeping rates at 0.04 K. M is normalized to its saturation value, Ms Complex 2 CH2Cl2Et2O also exhibited hysteresis l oops (Figure 2-13), and their coercivities increase with decreasing temperature and increasing scan rate, confirming that this complex is also an SMM. Be low ~0.2 K, the loops become temperature independent, consistent with ground state QTM as the only relaxation pathway. The loops are overall qualitatively similar to those for 1 MeCN, but have an unusual shape and background slope due to the presen ce of two molecules with di fferent orientations in the unit cell. The field was app lied along the easy axis ( z axis) of one molecule and thus approximately transverse to the easy axis of the other; these field or ientations should give a step-like hysteresis loop and a linear slope , respectively, and a co mbination of the two is thus observed. The steps due to QTM are clearly present but not as sharp and well resolved as those of 1 MeCN, due partly to the two molecular orientations in the cell, but probably mainly to broade ning effects from a distributi on of molecular environments

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42 as a result of the bad disorder of the solvent molecules of crystallization; such a distribution of environments l eads to a distribution of D values and thus a distribution of step positions, leading to broa dening. As a result it becomes di fficult to assess the precise number and position of the steps, and we thus did not attempt to calculate D / g from the hysteresis loops of 2 CH2Cl2Et2O. -1 -0.5 0 0.5 1 -1.2-0.8-0.400.40.81.2 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 0.9 K 1.0 K 1.1 K M/Ms 0H (T) 0.07 T/s -1 -0.5 0 0.5 1 -1.2-0.8-0.400.40.81.2 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s M/Ms 0H (T) 0.04 Ka) b) -1 -0.5 0 0.5 1 -1.2-0.8-0.400.40.81.2 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 0.9 K 1.0 K 1.1 K M/Ms 0H (T) 0.07 T/s -1 -0.5 0 0.5 1 -1.2-0.8-0.400.40.81.2 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s M/Ms 0H (T) 0.04 Ka) b) Figure 2-13. Magnetization ( M ) vs. magnetic field hysteresis loops for a single crystal of complex 2 CH2Cl2Et2O at (a) the indicated temp eratures and fixed sweep rate and (b) the indicated sweeping ra tes at 0.04 K. M is normalized to its saturation value, Ms In order to obtain the actual or effect ive barriers to magnetization relaxation ( Ueff), magnetization vs. time decay data were collect ed at temperatures down to 0.04 K. These data were also obtai ned on single crystals 1 MeCN and 2 CH2Cl2Et2O. First, a large dc field was applied to the sample at ~5 K to saturate its magnetization in one direction, and the temperature was then lowered to a chosen value between 0.04 and 1.07 K. When the temperature was stable, the field was swep t from 1.4 to 0 T at a rate of 0.14 T/s, and then the magnetization in zero field was measur ed as a function of time. This gave a set of relaxation time ( ) vs. T data, which were used to cons truct an Arrhenius plot based on the Arrhenius relatio nship of Eq. 2-9, = 0 exp ( Ueff/kT) (2-9)

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43 where 0 is the pre-exponential term, Ueff is the (mean) effective barrier to relaxation, and k is the Boltzmann constant. These plots for 1 MeCN and 2 CH2Cl2Et2O are presented in Figure 2-14. The fits of the thermally-activated region above 0.5 K, shown as the dashed lines in Figure 2-14, gave Ueff/ k = 11 K and 0 = 7 x 10-7 s for complex 1 , and Ueff/ k = 15.3 K and 0 = 3 x 10-7 s for complex 2 . These values are in the expected range: That for 1 is slightly less than the U va lue of 18.3 K calculated from the magnetization fit parameters, as expected si nce the QTM provides a relaxation short-cut lowering the effective barrier, whereas that for 2 is actually slightly above the U of 14.0 K from the magnetization fits. However, we be lieve this to be an artifact due to the uncertainty inherent in determining D from magnetization fits. 10-11001011020510152025 s 1/T (1/K) = (7 x 10-7) exp(11/T) 10-310-1101103105012345 1/T (1/K) = (3 x 10-7) exp(15.3/T) s a) b) 10-11001011020510152025 s 1/T (1/K) = (7 x 10-7) exp(11/T) 10-11001011020510152025 10-110010110210-11001011020510152025 0510152025 s 1/T (1/K) = (7 x 10-7) exp(11/T) 10-310-1101103105012345 10-310-110110310510-310-1101103105012345 012345 1/T (1/K) = (3 x 10-7) exp(15.3/T) s a) b) Figure 2-14. Relaxation time vs. temperature studies on a single crystal. Plot of relaxation time ( ) vs. 1/ T for complexes 1 (a) and 2 (b). The green solid line is a fit to the Arrhenius equation. See the text for fitting parameters 2.3.4 Computational Studies The exchange interactions parameters in complexes 1 and 2 were determined using both the semiempirical ZILSH method59 and density functiona l theory (DFT). The motivation for these calculations was to obtain the parameters for complex [Mn12(O2CMe)14(mda)8] ( 1 ) which is too large for our standard susceptibility fitting procedures to be applied, and thus to hopefully rationalize the S = 7 ground state. For

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44 [Mn4(O2CPh)4(mda)2(mdaH)2] ( 2 ), we wanted to also compare the J parameters to those obtained from the fit of the variable temper ature magnetic susceptibility. In both cases, wavefunctions for various spin component s were assumed to fit a Heisenberg Hamiltonian with energies given by Eq. 2-10. E = E0 -2 JAB SA SB (2-10) where E0 includes all spin-independent te rms. The exchange parameters JAB were obtained by simultaneous solution usi ng energies and spin couplings SA SB calculated for a number of spin component s equal to the number of parameters. Refined energies were obtained using DFT for several model clusters (vide infra), and substituted into the above Hamiltonian (Eq. 2-10) with spin couplings found with ZILSH. 2.3.4.1 ZILSH and DFT calculations in complex 1 As stated earlier, a fit of the variable te mperature magnetic susceptibility data for 1 is not possible, owing to the large size, so inst ead the exchange interactions within it have instead been obtained by ZILSH and DFT calculations. The more efficient ZILSH method has been applied to the entire comple x. With twelve magnetic centers, there are sixty-six possible exchange cons tants (some of which are zero) plus the spin-independent term E0, so calculations on sixty-seven spin components were needed for simultaneous solution of equations. This number of calcu lations was carried out by considering the high-spin component, where a ll metals are spin-up, and all components in which the spins of two metals have b een reversed. The exchange parameters found by the ZILSH calculation on complex 1 by simultaneous solution were all antiferromagnetic (Table 28). This leads to a ground state spin of S = 3 since the Mn2+ and Mn3+ ions alternate around the ring: The six SA = 5/2 Mn2+ ions are spin-up and the six SA = 2 Mn3+ ions are

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45 spin-down. This is at odds with the ground state spin of S = 7 found from the fit of the magnetization vs . field data, and from the ac susceptibil ity data. It is important to note, however, that the calculated exchange parame ters are all quite small in magnitude, and thus even a small error in their determination could have led to an incorrect sign for some of them. Considering the exch ange interaction between tw o centers to be a sum of ferromagnetic and antiferromagnetic terms,59 if either of these terms is even slightly too large or too small, the resulting sign of the sum of the two term s could be in error. It was thus decided to carry out more accurate DFT calculations to better determine the exchange constants. The entire complex 1 is too large to be considered with DFT, so several smaller model clusters were constructed. The six symm etry-unique metal ions were divided into two clusters of three, the first including Mn6', Mn1 and Mn2 and the second including Mn3, Mn4, and Mn5. In defining these model cl usters, ligands bridging between metals in a particular cluster and t hose in other clusters had to be made terminal. To do so, carboxylate ligands were protonated to give HO2CMe ligands, with the proton added along the line connecting the oxygen and metal out side the cluster at a distance of 1.0 . Secondly, only the oxygen donor site was re tained for mda ligands bridging between different clusters, along with the fi rst carbon atom of the corresponding -CH2CH2chain. The second carbon atom was replaced with a hydrogen atom with a C-H bond distance scaled to 1.1 , giving a MeOligand. In this way, the model clusters had zero charge, as does the parent complex, and a reasonable simulation of the ligand field of each metal was maintained.

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46 With the above-described alterations, Mn3, Mn4, and Mn5 were included in the model complex [MnIIMnIII 2(O2CMe)2(HO2CMe)2(mda)3]. Similarly, Mn6', Mn1 and Mn2 are included in the model complex [MnII 2MnIII(O2CMe)3(HO2CMe)4(OMe)2(mda)]. Finally, the two connections between th ese units, Mn2-Mn3 and Mn5-Mn6, were modeled with the dinuclear complex [MnIIMnIII(O2CMe)(HO2CMe)3(OMe)2(mda)]. Although this formula is identical for the two connections, it is important to note that the structural parameters are not, retaining the same values as those obtained for the Mn2Mn3 and Mn5-Mn6 subunits of complex 1 , respectively. The results of the DFT, and previous ZILS H, calculations are presented in Table 28. The primary difference between these DFT re sults and those found with ZILSH is that the exchange interactions between Mn3Mn4 and Mn4-Mn5 are both ferromagnetic, which can thus lead to a ground state spin value of S > 3. Interestingly, the Mn6'-Mn1 interaction is predicted to be very close to zero by the DFT calculations, and indeed its sign cannot be specified within the uncerta inty of the calculation. Apparently, the ferromagnetic and antiferromagnetic contributio ns to the Mn6'-Mn1 exchange parameter effectively cancel each other out, leading to almost no preference for the spin alignment, i.e. , the J value for Mn6'-Mn1 (and Mn1'-Mn6) is a pproximately zero. In reality, it is very unlikely to be exactly zero, of course, but the DFT calculation cannot by itself identify the true sign of this inter action. The latter requires a complete examination of both the DFT and experimental magnetic data, as provided below. We will ignore the Mn6'-Mn1 and Mn1'-Mn6 interactions for the moment and consider just the resultant spins of the two Mn6 fragments that they couple together and which represent the two halves of the complete Mn12 complex.

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47 Table 2-8. Exchange consta nts computed for complex 1 and various model clusters with ZILSH and DFT methods. The model complexes are described in the text. See figure 2-15 for numbering scheme. All other exchange constants were found to be zero Interaction J , ZILSH, cm-1 ZILSH, model clusters, cm-1 B3LYP, model clusters, cm-1 Mn1-Mn2, Mn1'-Mn2' a -4.5 -5.0 -1.4 Mn2-Mn3, Mn2'-Mn3' a -4.3 -4.2 -4.6 Mn3-Mn4, Mn3'-Mn4' b -0.5 -0.9 +3.5 Mn4-Mn5, Mn4'-Mn5' c -1.2 -1.5 +4.0 Mn5-Mn6, Mn5'-Mn6' c -3.3 -3.4 -2.5 Mn6-Mn1', Mn1'-Mn6' b -2.1 -2.1 +0.0 d a Model complex 3 2 2 2 2 III 2 II) mda ( ) CMe HO ( ) CMe O ( Mn Mn (see text for details) b Model complex [MnIIMnIII(O2CMe)(HO2CMe)3(OMe)2(mda)] (see text for details) c Model complex ) mda ( ) OMe ( ) CMe HO ( ) CMe O ( Mn Mn2 4 2 3 2 III II 2 (see text for details) d Small ferromagnetic value (+0.02 cm-1) found for this parameter Employing the calculated signs of the other J values in the complex (the first five entries in Table 2-8), the resultant spin alignments reveal that each Mn6 fragment will have S = 7/2, as shown in Figure 2-15a. The overall S of the complete molecule is then directly determined by the sign of the remain ing interaction, that between Mn6'-Mn1 and Mn1'-Mn6: (i) If this is negative (antife rromagnetic), the spins of Mn6'-Mn1 and Mn1'Mn6 will be aligned antiparallel, the two S =7/2 fragment spins will be aligned parallel, and the complete molecule will possess a ground state spin of S = 7; all six Mn3+ (S = 2) and two of the Mn2+ (S = 5/2) ions will be spin-up, and the other four Mn2+ ions will be spin-down. (ii) If, on the othe r hand, this interaction is pos itive (ferromagnetic), the spins of the Mn6'/Mn1 and Mn1'/Mn6 pairs w ill each be aligned parallel, the two S =7/2 fragment spins will be aligned antiparallel , and the complete molecule will possess a ground state spin of S = 0 (Figure 2-15b). It is clear from the combined experimental magnetic data described above that complex 1 does not possess an S = 0 ground state, and we therefore conclude that the Mn1-Mn6 and Mn1-Mn6 inte raction is antiferromagnetic and the complex thus possesses an S = 7 ground state. Thus, th e DFT calculations are in

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48 perfect agreement with the experimental magnetization studies , and thus provide independent support for the conclusion that 1 has an S = 7 ground state arising from the spin alignments of Figure 2-15a. Mn6 Mn1' Mn2' Mn3' Mn4' Mn2 Mn3Mn5 Mn4 Mn1 Mn5' Mn6' 2 2 22 2 2 5/2 5/2 5/2 5/2 5/2 5/2 S = 7/2 fragment S = 7/2 fragment Mn6 Mn1' Mn2' Mn3' Mn4' Mn2 Mn3Mn5 Mn4 Mn1 Mn5' Mn6' 2 2 22 2 2 5/2 5/2 5/2 5/2 5/2 5/2 S = 7/2 fragment S = 7/2 fragment Mn6 Mn1' Mn2' Mn3' Mn4' Mn2 Mn3Mn5 Mn4 Mn1 Mn5' Mn6' 2 2 22 2 2 5/2 5/2 5/2 5/2 5/2 5/2 S = 7/2 fragment S = 7/2 fragment Mn6 Mn1' Mn2' Mn3' Mn4' Mn2 Mn3Mn5 Mn4 Mn1 Mn5' Mn6' 2 2 22 2 2 5/2 5/2 5/2 5/2 5/2 5/2 S = 7/2 fragment S = 7/2 fragment a) ST= 7 ST= 0 b) Mn6 Mn1' Mn2' Mn3' Mn4' Mn2 Mn3Mn5 Mn4 Mn1 Mn5' Mn6' 2 2 22 2 2 5/2 5/2 5/2 5/2 5/2 5/2 S = 7/2 fragment S = 7/2 fragment Mn6 Mn1' Mn2' Mn3' Mn4' Mn2 Mn3Mn5 Mn4 Mn1 Mn5' Mn6' 2 2 22 2 2 5/2 5/2 5/2 5/2 5/2 5/2 S = 7/2 fragment S = 7/2 fragment Mn6 Mn1' Mn2' Mn3' Mn4' Mn2 Mn3Mn5 Mn4 Mn1 Mn5' Mn6' 2 2 22 2 2 5/2 5/2 5/2 5/2 5/2 5/2 S = 7/2 fragment S = 7/2 fragment Mn6 Mn1' Mn2' Mn3' Mn4' Mn2 Mn3Mn5 Mn4 Mn1 Mn5' Mn6' 2 2 22 2 2 5/2 5/2 5/2 5/2 5/2 5/2 S = 7/2 fragment S = 7/2 fragment a) ST= 7 ST= 0 b) Figure 2-15. a) Depiction of the spin alignments in the S = 7 ground state of complex 1 as predicted by the DFT calculations. b) Depiction of the spin alignments in the S = 0 ground state of complex 1. See text for explanation The S = 7 and S = 0 states must be virtually de generate, however, given that the Mn6'-Mn1 and Mn1'-Mn6 exchange parameter is nearly zero. Bo th states would then be thermally populated at any appreciable temperat ure, but even if they were degenerate, the spin degeneracy of the S = 7 state would give it a larg er population according to the Boltzmann distribution. It should be added that the signs of the ex change parameters listed in Table 2-8 are consistent with those in the literature for dinuclear MnIIMnIII complexes. These complexes have very similar bridging ligand set and they are compared in Table 2-9. They have either two phenoxide oxygen atoms (together with one ha lide ion in the first two complexes) or one phenoxide oxygen at om with two acetate s (the other three complexes).

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49 Table 2-9. Magnetic exchange parameters for phenoxo bridging gr oups of binuclear MnIIMnIII complexes Complex J, cm-1 [LMn2Br3] a -1.0 [LMn2Cl2Br] a -1.7 [MnIIMnIII(bpy)2(biphen)2(biphenH)] b +0.89 [MnIIMnIII(bcmp)(-OAc)2](ClO4)2 c -7.7 [MnIIMnIII(bpmp)(-OAc)2](ClO4)2 d -6.0 a L2ion is the dianion of the Schiff base c ondensation of 2 mol 1, 3-diaminopropane and 2 mol of 2,6-diformyl-tert-butylphenol b bpy is 2, 2'-bipyridine, and biphenH2 is 2,2'-biphenol c bcmp is 4-methyl-2,6-bis(1,4,7-triazacyclononane)phenol c bpmp is 4-methyl-2,6-bis (pyridylmethylamine)phenol In general, the exchange parameters for dinuclear MnIIMnIII complexes are very weak and either side of zero, but it is known that such complexes with two bridging phenoxide groups give ferromagnetic coupling, pr esumably as a result of the smaller MnO-Mn angles resulting fro m having two monoatomic bridges between the Mn ions.60 It is thus consistent with previous literature examples that the Mn4-Mn5, Mn4-Mn5, Mn3Mn4, and Mn3-Mn4 interactions in Table 2-8 should be ferromagnetic, since these Mn2 pairs each possess two monoatomic alkoxide bridges (and one triatomic carboxylate bridge), whereas the other Mn2 pairs possess either one mono atomic alkoxide bridge or both monoatomic alkoxide and carboxylate brid ges (plus triatomic carboxylate bridges). 2.3.4.2 ZILSH calculation and magnetic su sceptibility fits for complex 2 Exchange interactions in [Mn4(O2CPh)4(mda)2(mdaH)2] (2) were modeled assuming a set of spin states with energies defined by the He isenberg Hamiltonian (Eq. 210), where the exchange constants JAB were fit to reproduce the variable temperature magnetic susceptibility data fit of Figure 2-8. A generic algo rithm method described earlier61 was used for this purpose. Briefly, the method uses the Van Vleck equation57 to relate the product MT to the exchange constants and g factor. Contributions from each

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50 spin state are Boltzmann-weighted at each temperature considered. Additionally, a temperature-independent paramagnetism of 400 10-6 cgs units was included, as well as a static contribution from 0.2 mol% of a S = 5/2 magnetic impurity assumed to be present in the sample. The exchange constants and g factor were adjusted simultaneously to minimize the differences between expe rimental and calculated values of MT for temperatures above 20 K. Lowe r temperatures were excluded because minor effects not considered in the model, such as zero-field splitting and intermolecular interactions, become operative below 20 K. Complex 2, (MnII 2MnIII 2) is expected to have thre e distinct non-zero exchange interactions within the Mn4 ‘butterfly’ core, indicated as Jbb, Jwb, and J'wb. As we stated earlier, Jwb and J'wb are inequivalent by symmetry but were taken as identical for the analysis by the Kambe vector coupli ng method. This inequivalence of Jwb, and J'wb was however observed in the study of th e related butterf ly complex [Mn4O2(O2CPh)6(dpm)2] by the sensitive inelastic ne utron scattering technique.63 An additional interaction (Jww) between the two ‘wingtip’ ions Mn2 and Mn2' was included the fit of the susceptibility data (Figure 2-16). Mn1 Mn2 Mn1 Mn2 JwbJwbJ wbJwb Jbb JwwMn1 Mn2 Mn1 Mn2 JwbJwbJ wbJwb Jbb Jww Figure 2-16. Schematic diagram of metal framework for complex 2, showing the exchange constants considered The values of the parameters obtained from the fit were Jbb = +95.15 cm-1, Jwb = +1.59 cm-1, J'wb = +0.48 cm-1, Jww = -0.44 cm-1, and g = 1.888. The result of the fit is

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51 compared to the experimental values of MT in Figure 2-17. These parameters predict a ground state spin of S = 9, consistent with the experimental magnetic studies. 15 17 19 21 23 25 27 29 0.025.050.075.0100.0125.0150.0175.0200.0225.0250.0275.0300.0 Temp (K)mT Figure 2-17. Comparison of calculated and e xperimental variable temperature magnetic susceptibility of complex 2. The calculated curve used the exchange constants, g factor, TIP, and percent magne tic impurity given in the text The weak values of Jwb and J'wb found for complex 2 are consistent with those found for the similar complex [Mn4(O2CMe)2(pdmH)6]2+ (pdmH2 = pyridine-2,6dimethanol), where Jwb = J'wb = 0.40 cm-1,17 and for Mn(II)-Mn(II I) interactions in general, which are known to be weak and either antiferromagnetic or ferromagnetic.17a The value found for Jbb of 95 cm-1 is much larger than that found for [Mn4(O2CMe)2(pdmH)6]2+ (Jbb = 8.1 cm-1), and more generally is quite large for Mn(III)Mn(III) interactions, which are typically weak.19 This could arise from the smaller Mn-OMn bridging angle in complex 2 compared to that in the pdm complex, 97.80 versus 100.30. Though caution must be used in correlati ng exchange constants with structural parameters, particularly when the ligands are distinctly different,64 it is well-established that small angles approaching 900 favor ferromagnetic coupling, all else being the

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52 same.65-67 The ligands in complex 2 and the pdm complex are similar enough that such a dependence on angle is reasonable to assume. Given also that the coupling can change from ferromagnetic to antiferromagnetic with differences in angle on the order of three degrees in structurally re lated complexes (e.g., hydr oxide bridged dicopper(II) complexes68 and oxide-bridged diferric complexes69), the reduction in angle seen in complex 2 could contribute to the large value of Jbb that was found. Given the surprisingl y large value of Jbb found in the fit, the effect of changes in Jbb on the error of the fit was considered in more detail. In doing so, th e error was taken as simply the sum of the absolute values of the differences between calculated and experimental values of MT over all temperatures above 20 K, and all parameters other than Jbb were held fixed at the values given a bove. The results are shown in Figure 2-18 for values of Jbb ranging from 50 cm-1 to 150 cm-1. As the figure shows, the error becomes almost constant for Jbb > 80 cm-1, and increases rapidly as the value is reduced below 80 cm-1. Several attempts were made to obtain a fit with Jbb constrained to smaller values, without success. Together , these results indicate that Jbb is ferromagnetic with a value above 80 cm-1, but the fit does not give a more sp ecific value. Regardless of the exact value of Jbb, though, all nonzero exchange c onstants are predicted to be ferromagnetic for complex 2, leading to a gr ound state with S = 9. It is interesting to note that the J values obtained from the calculations (Jbb = +95.15 cm-1, Jwb = +1.59 cm-1, J'wb = +0.48 cm-1, Jww = -0.44 cm-1, and g = 1.888) are reasonably consistent with those from th e dc magnetic susceptibility fit assuming C2V symmetry (Jbb = +41 cm-1, Jwb = +1.6 cm-1, Jww = -0.7 cm-1, g = 1.79), which employed the Kamb approach52. In both cases, the Jbb is much stronger than Jwb (and J'wb), the

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53 latter is (are) near zero, and a small antiferromagnetic Jww is indicated (note that in both cases, our models have ignored single-ion anisotropy effects). 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 50.060.070.080.090.0100.0110.0120.0130.0140.0150.0 Jbb (cm-1, -2J convention)Error (equation x) Figure 2-18. Error in fit of variable temperature magnetic susceptibility of complex 2 versus Jbb. See text for details The ZILSH results that we re obtained for complex 2 are all in agreement with the magnetic studies, leading to a calculated ground state spin of S = 9. 2.4 Conclusions The belief that a N,O,O-chelate that is more flexible than the similarly N,O,Ochelate pdm2(pdmH2 = pyridine-2,6-dimethanol) might l ead to distinctly different Mn complexes has turned out to be the case. The use of mdaH2 in reactions with Mn sources has led to three new complexes of different nuclearities, all of them mixed-valent MnIII/MnII species, and two of them have been identified as new members of the SMM family. The Mn12, complex 1, is of particular interest, be ing a very rare example of a SMM with a loop structure. It appears at first glance pa radoxical that the magnetic properties of this species are controlled by the weakest exchange interaction in the

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54 molecule, determining wh ether the ground state is S = 0 or 7, but of cour se this is in fact logical for a loop structure where th ere are no competing interactions. The Mn4 complex has been studied by DF T and ZILSH calculations, which provided a further confirmation of the ground state spin obtained by magnetic susceptibility measurem ents. Although the Mn6 complex is not an SMM, it is the initial example of a complex obtained using mdaH2, and containing oxi de and hydroxide bridges. Mn6 is aesthetically appeali ng and represents a new stru ctural type in manganese chemistry. Thus, the use of mdaH2 has proven to be a successful approach to obtain mixedvalent Mn(II)/Mn(III) clusters. The presence of Mn(III) ions give anisotropy to the molecules, whereas Mn(III) and Mn(II) both cont ribute to the high-spin of the molecule. Hence mdaH2 seems to be a nice ligand to obtai n new SMMs. Therefore, manganese chemistry with mdaH2 is further being explored and mi ght lead to new and better singlemolecule magnets with higher energy barriers.

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55 CHAPTER 3 HIGH NUCLEARITY IRON AND NICKEL COMPLEXES: [Fe22O14(OH)3(O2CMe)21(mda)6](ClO4)2 AND [Ni24(O2CMe)42(mdaH)6(EtOH)6] INCORPORATING N-METHYLDIETHANOLAMINE (MDAH2) 3.1 Introduction There are numerous motivations for the re search efforts devoted to the synthesis and study of polynuclear 3d metal clusters by various groups around the world. Among these is the search for oxide-bridg ed metal clusters that model Mx sites in biomolecules. Such research could lead to a better unders tanding of the method of FeO core growth in ferritin or even a functional biomimetic of the Mn-containing mol ecule responsible for the oxidation of water to oxygen gas within the phot osynthetic apparatus of green plants and cyanobacteria.72 In addition, polynucle ar 3d metal clusters of ten display interesting and occasionally novel magnetic propertie s, including high ground state spin (S) values, currently up to S = 83/2,73 and single-molecule magnetism behaviour.74, 55 The latter results when a molecule possesses both a large ground state spin and a significant magnetic anisotropy of the Ising (or easy axis) type, as reflecte d in a negative zero-field splitting parameter (D). Like Mn(III), which serves as the pr imary source of magnetic anisotropy in numerous single-molecule magnets (SMMs), Ni (II) is a particularly attractive starting material for the construction of polynuclear complexes whic h may potentially behave as SMMs given its large single-i on anisotropy. The anisotropy of a cluster arises from the anisotropy of its constituent metal centers, and depends on the relative orientations of their magnetic axes. However, desp ite |D| values greater than 10 cm-1 of several

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56 representative mononuclear Ni(II) complexes,75, 76 only a few Ni(II) clusters have been shown to exhibit SMM beha vior. These include [Ni12(chp)12(O2CMe)12(THF)6(H2O)6]17d (chp = 6-chloro-2-pyridonate), [Ni(hmp)(ROH)Cl]4 77 (Hhmp = 2hydroxymethylpyridine), [Ni(H2thme)(MeCN)]4(NO3)4]78 (H3thme = 1,1,1trihydroxymethylethane), [Ni21(cit)12(OH)10(H2O)10]Na2(NMe4)14]79 (cit = citrate anion), and [Ni8Na2(N3)12(tBuPhCO2)2(mpo)4(Hmpo)6(EtOAc)6]80 (Hmpo = 2methylpyrazolinone), [Ni10(tmp)2(N3)8(acac)6(MeOH)6]81 (H3tmp = 1,1,1tris(hydroxymethyl)propane; acac = acetylace tonate). These findings emphasize the significant difference between magnetic anisotropies of monomeric and polynuclear Ni(II) complexes, but stress the potential for interesting magnetic behavior in such polynuclear clusters. Not only is Ni(II) attractive for its potent ial contribution to the magnetic anisotropy of a complex, but it can also be manipul ated through the use of various synthetic strategies to give ferroma gnetic coupling betwee n metal centers a nd a nonzero ground state spin. Ferromagnetic coupling is freque ntly observed between nickel ions in complexes with hydroxo, oxo and azide bridges, and such exchange interactions have been studied in detail. In [Ni4O4]4+ cubane complexes,82 it has been shown that the magnetic behavior is related to the Ni-O-Ni angle, with the interaction between metal centers being ferromagnetic when the angle is close to 90 83 and antiferromagnetic when the angle is greater than ca. 101.84 In contrast, in azide-bridged Ni complexes, the exchange interactions have b een rationalized in the end-to -end and end-on coordination modes, in most cases giving antiferroma gnetic coupling and ferromagnetic coupling, respectively.85

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57 In addition to our interest in Ni(II) salts for the preparation of polynuclear clusters, Fe(III) compounds also serve as attractive starting materials for similar reactions. Although interactions between Fe (III) ions are generally antiferromagnetic, some clusters experience spin frustration or display particular Fex topological arrangements that can result in ground states with reasonably large spins. In favor able cases wher e these large spin ground states are coupled with a significant magnetic anisotropy, the compounds can behave as SMMs. The most well-studied iron SMM are [(Fe8O2(OH)12(tacn)6)Br7H2O]Br8H2O (tacn=1,4,7-triazcyclononane)86 and [Fe4(OMe)6(dpm)6] (Hdpm = dipivaloylmethane).74 Considerable efforts spanning many years in the area of 3d metal cluster chemistry have been invested in the exploration of different synt hetic strategies towards the preparation of high nuclearity clusters, resulting in several empirically established approaches to a variety of species. In Fe chem istry, for example, alcoholysis of iron salts in the presence of carboxylate groups, with or without chelat ing ligands, has proven to be a very useful method for obtaining bo th oxo and hydroxo-cont aining clusters.87, 88 Another approach is the use of chelates containing alcohol groups, since their alkoxide arms are good bri dging groups, fostering the formation of polynuclear products.89 Our efforts to date with alcohol-contai ning chelates have been concentrated primarily in the area of manganese chemistr y, and gave our prev ious success with mdaH2.90 We have now extended ou r exploration of such r eactivity to both iron and nickel, namely the reactions of salts of these metals with N-methyldiethanolamine (mdaH2).

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58 3.2 Experimental 3.2.1 Syntheses All manipulations were performed under aerobic conditions us ing materials as received, except where otherwise noted. [Ni24(O2CMe)42(mdaH)6(EtOH)6] (4). To a green stirred solution of Ni(O2CMe)2H2O (0.50 g, 2.00 mmol) in EtOH/MeCO2H (3:1 v/v) (40 mL) was added mdaH2 (76 L, 0.62 mmol). Crystals of complex 4 suitable for X-ray crystallography were obtained upon slow diffusi on of the solution with Et2O/MeCO2H (10:1 v/v). They were collected by filtration, washed with Et2O (3 x 10ml), and dried in air. The yield was ~25 %. Elemental analysis for [Ni24(O2CMe)42(mdaH)6(EtOH)6]20H2O (C126H274N6Ni24O128): Experimental (calculated): C, 28. 39; H, 5.18; N, 1.58 %. Found: C, 28.67; H, 5.26; N, 1.84 %. Se lected FT-IR data (KBr, cm-1): 1709 (s), 1582 (s), 1417 (s), 1342 (s), 1265 (m), 1053 (m), 1025 (m), 942 (w ), 908 (m), 881 (m), 682 (m), 617 (w), 450 (w). [Ni(mdaH2)2](O2CMe)2 (5). To a green stirred solution of Ni(O2CMe)24H2O (0.10 g, 0.40 mmol) and mdaH2 (46 L, 0.40 mmol) in Et OH (30 mL) was added NEt3 (56 L, 0.40 mmol). After several days , blue crystals of complex 5 were suitable for X-ray crystallography, they were obtained upon slow diffusion of th e solution with Et2O. washed with Et2O (15ml), and dried in air. The yiel d was 60 %. Elemental analysis for [Ni(mdaH)2](O2CMe)2H2O (C14H36N2NiO10): Experimental (calcu lated): C, 37.27; H, 8.04; N, 6.21 %. Found: C, 37.32; H, 7.91; N, 6.51 %. Selected FT-IR data (KBr, cm-1): 1889 (s), 1541 (s), 1408 (s), 1344 (s), 1196 (w ), 1149 (s), 1059 (m), 1021 (m), 998 (s), 906 (m), 883 (s), 758 (s), 651 (s), 610 (m), 554 (m), 479 (m), 402 (m).

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59 [Fe22O14(OH)3(O2CMe)21(mda)6](ClO4)2 (6). To a stirred solution of FeCl3H2O (0.30 g, 1.10 mmol) and Na(O2CMe)2 (0.60 g, 7.30 mmol) in EtOH (10 mL) was added mdaH2 (0.14 mL, 1.20 mmol). The color of the mixture rapidly changed from yellow to orange. To the reaction mixture was added NaClO4 (70 mg, 5.70 mmol), and the resulting solution was allowed to evaporate slowly in air under ambient conditions. Red-orange crystals of 6 formed slowly over two weeks. The latter were collected by filtration and redissolved in CH2Cl2 (20 mL). Diffusion of Et2O into the CH2Cl2 solution slowly produced crystals that were suitable for X-ray crystallography. These were maintained in contact with the mother liquor to prevent the loss of inters titial solvent. The yield was ~67 %. Elemental analysis for [Fe22O14(OH)3(O2CMe)21(mda)6](ClO4)2H2O (C72H140N6Fe22O83Cl2): Experimental (calculated): C, 23.26; H, 3.80; N, 2.26 %. Found: C, 23.55; H, 3.75; N, 2.00 %. Selected FT-IR data (KBr, cm-1): 1576 (s), 1540 (s), 1436 (s), 1351 (w), 1096 (m), 1025 (w), 999 (w), 903 (w), 667 (m), 654 (w), 623 (w), 583 (m), 538 (w), 419 (w). 3.2.2 X-Ray Crystallography Data were collected at 173 K on a Si emens SMART PLATFORM equipped with a CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Suitable single crystals of 4H2O6MeCO2H12EtOH12Et2O, 5 and 6H2O4EtOH4Et2O were separately attached to a glass fiber using silicone grease and transferred to the goniostat wher e they were cooled to 173 K for characterization and data collection. Cell parameters were refined us ing up to 8192 reflections. A full sphere of data (1850 frames) was collected using the -scan method (0.3 frame width). The first 50 frames were re-measured at the end of data collection to monitor instrument and

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60 crystal stability (maximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces. Each structure was solved by direct methods (SHELXTL)91 and standard Fourier te chniques, and was refined using full-matrix least-squares methods . All non-hydrogen atoms were refined anisotropically, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. The solvent molecules were significantly disordered and could not be modeled properly. Hence, the program SQUEEZE,32 a part of the PLATON33 package of crystallographic software , was used to calculate the solvent disorder area and remove its contribution to the overall intensity data. Refinements were done using F2. Complex 4H2O6MeCO2H12EtOH12Et2O crystallizes in the cubic space group 3 I ab . The asymmetric unit consists of 1/6 of the Ni24 ring, two H2O molecules (one of which is situated at the ce nter of the ring), one MeCO2H, two EtOH and two Et2O molecules. The EtOH ligand (C1, C2 and O1 ) on Ni4 is disordered and was refined in two parts with their site occupation factors dependently refined. The protons on O1 and O1’ were refined but their thermal parameters were derived from their parent atoms. O10 is also protonated; its H atom was located on a difference Fourier map and refined freely. A total of 386 parameters were refined in the final cycle of refinement using 6946 reflections with I > 2(I) to yield R1 and wR2 of 3.98% and 9.76%, respectively. Complex 5 crystallizes in th e monoclinic space group P 21/ c , and the asymmetric unit consists of a half complex and one MeCO2 anion. Both of the hydroxyl protons (atoms H1 and H2) on O1 and O2, respectively, form hydrogen bonds with O3 and O4 of the MeCO2 anion. A total of 157 parameters were refined in the final cycle of

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61 refinement using 5833 reflections with I > 2(I) to yield R1 and wR2 of 3.30% and 8.03%, respectively. A preliminary search of reciprocal space for 6H2O4EtOHEt2O revealed a set of reflections with a monoclinic lattic e. An initial choice of the space group C 2 /c was subsequently confirmed by the successful solu tion of the structure. The asymmetric unit consists of the Fe22 cluster, two ClO4 anions, four H2O, four EtOH and four Et2O molecules. Charge balance considerations re quire a +2 charge on the cluster to counter the two ClO4 anions in the asymmetric unit, a nd after bond valence sum calculations on both metals and ligands and close examinati on of the bond lengths, it was concluded that there is a proton situated on O28. Table 3-1. Crystallographic data for complexes 4H2O6MeCO2H12EtOH12Et2O, 5 and 6H2O4EtOH4Et2O Parameter 4 5 6 formulaa C210 H464 N6 Ni24 O163C14 H32 N2 Ni O8 C96 H202 Cl2 Fe22 N6 O91 fw, g mol-1 7090.54 415.13 4196.24 space group 3 I ab P 21/ c C 2/ c a , 38.9497(6) 7.9934(6) 29.719(3) b , 38.9497(6) 8.4975(6) 35.321(4) c , 38.9497(6) 14.1043(10) 30.651(3) , deg 90 90 90 , deg 90 95.378(2) 98.367(2) , deg 90 90 90 V , 3 59089.8(16) 953.80(12) 31832(6) Z 8 2 8 T , K 173(2) 173(2) 173(2) radiation, b 0.71073 0.71073 0.71073 calc, g cm-3 1.571 1.445 1.751 R 1 ( wR 2), %c , d 3.98 (9.76) 3.30 (8.03) 6.80 (15.81) a Including solvent molecules. b Graphite monochromator. c R 1 = || Fo| – | Fc|| / | Fo|. d wR 2 = [w ( Fo 2 Fc 2)2] / [ w Fo 2)2]]1/2 where S = [[ w ( Fo 2 – Fc 2)2] / ( n p )]1/2, w = 1/[2( Fo 2) + ( m * p )2 + n * p ], p = [max( Fo 2, 0) + 2* Fc 2]/3, and m and n are constants This proton could not be located in a di fference Fourier map, however, and it was not included in the final refinement. A total of 1618 parameters were refined in the final

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62 cycle of refinement on F2 using 7571 reflections with I > 2(I) to yield R1 and wR2 of 6.80% and 15.81%, respectively. The crystallographic data and structure re finement details for all the compounds are collected in Table 3-1. 3.3 Results and Discussion 3.3.1 Syntheses The reactivity of Ni(II) with the tris-c helating ligand N-methyldiethanolamine (mdaH2) was explored under a variety of conditions (different ratios Ni(II)/mdaH2, i.e. , 1:1, 1:2, 0.1:1; and different solvents and/or mixtures of solvents (i.e., H2O/MeCN, EtOH/MeCN) using a number of Ni(II) salts, as Ni(ClO4)2, NiNO3 and NiCl2. A large majority of our efforts were ineffective, wi th crystallization attempts being unsuccessful. However, from the the reaction of three equivalents of Ni(O2CMe)2•4H2O with one equivalent of mdaH2 in 3:1 solvent mixture of EtOH and MeCO2H, we isolated the new complex [Ni24(O2CMe)42(mdaH)6(EtOH)6] (4) in 24% yield. Crystals of 4 suitable for Xray crystallography were obtaine d by slow diffusion of the reaction solution with 10:1 Et2O/MeCO2H. The reaction yield varies with the ratio of EtOH to MeCO2H, with the yield being optimized with 3:1 EtOH/MeCO2H. The formation of 4 is summarized in Eq. 3-1. 24 Ni(O2CMe)2 + 6 mdaH2 + 6 EtOH [Ni24(O2CMe)42(mdaH)6(EtOH)6] + 6 MeCO2H (3-1) Complex 4 is insoluble in most common or ganic solvents, rendering reactivity studies difficult. Hence, new s ynthetic strategies to obtain soluble products incorporating the mdaH2 ligand were explored. One such strategy th at has proven to be very fruitful to this end is the substitution of PhCO2 for MeCO2 ligands in a compound. Reaction

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63 systems incorporating benzoate were therefor e studied. The obvious substitution is that of Ni(O2CPh)2 for Ni(O2CMe)2 in Eq. 3-1. Ni(O2CPh)2 is not commercially available however, and we used NiCl2H2O and NaO2CPh in lieu of this, following the strategy that has already proven successf ul in manganese chemistry.90 From these reactions blue precipitates containing starting material were obtained. As the addition of an acid helps the form ation of a high nuclearity complex, we explore the reaction with the a ddition of an organic base, NEt3. The reaction of one equivalent of Ni(O2CMe)2•4H2O, one equivalent of mdaH2, and one equivalent of Et3N affords a blue solution. Slow diffusion of this solution with Et2O gives blue crystals of the mononuclear complex [Ni(mdaH2)2](O2CMe)2 (5). A reaction ratio of Ni(O2CMe)2:mdaH2:Et3N of 1:2:2 or 1:4:4 also affords complex 5. Additionally, the reactivity of Fe(III) salts with mdaH2 was studied, and the results obtained are presented. Prev ious studies showed a rational design of various sixmembered iron coronands, reacti ng N-alkyldiethanolamine RN(CH2CH2OH)2 and iron chloride (FeCl3).91 Introduction of carboxylat es in that system was thought to change the structure and study and compare the magnitude and nature of the interactions in polynuclear complexes. The addition of one equivalent of mdaH2 to a reaction solution of one equivalent of FeCl3 and six equivalents of NaO2CMe in EtOH resulted in a color change of the solution from yellow to orange. No crystals can be obtained from the reaction system, so one equivalent of a counterion source, NaClO4, was added to the solution. The solution was allowed to stand undisturbed and after fifteen days afforded red-orange crystals of [Fe22O14(OH)3(O2CMe)21(mda)6](ClO4)2 (6). The crystals were collected by filtration,

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64 dissolved in CH2Cl2 and recrystallized with Et2O. The resulting crystals were suitable for X-ray crystallography. The formation of 6 is shown in Eq. 3-2. 22 FeCl3 + 21 NaO2CMe + 6 mdaH2 + 2 NaClO4 + 17 H2O [Fe22O14(OH)3(O2CMe)21(mda)6](ClO4)2 + 23 Na+ + 43 H+ + 66 Cl+ 17 e(3-2) Complex 6 is the biggest iron cluster known to da te. Further studies of this reaction system were studied and they will be discussed in the following chapter. 3.3.2 Description of Structures 3.3.2.1 Structure of [Ni24(O2CMe)42(mdaH)6(EtOH)6] (4) Complex 4H2O6MeCO2H12EtOH12Et2O crystallizes in the cubic space group 3 I ab . The asymmetric unit consists of 1/6 of the Ni24 ring cluster with four nickel ions, one molecule of ethanol, seven acetates and one mdaHligand. As solvent of crystallization there are two water molecules (o ne of which is at the center of the ring), one acetic acid, two ethanol and two ether molecules. The structure is shown in Figure 31a, together with the cell asymmetric unit, [Ni4(O2CMe)7(mdaH)(EtOH)] (Figure 3-1b), selected metric parameters are listed in Table A-4. The complex consists of a Ni18 loop to which are connected six additional Ni (II) atoms (atoms Ni1). Only [Ni34Se22(PPh3)10] is a higher-nuclearity homometallic Ni cluster.92 All Ni atoms are six-coordinate with distorted octahedral geom etry. The mono-deprotonated 1; 1; 3; 3 mdaHgroups chelate to the external Ni1 at om, with their protonated alcohol arm (O5) bound terminally to Ni1, and their deprotonated alkoxide arm (O6) triply bridging Ni1/Ni2/Ni4.

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65 Ni3 Ni4 Ni2 Ni3 Ni1 N1 O5 O3 O1 O6 O17 O16 O9 O8 O7 O4 O2 O10 O11 O12 O13 O15 O14 C1 C2 Ni3 Ni4 Ni2 Ni3 Ni1 N1 O5 O3 O1 O6 O17 O16 O9 O8 O7 O4 O2 O10 O11 O12 O13 O15 O14 C1 C2a) b) Ni3 Ni4 Ni2 Ni3 Ni1 N1 O5 O3 O1 O6 O17 O16 O9 O8 O7 O4 O2 O10 O11 O12 O13 O15 O14 C1 C2 Ni3 Ni4 Ni2 Ni3 Ni1 N1 O5 O3 O1 O6 O17 O16 O9 O8 O7 O4 O2 O10 O11 O12 O13 O15 O14 C1 C2a) b) Figure 3-1. a) ORTEP representation in PovRay format of the complex 4; b) ORTEP representation in PovRay format of the asymmetric unit of the complex 4: [Ni4(O2CMe)7(mdaH)(EtOH)]. Ni green; O re d; N blue; C gray. Hydrogen atoms have been omitted for clarity Additional bridges between Ni atoms are pr ovided by acetate groups in a variety of coordination modes: mono-atom ically bridging Ni1/Ni3, w ith the unbound O atom (O3) forming a weak hydrogen bond with the OH of the terminal EtOH molecule on Ni1 (O3O1 = 3.1 ); the common syn, syn, 1; 1; mode bridging Ni2/ Ni3 and Ni3/Ni4; the rare syn, syn, anti, 1; 2; 3 bridging Ni1/Ni2/Ni3, Ni2/ Ni4/Ni3 and Ni/Ni2/Ni4; and syn, syn, anti, 1; 2; bridging between Ni3/Ni4. Also, the complex can be described as four polyhedra sharing edges through O12/O6, O6/O2 and O10/O7 and every four pol yhedra are connected to the next four by O14 (Figure 3-2b). The repeat of this asymmetric unit six times over as given by the cubic space group produces the aesthetically pleasing Ni24 complex.

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66 Ni3 Ni4 Ni2 Ni3 Ni1 N1 O5 O3 O1 O6 O17 O16 O9 O8 O7 O4 O2 O10 O11 O12 O13 O15 O14 C1 C2 Ni3 Ni4 Ni2 Ni3 Ni1 N1 O5 O3 O1 O6 O17 O16 O9 O8 O7 O4 O2 O10 O11 O12 O13 O15 O14 C1 C2a)b) Ni3 Ni4 Ni2 Ni3 Ni1 N1 O5 O3 O1 O6 O17 O16 O9 O8 O7 O4 O2 O10 O11 O12 O13 O15 O14 C1 C2 Ni3 Ni4 Ni2 Ni3 Ni1 N1 O5 O3 O1 O6 O17 O16 O9 O8 O7 O4 O2 O10 O11 O12 O13 O15 O14 C1 C2a)b) Figure 3-2. a) ORTEP represen tation in PovRay format of the asymmetric unit of 4; [Ni4(O2CMe)7(mdaH)(EtOH)], b) representati on of the a) by polyhedra. Ni green; O red; N blue; C gray. Hydrogen atoms have been omitted for clarity Charge balance considerations require the Ni ions to be in the +2 oxidation state, and terminal O1 and O5 likely to be prot onated. Bond valence su m calculations confirm these assignments (BVS: O1 = 1.149; O5 = 1.175). 3.3.2.2 Structure of [Ni(mdaH2)2](O2CMe)2 (5) Complex 5 crystallizes in the monoclinic space group P 21/c. The asymmetric unit consists of a half complex and one acetate ani on, and the Ni center is nearly octahedral (Figure 3-3). Selected metric parameters are li sted in Table A-5. The four equatorial sites are occupied by the four O atoms of the mdaH2 ligand (O1, O2), and all are protonated (BVS: O1= 1.149; O2=1.175), forming a hydrogen bond with O3 and O4 of the acetate anion (O1O3 = 2.6 ).

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67 Ni1 N1 N1' O1 O3 O2 O4 O1' O2' O3' O4' Ni1 N1 N1' O1 O3 O2 O4 O1' O2' O3' O4' Figure 3-3. ORTEP representation in PovRay format of complex 5. Ni green; O red; N blue; C gray. Hydrogen atoms have been omitted for clarity 3.3.2.3 Structure of [Fe22O14(OH)3(O2CMe)21(mda)6](ClO4)2 (6) Complex 6H2O4EtOH4Et2O crystallizes in the monoclinic space group C 2/ c , The asymmetric unit consists of the Fe22 cluster, two ClO4 ions, and four H2O, four EtOH and four Et2O solvent molecules of crysta llization. The structure of 6 (Figure 3-4) is unprecedented and consists of twenty-two Fe (III) ions arranged in three sub-units; this is the largest homometallic Fe cluster to date . Selected metric para meters are listed in Table A-6. In the structure, there is a central [Fe4( 3-OH)2( 4-O)2]6+ cubane (Fig. 3-5), whose hydroxide O atoms are O32 and O34, to which are attached two penta-coordinated Fe(III) ions, Fe9 and Fe14. This resultant Fe6 sub-unit is sandwiched between two identical Fe8 units (Fig. 3-6), the linkages being vi a oxide bridges. With the exception of Fe9 and Fe14, all Fe atoms are six-coordina te with distorted oc tahedral geometry.

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68 Figure 3-4. ORTEP representation in PovRay format of complex 6. Fe yellow; O red; N blue; C gray. Hydrogen atoms have been omitted for clarity The complete [Fe22]2+ cation would have virtual tw ofold symmetry except that there is an interesting asymmetry in the centre, best seen in Figure 3-5, with the Fe9/Fe10 pair bridged by the third hydr oxide ion (O28) whereas th e corresponding Fe13/Fe14 pair on the other side is bridged by an acetate group in the same syn, syn 1; 1; -mode as the other acetate groups. Despite th is asymmetry, the core can also be described by three tetrahedra sharing two faces along Fe10/ Fe11/ Fe12 and Fe11/ Fe12/ Fe13 (Figure 3-5b). Fe10 Fe13 Fe11 Fe12 Fe9 Fe14 O35 O29 O28 O34 O32 Fe10 Fe13 Fe11 Fe12 Fe9 Fe14 O35 O29 O28 O34 O32 a) b) Fe10 Fe13 Fe11 Fe12 Fe9 Fe14 O35 O29 O28 O34 O32 Fe10 Fe13 Fe11 Fe12 Fe9 Fe14 O35 O29 O28 O34 O32 Fe10 Fe13 Fe11 Fe12 Fe9 Fe14 O35 O29 O28 O34 O32 Fe10 Fe13 Fe11 Fe12 Fe9 Fe14 O35 O29 O28 O34 O32 a) b) Figure 3-5. a) ORTEP representa tion in PovRay format of the central unit of complex 6; b) representation of the cen tral unit by tetrahedra. Fe yellow; O red. Hydrogen atoms have been omitted for clarity

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69 The central [FeIII 4O2(OH)2] cubane is a very rare unit at this oxidation level. Some Fe/O cubanes containing FeII or mixed FeII/III cores are known, but there is only one FeIII 4O4 cubane reported in the literature.93a Similarly, the end Fe8 units have only been previously observed on one occasion. These units have a three-blade propeller topology with the Fe2/Fe7 vector being the axle, and they ar e bridged by three 4-O2ions O1, O6 and O7, which also connect to the Fe1/Fe5, Fe4/Fe6 and Fe3/Fe8 blades, respectively. Additional O atom bridges between Fe2 pairs are provided by the alkoxide arms of mda2groups, which bind in a 2; 1; 2; 3 fashion. This Fe8 propeller structure is overall very similar to that of [Fe8O3(O2CPh)9(tea)(teaH)3] (teaH3 is triethanolamine).93b Another view of this unit of the structure can be observe d in the Figure 3-6b. It is formed by eight octahedra; two central octahedrons share a face formed by O1/O6/O7, and these are linked to six outer octahedra by the e dges along O16/O1, O20/O6 and O7/O24. Fe7 Fe2 Fe4 Fe6 Fe8 Fe3 Fe5 Fe1 N1 N2 N3 O2 O6 O20 O9 O24 O7 O8 O16 O1 O3 O13 O10 O18 O19 O17 O4 O5 O21 O23 O22 O15 O14 O26 O27 O25 O11 O12 Fe7 Fe2 Fe4 Fe6 Fe8 Fe3 Fe5 Fe1 N1 N2 N3 O2 O6 O20 O9 O24 O7 O8 O16 O1 O3 O13 O10 O18 O19 O17 O4 O5 O21 O23 O22 O15 O14 O26 O27 O25 O11 O12a) b) Fe7 Fe2 Fe4 Fe6 Fe8 Fe3 Fe5 Fe1 N1 N2 N3 O2 O6 O20 O9 O24 O7 O8 O16 O1 O3 O13 O10 O18 O19 O17 O4 O5 O21 O23 O22 O15 O14 O26 O27 O25 O11 O12 Fe7 Fe2 Fe4 Fe6 Fe8 Fe3 Fe5 Fe1 N1 N2 N3 O2 O6 O20 O9 O24 O7 O8 O16 O1 O3 O13 O10 O18 O19 O17 O4 O5 O21 O23 O22 O15 O14 O26 O27 O25 O11 O12 Fe7 Fe2 Fe4 Fe6 Fe8 Fe3 Fe5 Fe1 N1 N2 N3 O2 O6 O20 O9 O24 O7 O8 O16 O1 O3 O13 O10 O18 O19 O17 O4 O5 O21 O23 O22 O15 O14 O26 O27 O25 O11 O12 Fe7 Fe2 Fe4 Fe6 Fe8 Fe3 Fe5 Fe1 N1 N2 N3 O2 O6 O20 O9 O24 O7 O8 O16 O1 O3 O13 O10 O18 O19 O17 O4 O5 O21 O23 O22 O15 O14 O26 O27 O25 O11 O12a) b) Figure 3-6. a) ORTEP represen tation in PovRay format of the side unit of complex 6; b) representation of the side unit by octa hedra. Fe yellow; O red; N blue. Hydrogen atoms have been omitted for clarity

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70 Charge balance considerations require the ir on ions to be in the oxidation state of +3, and three O atoms to be protonated. A bond valence sum (BVS) calculation allowed to identify O32, O34 and O28 as th e O atoms protonated (BVS: O32=1.2109; O34=1.149; O28= 0.992). Complex 6 is soluble in many organic solvents and was subjected to a variety of r eactivity studies. These included reactions with organic bases (pyridine, bipyridine) to see if deprotonation of the bridging hydroxide ions might trigger a nuclearity change, but in t hose cases where we were able to isolate a clean product, spectroscopic evaluation revealed that they we re already known or the starting material. Similarly, many changes to the reaction reag ent ratios and solvent (from EtOH to MeOH) were made to divert the reaction to a different product, but again complex 6 and already known products as the ferric wheel94 were the only products identified. 3.3.3 Magnetochemistry of Complexes 4, 5 and 6 3.3.3.1 Direct current magnetic st udies of complexes 4 6 Variable-temperature dc magnetic susceptibility ( M) data were collected in the 5 to 300 K range in a 1 kG (0.1 Tesla) magnetic fi eld. Microcrystalline samples of complexes 46 were restrained in eicosane to prevent tor quing, and a diamagnetic correction of the magnetic susceptibility ( M) was applied using Pascal's constants.95 In the dc magnetic susceptibility data recorded for compound 4, the MT decreases steadily from 36.77 cm3 mol-1K at 300 K to 24.26 cm3 mol-1 K at 5.00 K (Figure 3-7), indicating antiferromagnetic interactions w ithin the molecule but a significant ground state spin S , nevertheless.

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71 Temperature (K) 050100150200250300 M T (cm 3 mol -1 K) 22 24 26 28 30 32 34 36 38 Figure 3-7. Plot of MT vs. temperature for a dried, microcrystalline sample of complex 4 in eicosane, measured in a 1.0 kG field The ground state spin was determined by tw o methods; fitting of dc magnetization vs. field ( H ) and temperature ( T ) data. The ground-state spin value was determined by fits of dc magnetization ( M ) data collected in the 1.8 K and 0.1 T ranges. For a system occupying only the ground state and experi encing no zero-field splitting (ZFS), the various isofield lines wo uld be superimposed and M / N B would saturate at a value of g S . The data were fit using MAGNET,54 which assumes only the ground state is populated at these temperatures and is based on th e method described elsewhere involving diagonalization of the spin Hamiltonian matrix, including axial ZFS (2S Dz) and Zeeman interactions, and incorpor ating a full powder average.96 When data collected at fields higher than 0.5 T were used, the quality of the fits was poor, suggesting that excited states with S greater than the ground state are stabilized by the applied field and become populated even at these low temperatures. Th e data are plotted as reduced magnetization ( M / N B) vs. H / T , where N is Avogadro’s number and B is the Bohr magneton. The best fit is shown as solid lines in Figure 3-8 for complex 4, and two good fits were obtained,

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72 depending on the sign of D: S = 6, g = 2.23, D = -0.0047 cm-1, and S = 6, g = 2.26, D = 0.0045 cm-1. H/T (KG/ K) 0.00.51.01.52.02.53.0 M/N B 0 2 4 6 8 10 0.1 T 0.2 T 0.3 T 0.4 T fitting Figure 3-8. Determination of ground stat e spin. Plot of reduced magnetization M / N B vs. H / T for a dried, microcrystalline sample of complex 4 in eicosane; the dc field value of each of the isofie ld plots is indicated In order to assess the sign of D, to confirm that the obtained parameters were the true global rather than local minimum, a nd to assess the uncert ainty in the obtained g and D values, a root-mean square D vs. g error surface for the fit was generated using the program GRID.97 g 2.202.222.242.262.282.30 D (cm-1) -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 0.1 0.2 0.3 0.4 2.20 2.22 2.24 2.26 2.28 2.30-0. 0 -0.004 -0.002 0.000 0.002 0.004 0.006errorgD ( cm1) a)b) g 2.202.222.242.262.282.30 D (cm-1) -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 0.1 0.2 0.3 0.4 2.20 2.22 2.24 2.26 2.28 2.30-0. 0 -0.004 -0.002 0.000 0.002 0.004 0.006errorgD ( cm1) a)b) Figure 3-9. Two-dimensional contour plot of the error surface for the D vs. g fit for complex 4 (a), the asterisk indicates the soft minimum, and (b) threedimensional mesh plot error vs. g vs. D for the same fit for complex 4

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73 The error surface for 4 is shown in Figure 3-9a as a contour plot for the D = -0.007 to 0.007 cm-1 and g = 2.20 to 2.30 ranges, and as a mesh plot of the error vs. D vs. g in Figure 3-9b. These plots of the fit show that the fit with pos itive D is superior, suggesting this to be the true sign of D. Dc magnetic susceptibi lity data for compound 5 are shown in Figure 3-10a as MT vs. T . The inset shows the temperature depende nce of the effective magnetic moment (eff vs. T ). This monomeric complex follows the Curie-Weiss behavior for a S = 1 complex corresponding to a Ni(II) ion with two unpaired electrons. The room temperature value of the effective magnetic moment, eff/B = 3.04 is as expected fr om the spin-only formula eff = g S ( S +1), Ni(II) possessing two unpaired elect rons. The best fit using the Curie equation: M = 2 N g2 B 2 / 3 k ( T ) for an S = 1 species, is show n in Figure 3-10b as a solid line, and the fit parameters were g = 2.20(1) and a Curie-Weiss constant of = -2.7 (3) K. The negative Curie-Weiss constant indicates weak antiferromagnetic exchange interactions. T (K) 050100150200250300350 1/ M (mol/cm3) 0 50 100 150 200 250 300 experimental fitting 020406080100 0 20 40 60 80 100 T (K) 050100150200250300 MT (cm3 mol-1 K) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 050100150200250300 eff / B 2.0 2.5 3.0 a) b) T (K) 050100150200250300350 1/ M (mol/cm3) 0 50 100 150 200 250 300 experimental fitting 020406080100 0 20 40 60 80 100 T (K) 050100150200250300 MT (cm3 mol-1 K) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 050100150200250300 eff / B 2.0 2.5 3.0 a) b) Figure 3-10. a) Plot of MT vs. T for complex 5. eff vs. T as inset plot. b) Plot of 1/ M vs. T for 5. Inset: the solid line represents a fit to the Curie–Weiss law

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74 T (K) 050100150200250300 M T (cm 3 mol -1 K) 0 10 20 30 40 Figure 3-11. Plot of MT vs. temperature for a dried, microcrystalline sample of complex 6 in eicosane, measured in a 1.0 kG field The MT for 6 decreases steadily with decrea sing temperature from 33.33 cm3 mol-1 K at 300 K to 0.97 cm3 mol-1 K at 5.00 K (Figure 3-11). The value of MT for this complex at 300 K of 33.33 cm3 mol-1 K is below the spin only value of 96.25 cm3 mol-1 K expected for a complex consisting of tw enty-two non interacting Fe(III) ions. The lowest temperature data suggest an S = 0 spin ground state, cons istent with the expected antiferromagnetic coupling between Fe(III) ions. 3.3.3.2 Alternating current magnet ic susceptibility studies In order to independently confirm the ground state of complex 4, the influence of the applied dc field was removed comp letely by carrying out ac susceptibility measurements in the 1.8 K range with a 3.5 G ac field oscillating at frequencies in the 50 Hz range. The in-phase ( M ) signal (Figure 3-12) is te mperature-independent in this temperature range at ~25 cm3 mol-1 K, giving S = 6 and g 2.2, in satisfying agreement with the dc fit parameters.

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75 Temperature (K) 024681012 M'T (cm3 mol-1 K) 0 5 10 15 20 25 30 250 Hz 498 Hz 998 Hz Figure 3-12. Plot of the in-phase (as M T ) ac susceptibility signals vs. temperature for dried, microcrystalline samples of complex 4 in eicosane at the indicated oscillating frequencies In general, the in-phase ac susceptibility ( M) is invaluable for the determination of the ground-state spin of a molecule. The M T vs. T plots of 4 are temperatureindependent. The value of M T in the temperature-independent region is especially useful to estimate the ground-state spin without the interference of even a small dc field 3.4 Conclusions The use of mdaH2 has led to two particularly hi gh nuclearity Fe and Ni clusters, which suggests that even larger molecular polynuclear clusters of these and other paramagnetic 3d metals may be possible. The flexibility of mdaH2 as a chelating ligand in Fe and Ni chemistry has allowe d access to a stru cturally novel Fe22 compound, emphasizing the effectiveness of the oxo/ hydroxo/alkoxo functionality in promoting high-nuclearity product formation, and in the case of Ni24 making the molecule attractive for its aesthetic appeal. Complexes 4 and 6 represent the largest and sec ond largest homometallic clusters with Fe and Ni, respectively. This demonstrates the immens e potential of alkoxide-based

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76 ligands in cluster syntheses. T hus, the use of such ligands is a continuing research effort in our group and has resulted in many new cl usters being synthesized and characterized, some of which will be reported in the next chapter.

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77 CHAPTER 4 A NOVEL FAMILY OF Fe7 COMPLEXES WITH S = 5/2 4.1. Introduction As a part of the ongoing inve stigation of the chemistry of metal complexes with alkoxide-based ligands, the reactivity of N-methyldiethanolamine (mdaH2) has been explored with different iron star ting materials. Hydrolysis of iron salts in the presence of carboxylate groups, with or wit hout other chelating ligands, has proven to be a very useful method for obtaining both oxideand hydroxide-containing clusters. This approach has resulted in a number of compounds with diverse nuclearities and Fex topological arrangements. An example of a pr oduct obtained with th e tridentate ligand Nmethyldiethanolamine (mdaH2) with Fe(III) is the Fe22 complex.105 In an effort to further study this reaction system, studies we re conducted to obtain analogs of 6; in this case, the reaction was performed with sodium benzoate instead of sodium acetate, to investigate the carboxylate dependence. Particularly attr active has been the family of trinuclear complexes of formula [Fe3O(O2CR)6X3]n+, where X = H2O, py, etc., and n = 0, 1.98 These "triangular" complexes have been widely used as iron starting materials, and the work presented uses a combination of both the afor ementioned approaches, as a route to novel higher nuclearity complexes. The importance of high-nuclearity iron com pounds in the magnetism area is due to the fact that each high spin iron (III) ion has a large num ber of unpaired electrons ( S =5/2) and undergoes strong magnetic exchange in teractions within iron-oxo clusters. Consequently, these compounds have the poten tial of displaying overall high spin ground

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78 states and acting as building blocks for mol ecular-based magnetic materials or even as single molecule magnets (SMMs).5, 17a, 99 However, the interactions between FeIII are normally antiferromagnetic and compounds with S = 0 or S = ground states cannot function as single-molecule magnets. Neverthe less, when spin frustration occurs, where there are at least three center s antiferromagnetically coupled within a tr iangular unit, then there are competing exchange interactions th at can yield intermediate or even parallel spin alignment between spin cen ters that are antiferromagneti cally coupled, i.e., the latter interaction is frustrated. In these cases, a nd depending on the distri bution of frustrated pathways, the complex can possess an S 0 ground state. Single-molecule magnets are molecule s possessing a large barrier (vs. k T ) to magnetization relaxation, and thus display magnetization vs. applied field hysteresis loops at low enough temperatures, th e diagnostic property of a magnet.19, 20 SMMs derive their properties from a combinati on of large ground state spin ( S ) value and a significant magnetoanisotropy of the Ising (easy-axis) t ype (negative zero-fiel d splitting term, D). Iron SMMs are of great in terest, because it is known100 that the nuclear spin of the transition metal in a polynuclear SMM aff ects the rate of quantum tunneling of magnetization (QTM) (Mn has a nuclear spin of I = 5/2 and ~ 100% natural abundance, whereas 56Fe has I = 0 and ~97-8% natural abundance), and these QTM effects have led to the idea that SMMs could be exploited as qubits in quantum computing.8 In addition, SMMs that have half-integer spin ground states are predicted101 to have QTM suppressed in the absence of a magnetic field. However, several half-integer spin polynuclear Mn SMMs have been studied102,14 and in spite of the above prediction, QTM was observed. It has been concluded that the nuc lear spin of such a polynuclear Mn SMM leads to a small

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79 magnetic field, the transverse component of which leads to QTM. As a consequence of the above observations, an important goal in th e area of SMMs is to prepare a half-integer spin SMM consisting of metal ions with no nuclear spin (such as 56Fe). Additionally, it is important to understand the magnitude and natu re of the magnetic couplings (exchange interactions) in polynuclear me tal complexes, as these govern the SMM behavior and the quantum tunneling effects displayed by such co mplexes. In this ch apter, a family of isostructural and related Fe7 complexes will be presented, all of which possess an S = 5/2. Additionally, one of these has been shown to behave as a single-molecule magnet. In order to rationalize the observed magnetic prope rties as a function of the core topologies and the presence of spin frustration effects, ZILSH calculations will also be presented for these complexes. 4.2 Experimental 4.2.1 Syntheses All manipulations were performed under aerobic conditions us ing materials as received, except where otherwise noted. Abbreviations: mdaH2 = Nmethyldiethanolamine. The complexes [Fe3O(O2CPh)6(H2O)3](NO3) and [Fe3O(O2CtBu)6(H2O)3](NO3) were prepared according to the literature methods.103 [Fe7NaO3(O2CPh)9(mda)3](ClO4) (7). To a stirred solution of FeCl3H2O (1.0 g, 3.7 mmol) in H2O (20 mL), Na(O2CPh) (1.5 g, 10.5 mmol) was added, and a precipitate appeared. This precipitate was coll ected by filtration, washed with H2O, air-dried, and the resulting dry solid dissolved in MeCN. To this solution, mdaH2 was added (0.2 mL, 1.0 mmol) and stirred for 20 min. Addition of NaClO4 (0.2 g, 1.6 mmol), and layering of this solution with ether gave red-orange crystals of 73Et2O. These crystals were suitable for X-ray crystallography. The yield was ~32 %. Elemental analysis for

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80 [Fe7NaO3(O2CPh)9(mda)3]ClO4H2O (C78H82N3Fe7O33ClNa): Experimental (calculated): C, 45.95; H, 4.05; N, 2.06. Found: C, 45.68; H, 3.80; N, 1.93 %. Selected FT-IR data (KBr, cm-1): 1601 (s), 1560 (s), 1493 (m), 1408 (s), 1176 (m), 1070 (m), 1025 (m), 938 (w), 840 (w), 813 (w), 717 (s), 686 (w), 674 (w), 627 (w), 480 (m). [Fe7O3(O2CPh)9(mda)3(H2O)] (8). mdaH2 (0.2 mL, 1.0 mmol) was added to a stirred orange solution of [Fe3O(O2CPh)6(H2O)3]NO3 (0.5 g, 0.45 mmol) in MeCN (25 mL). The resulting orange solution was layere d with ether. After several days, light brown crystals of 8 were collected by filtration, washed with ether (2 x 10mL), and dried in air. These crystals were obtained in 36% isolated yield. Elemental analysis for [Fe7O3(O2CPh)9(mda)3(H2O)] (C78H80N3Fe7O28): Experimental (calculated): C, 49.35; H, 4.25; N, 2.21. Found: C, 49.52; H, 4.14; N, 2.15 %. Selected FT-IR data (KBr, cm-1): 1599 (s), 1558 (s), 1519 (m), 1497 (m), 1447 (s), 1398 (s), 1174 (m), 1103 (m), 1061 (m), 1025 (m), 999 (m), 865 (m), 837 (w), 758 (w), 716 (s), 686 (s), 673 (s), 617 (m), 580 (m), 530 (m), 466 (m). [Fe7O3(O2CtBu)9(mda)3(H2O)3] (9). To a stirred orange solution of [Fe3O(O2CtBu)6(H2O)3]NO3 (0.5 g, 0.56 mmol) in MeCN (25 mL) was added mdaH2 (0.20 mL, 1.0 mmol). The resulting orange so lution was stirred for an additional 30 min. and then layered with ether. After se veral days, light brown crystals of 9 were collected by filtration, washed with ether (2 x 15mL), and dried in air. Crystals of the complex were obtained in 43% isolated yield. Elemental analysis for [Fe7O3(O2CtBu)9(mda)3(H2O)] (C60H120N3Fe7O30): Experimental (calculated): C, 41.07; H, 6.89; N, 2.39. Found: C, 40.95; H, 6.94; N, 2.45 %. Selected FT-IR data (KBr, cm-1): 1575 (s), 1536 (w), 1483 (s), 1424 (s), 1363 (m), 1228 (m), 1098 (m), 1058 (m), 1029

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81 (m), 1000 (m), 904 (w), 880 (w), 679 (m), 602 (m), 581 (m), 528 (m), 484 (w), 438 (w), 419 (w), 406 (w). 4.2.2 X-Ray Crystallography Suitable crystals were selected from the bulk samples, maintained in mother liquor to avoid solvent loss, attached to the tip of a glass capillary an d transferred to the goniostat, where they were cooled to 173 K fo r characterization and data collection. Data on complexes 7Et2O, 8 and 9 were collected on a Siemens SMART PLATFORM equipped with a CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were re fined using up to 8192 reflections. A full sphere of data (1850 fram es) was collected using the -scan method (0.3 frame width). The first 50 frames we re re-measured at the end of data collection to monitor instrument and crystal stability (maxim um correction on I was < 1 %). Absorption corrections by integration were applied ba sed on measured indexed crystal faces. The structures were solved by Direct Methods in SHELXTL6 ,31 and refined on F2 using fullmatrix least squares. The non-H atoms we re treated anisotropically, whereas the hydrogen atoms were calculated in ideal pos itions and were riding on their respective carbon atoms. The solvent molecules could not be modeled properly, and thus program SQUEEZE32, a part of the PLATON33 package of crystallographic software, was used to calculate the solvent disorder area and rem ove its contribution to the overall intensity data. Complex 7Et2O crystallizes in the space group P 21/ c . The asymmetric unit consists of the Fe cluster, a perchlorate ani on and three ether molecule s of crystallization.

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82 A total of 1090 parameters were refined in the final cycle of refinement using 15057 reflections with I > 2(I) to yield R1 and w R2 of 4.87% and 12.83%, respectively. Table 4-1. Crystallographic data for complexes 7Et2O, 8 and 9 Parameter 7 8 9 formulaa C86 H98 N3 Fe7 Cl Na O33 C78 H80 N3 Fe7 O28 C60 H120 Fe7 N3 O30 fw, g mol-1 2151.11 1898.44 1754.56 space group P 21/ c 3 a P R 3 a , 14.4336(9) 24.9810(5) 26.5134(8) b , 19.3937(11) 24.9810(5) 26.5134(8) c , 36.307(2) 24.9810(5) 10.5013(6) , deg 90 90 90 , deg 91.9760(10) 90 90 , deg 90 90 120 V , 3 10157.2(11) 15589.4(5) 6393.0(5) Z 19 8 3 T , K 173(2) 173(2) 173(2) radiation, b 0.71073 0.71073 0.71073 calc, g cm-3 1.482 1.618 1.362 R 1 ( wR 2), %c , d 4.87 (12.83) 4.63 (11.66) 3.87 (7.94) a Including solvent molecules. b Graphite monochromator. c R 1 = || Fo| – | Fc|| / | Fo|. d wR 2 = [w ( Fo 2 Fc 2)2] / [ w Fo 2)2]]1/2 where S = [[ w ( Fo 2 – Fc 2)2] / ( n p )]1/2, w = 1/[2( Fo 2) + ( m * p )2 + n * p ], p = [max( Fo 2, 0) + 2* Fc 2]/3, and m and n are constants Complex 8 crystallizes in the cubic space group 3 a P . The asymmetric unit consists of a 1/3 Fe7 cluster. There are two major disord ers: the C13 phenyl ring displays a rotational disorder where both rings have at om C14 in common. The second disorder involves the C21 (and consequently phenyl C21’) benzoate lig and being bidentate chelating in one instance, a nd in the other instance is m onodentate and there is a water molecule occupying the second site. The occupa tion factors of all atoms of the disorders were dependently refined. In order to ascerta in that this disorder is not introduced by choosing the higher symmetry space group 3 a P, the structure was refined in the noncentrosymmetric space group as well as or thorhombic space group Pbca. In both cases the disorders were observed, thus proving that 3 a P is the correct space group in which

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83 the structure was refined. A total of 366 parameters were refined in the final cycle of refinement using 5590 reflections with I > 2(I) to yield R1 and w R2 of 4.63% and 11.66%, respectively. Complex 9, which crystallizes in the sp ace group R3, used a total of 302 parameters in the final cycle of refi nement, using 6257 reflections with I > 2(I) to yield R1 and w R2 of 3.87% and 7.94%, respectively. Cr ystallographic unit cel ls and structure solution data are listed in Table 4-1. 4.2.3 Single-Crystal, High-Frequency EPR Spectroscopy High field electron paramagnetic resona nce (HF-EPR) measurements were performed using a variable-frequency, cavity-b ased, high sensitivity spectrometer in Dr. Stephen Hill’s lab at the University of Florid a. They were conducted on a single crystal at various frequencies from 50 to 200 GHz and angles from the c-axis to ab-plane. A sensitive cavity-perturbation t echnique and a Millimeter-wave Vector Network Analyzer (MVNA) were used to detect the EPR signa ls from the single crystal (details are described elsewhere)104. The spectra were obtained at fixed microwave frequencies and temperatures while sweeping the dc magnetic fields. The crystal was removed from the mother liquor and immediately protected with grease to prevent potential solvent loss. The crystal was then cooled in helium gas to low temperatures. 4.3 Results and Discussion 4.3.1 Syntheses As an extension of the work describe d in Chapter 3, where the use of mdaH2 and carboxylate ligands promoted the formation of high nuclearity complexes, reactions involving different ir on salts than FeCl3 with mdaH2 and other carboxylates have been explored herein. Additionally, the reaction of preformed lower nuclearity complexes with

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84 chelating ligands has been proven a successful strategy and many synthetic procedures to Fex clusters rely on th e reaction of [Fe3O(O2CR)6L3]+ complexes with chelating ligands. For those reason different reactions were performed, where 1 equivalent of mdaH2 was added to a reaction mixture of FeCl3, NaO2CPh and NaClO4 in MeCN. Also, three equivalents of mdaH2 were added to [Fe3O(O2CBut)6(H2O)3](NO3) and [Fe3O(O2CPh)6(H2O)3](NO3) in MeCN, and all these thr ee reaction systems successfully produced higher nuclearity pr oducts, heptanuclear [Fe7O3]15+ products. These three reactions are summarized in Eqs. 4-1, 4-2 and 4-3, respectively. 7 FeCl3 + 9 Na(O2CPh) + 3 mdaH2 + NaClO4 [Fe7NaO3(O2CPh)9(mda)3]ClO4 + 9 NaCl + 12 Cl+ 6 H+ (4-1) 3 [Fe3O(O2CPh)6(H2O)3]NO3 + 3 mdaH2 [Fe7O3(O2CPh)9(mda)3(H2O)] + 2 Fe3+ + 3 NO3 + 3 PhCO2 + 6 PhCO2H + 8 H2O (4-2) 3 [Fe3O(O2CBut)6(H2O)3]NO3 + 3 mdaH2 [Fe7O3(O2CBut)9(mda)3(H2O)3] + 2 Fe3+ + 3 NO3 + 3 tBuCO2 + 6 tBuCO2H+ 6 H2O (4-3) There are some features that make these unprecedented oxo-iron complexes remarkable. These complexes are in the rela tively small family of polynuclear oxo-iron complexes with an odd number of metal ions. Different ratios for Eq. 4-1 were tried but complex 7 was the only compound crystallized. Differe nt solvents were also used (i.e., CH2Cl2, and EtOH). The initial precipitate of FeCl3, NaO2CPh was insoluble in CH2Cl2. While, the initial precipitate dissolve using EtOH, but it was not po ssible to obtain any crystal.

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85 Other examples of such compounds with equa l nuclearity and rela ted structure are: [Fe7(C4H9NO2)6Cl6]2MeCNH2O62a, where C4H9NO2 = 2-amino-2-methyl-1,3propanediol and [FeIIIFeII 6(MeO)6(HL)6]Cl3 62b where H2L = 3-methoxy-2 salicylideneamino-1-ethanol. Another rare attr ibute of these hepta nuclear complexes is the non planar core of the structures , compared to the two already known Fe7 complexes mentioned earlier. 4.3.2 Description of Structures 4.3.2.1 Structure of [Fe7NaO3(O2CPh)9(mda)3](ClO4) (7) An ORTEP represen tation of complex 7 is shown in Figure 4-1, and bond distances and angles are listed in Tabl e A-7. Crystallographic data are listed in Table 4-1. Fe1 Na Fe4 Fe2 Fe3 Fe7 Fe6 Fe5 O5 O10 O17 O6 O4 O18 O16 O15 O14 O9 O21 O22 a) b) Fe1 Na Fe4 Fe2 Fe3 Fe7 Fe6 Fe5 O5 O10 O17 O6 O4 O18 O16 O15 O14 O9 O21 O22 a) b) Figure 4-1. ORTEP representations in PovRay format of (a) complex 7, where only the ipso carbon atoms of the benzoate group are shown, and (b) the core of complex 7 . Fe yellow; O red; N blue; Na blue; C gray. For clarity, hydrogen atoms have been omitted The core of the structure is composed of seven iron ions. The structure consists of a central octahedral iron i on (Fe4) linked by three 4-oxos (O5, O10, O17), three 2-oxide (O4, O14, O22) and three 2-alkoxide (O9, O16, O18) to th e outer six iron ions. It can therefore be regarded as a wheel with C3 symmetry. Each pair of the Fe on the rim (Fe1/ Fe2, Fe3/Fe7, Fe6/Fe5) are linked through three 2-alkoxide from the mda2ligand. Each

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86 pair (Fe2/Fe3, Fe7/Fe6, Fe5/Fe1) is additi onally bridged by an acetate group in a rare 1, 2, ( syn , syn , anti ) binding mode, where the oxygen is connected to the iron ion (Fe1, Fe3, Fe6) and to the sodium ion. The iron and oxygen oxidation st ate assignments were established by consideration of bond distances and bond-valence sum (BVS) calculations.46, 47 All Fe centers are six-coordinate a nd possess near-octahedral geometry. Table 4-2. Bond valence sum calculationsa for complex 7Et2O Atom Fe2+ Fe3+ Fe(1) 2.812 3.057 Fe(2) 2.809 3.068 Fe(3) 2.809 3.054 Fe(4) 2.907 3.161 Fe(5) 2.811 3.070 Fe(6) 2.811 3.057 Fe(7) 2.786 3.043 a The underlined value is the one closest to the actual charge for which it was calculated. The oxidation state of a particular atom can be taken as the nearest whole number to the underlined value 4.3.2.2 Structure of [Fe7O3(O2CPh)9(mda)3(H2O)] (8) An ORTEP represen tation of complex 8 is shown in Figure 4-2, and bond distances and angles are listed in Table A-8. Crystallographic data are listed in Table 4-1. The core of the structure is composed of seven iron ions which are related by C3 crystallographic symmetry. The structure consists of a central octahedral iron ion (Fe2) linked by three 3oxides (O7 and symmetry related) and three 2-alkoxides (O2 and symmetry related) to the outer six iron ions (Fe1, Fe 3 and symmetry related). Each pair of Fe on the rim (Fe1/ Fe3) is linked through three 2-alkoxides (O1) from the mda2chelates. Each pair (Fe3/Fe1A) is additionally bridged by an acetate group in the familiar 1, 1, ( syn , syn ) binding mode.

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87 Fe2 Fe3 Fe1A Fe1 Fe3A Fe3B Fe1B O7 O2 O8 O10 C21 O1 b) a) Fe2 Fe3 Fe1A Fe1 Fe3A Fe3B Fe1B O7 O2 O8 O10 C21 O1 b) a) Figure 4-2. ORTEP representations in PovRay format of (a) complex 8, where only the ipso carbon atoms of the benzoates groups are shown, and (b) the core of complex 8 showing the benzoates groups that have disorder and the hydrogen bonds (dotted lines). Fe yellow; O red; N blue; C gray. For clarity, hydrogen atoms have been omitted In the structure, three of the benzoate groups have a disorder which involves the benzoate ligand being bidentate in one inst ance, and in the other instance monodentate along with a water molecule occupying the s econd site. This disorder results in a hydrogen-bond with the H2O molecule involved (O8O10 = 2.540 ). The iron and oxygen oxidation state were established by consideration of bond distances and bondvalence sum (BVS) calculations.46, 47 Table 4-3. Bond valence sum calculationsa for complex 8 Atom Fe2+ Fe3+ Fe(1) 2.972 3.231 Fe(2) 2.823 3.083 Fe(3) 2.895 3.148 a The underlined value is the one closest to the actual charge for which it was calculated. The oxidation state of a particular atom can be taken as the nearest whole number to the underlined value

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88 4.3.2.3 Structure of [Fe7O3(O2CtBu)9(mda)3(H2O)3] (9) An ORTEP representation of 9 is displayed in Figur e 4-3 and selected bond distances and angles are listed in Table A-9. Cr ystallographic data are listed in Table 4-1. The core as described previously is composed of seven iron ions, and has C3 symmetry. O2 Fe3 Fe2 O1 Fe1 O3 a) b) Fe2 Fe3 Fe2 Fe3 O2 Fe3 Fe2 O1 Fe1 O3 a) b) Fe2 Fe3 Fe2 Fe3 Figure 4-3. ORTEP representa tions in PovRay format of (a) complex 9 showing the hydrogen bonds. Only the ipso carbon atom s of the pivalate groups are shown, and (b) the core of complex 9. Fe yell ow; O red; N blue; C gray. For clarity, hydrogen atoms have been omitted The central iron ion (Fe1) is linked to the iron ions in the periphery by three 3-O2ions (O2) and three 2-OR (O1) from the chelating mda2ligands. In this structure, the three pivalates are terminal and they from a hydrogen bond with the th ree water molecules (O8O9 = 2.565 ). The iron and oxygen oxida tion state assignments were established by consideration of bond distances an d bond-valence sum (BVS) calculations.46, 47 The rest of the structure is same as complex 8, as already described earlier. Table 4-4. Bond valence sum calculationsa for complex 9 Atom Fe2+ Fe3+ Fe(1) 2.895 3.148 Fe(2) 2.835 3.096 Fe(3) 2.887 3.139 a The underlined value is the one closest to the actual charge for which it was calculated. The oxidation state of a particular atom can be taken as the nearest whole number to the underlined value

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89 4.3.3 Magnetochemistry of Complexes 7, 8 and 9 4.3.3.1 Direct current magnetic st udies of complexes 7 9 Variable-temperature magnetic susceptib ility measurements were performed on powdered polycrystalline samples of complexes 7-9, restrained in eicosane to prevent torquing, in a 10 kG field and in the 5.0-300 K range. The data are shown as MT vs . T plots. All complexes exhibit simila r behavior. The value of MT for complex 7 decreases from 10.18 cm3 mol-1 K (9.02 B) at 300 K to 4.25 cm-3 mol-1 K (5.83 B) at 5.0 K. For complex 8, MT decreases from 8.15 cm3 mol-1 K (8.07 B) at 300 K to 3.97 cm3 mol-1 K (5.63 B) at 5.0 K. Complex 9 exhibits similar behavior, with MT decreasing from 9.00 cm-3 mol-1 K (8.48 B) at 300 K to 4.43 cm-3 mol-1 K (5.95 B) at 5.0 K. These data are plotted as MT vs. T in Figure 4-4. The insets figures are the plots of eff vs. T . Temperature (K) 050100150200250300 M T (cm3 mol-1 K) 1 2 3 4 5 6 7 8 9 10 Complex 7 Complex 8 Complex 9 050100150200250300 eff ( B ) 5 6 7 8 9 Figure 4-4. Plot of MT vs. T for complexes 7, 8 and 9. The inset is a eff vs. T plot The MT value at room temperature for these complexes is considerably below the spin-only value expected for se ven non-interacting high spin FeIII ions (30.62 cm3 mol-1

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90 K, 15.65 B), revealing the presence of strong an tiferromagnetic interactions in the complexes. The decrease in MT is due to the thermal populat ion of excited states with S < 5/2. To confirm the ST = 5/2 ground state spin anticipated from the MT value at 5.0 K, and to determine the magnitude of the zero-field splitting parameter D , magnetization vs . dc field measurements were made for restrained samples of 7-9 at applied magnetic fields and temperatures in the 10 70 kG a nd 1.8-10.0 K ranges, respectively. H/T (KG/H) 01020304050 M/N B 0 1 2 3 4 5 0.1 T 0.5 T 1T 2 T 3 T 4 T 5 T 6 T 7 T fitting H/T (KG/H) 010203040 M/N B 0 1 2 3 4 5 0.1 T 0.5 T 1.0 T 2.0 T 3.0 T 4.0 T 5.0 T 6.0 T 7.0 T fitting H/T (KG/K) 010203040 M/N B 0 1 2 3 4 5 0.1 T 0.5 T 1.0 T 2.0 T 3.0 T 4.0 T 5.0 T 6.0 T 7.0 T fitting a)b) c) H/T (KG/H) 01020304050 M/N B 0 1 2 3 4 5 0.1 T 0.5 T 1T 2 T 3 T 4 T 5 T 6 T 7 T fitting H/T (KG/H) 010203040 M/N B 0 1 2 3 4 5 0.1 T 0.5 T 1.0 T 2.0 T 3.0 T 4.0 T 5.0 T 6.0 T 7.0 T fitting H/T (KG/K) 010203040 M/N B 0 1 2 3 4 5 0.1 T 0.5 T 1.0 T 2.0 T 3.0 T 4.0 T 5.0 T 6.0 T 7.0 T fitting a)b) c) Figure 4-5. Plot of M / N B vs. H / T for dried samples of (a) complex 7 (b) complex 8, and (c) complex 9 in eicosane at the indicated applied fields. The solid lines are the fit of the data; see the text for the fitting parameters The data for complexes 7 9 are shown as reduced magnetization ( M / N B) vs . H / T plots, where M is the magnetization, N is Avogadro’s number, B is the Bohr magneton,

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91 and H is the magnetic field. The program MAGNET54 was employed to fit the experimental data to those calculated using the above procedure for different values of S , D and g . The best fit for 7-9 is shown as the solid lines in Figure 4-5. Reasonable fits were obtained with two sets of paramete rs, in all cases assuming the spin was S = 5/2 for all compounds: g = 2.05, D = -0.49/0.58 cm-1 for 7; g = 1.94/1.95 with D = -0.42/0.55 cm-1 for 8 and g = 1.90, D = -0.43/0.58 cm-1 for 9. In case of complex 7 there is a possibility of g = 2.00 and D = 0, but this case is not considered because of the bad fitting of the M / N B vs. H / T . To determine whether the values found for D are positive or negative we generated the gl obal fitting minimum using root-mean-square error as a function of g and D. For complexes 7 -9, these error surfaces are shown in Figure 4-6 to 4-8 as a 2-D contour and as 3-D mesh plots. For complex 7 (Figure 4-6) and for complex 8 (Figure 4-7) the positive fit was superior. While for complex 9 (Figure 4-8), equally good fits are observed for both positive and negative D values. g 1.901.952.002.052.10 D (cm-1) -1.0 -0.5 0.0 0.5 1.0 0.0 0.2 0.4 0.6 0.8 1.0 1.8 1.9 2.0 2.1 2.2 2.3 2.4 -1.5 -1.0 -0.5 0.0 0.5 1.0e r r o rgD ( c m1 ) a)b) g 1.901.952.002.052.10 D (cm-1) -1.0 -0.5 0.0 0.5 1.0 0.0 0.2 0.4 0.6 0.8 1.0 1.8 1.9 2.0 2.1 2.2 2.3 2.4 -1.5 -1.0 -0.5 0.0 0.5 1.0e r r o rgD ( c m1 ) a)b) Figure 4-6. Two-dimensional contour plot of the error surface for the D vs. g fit for complex 7 (a), the asterisk indicates the soft minimum, and (b) threedimensional mesh plot error vs. g vs. D for the same fit of complex 7

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92 g 1.901.911.921.931.941.951.961.971.98 D (cm-1) -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 0.00 0.05 0.10 0.15 0.20 0.25 0.30 1. 8 1.90 1.92 1.94 1.96 1.98 2.00 2.02 -0.5 0.0 0.5 1.0errorgD ( c m1) a) b) g 1.901.911.921.931.941.951.961.971.98 D (cm-1) -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 0.00 0.05 0.10 0.15 0.20 0.25 0.30 1. 8 1.90 1.92 1.94 1.96 1.98 2.00 2.02 -0.5 0.0 0.5 1.0errorgD ( c m1) a) b) Figure 4-7. Two-dimensional contour plot of the error surface for the D vs. g fit for complex 8 (a), the asterisk indicates the soft minimum, and (b) threedimensional mesh plot error vs. g vs. D for the same fit for complex 8 g 1.881.891.901.911.92 D (cm-1) -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 1.86 1.88 1.90 1.92 -0.4 -0.2 0.0 0.2 0.4 0.6errorgD ( c m1) a) b) g 1.881.891.901.911.92 D (cm-1) -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 1.86 1.88 1.90 1.92 -0.4 -0.2 0.0 0.2 0.4 0.6errorgD ( c m1) a) b) Figure 4-8. Two-dimensional contour plot of the error surface for the D vs. g fit for complex 9 (a), the asterisk indicates the soft minimum, and (b) threedimensional mesh plot error vs. g vs. D for the same fit for complex 9 4.3.3.2 Alternating current magnet ic susceptibility studies In order to confirm the obtained spin of the ground states of 7-9, ac studies were performed in the 1.8-10 K range using a 3.5 G ac field oscillating at frequencies in the 50 – 500 Hz range. If the magnetization vector can relax fast enough to keep up with the oscillating field, then there is no imagin ary (out-of-phase) susceptibility signal (M ), and the real (in-phase) susceptibility (M ) is equal to the dc susceptibility. For all the

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93 complexes 7 9, there is a plateau from 10 K to 1.8 K in the in-phase M' signal, when plotted as M' T , at a value in the 4 – 5 cm3 K mol-1 range. This is consistent with the expected MT = 4.38 cm-3 mol-1 K (5.91 B) of an S = 5/2 ground state and g = 2. In every case there was no out-of-phase M'' signal. The M 'T extrapolation values for complexes 7, 8 and 9 are ~ 4.3, ~ 4.4 and ~ 4.1 cm-3 mol-1 K, respectively. M 'T (cm 3 mol -1 K) 2 3 4 5 500 Hz 250 Hz 50 Hz M 'T (cm 3 mol -1 K) 2 3 4 5 500 Hz 250 Hz 50 Hz Temperature (K) 24681012 M 'T (cm 3 mol -1 K) 2 3 4 500 Hz 250 Hz 50 Hz M '' (cm 3 mol -1 ) 0.0 0.1 0.2 0.3 0.4 500 Hz 250 Hz 50 Hz M '' (cm 3 mol -1 ) 0.0 0.1 0.2 0.3 0.4 997 Hz 250 Hz 50 Hz Temperature (K) 24681012 M '' (cm 3 mol -1 ) 0.0 0.2 0.4 0.6 0.8 1.0 500 Hz 250 Hz 50 Hz a) b) M 'T (cm 3 mol -1 K) 2 3 4 5 500 Hz 250 Hz 50 Hz M 'T (cm 3 mol -1 K) 2 3 4 5 500 Hz 250 Hz 50 Hz Temperature (K) 24681012 M 'T (cm 3 mol -1 K) 2 3 4 500 Hz 250 Hz 50 Hz M '' (cm 3 mol -1 ) 0.0 0.1 0.2 0.3 0.4 500 Hz 250 Hz 50 Hz M '' (cm 3 mol -1 ) 0.0 0.1 0.2 0.3 0.4 997 Hz 250 Hz 50 Hz Temperature (K) 24681012 M '' (cm 3 mol -1 ) 0.0 0.2 0.4 0.6 0.8 1.0 500 Hz 250 Hz 50 Hz a) b) Figure 4-9. Plot of the in-phase (as M' T , a) and out-of-phase (as M'', b) ac susceptibility signals vs. temperature for dried, microcrystalline samples of complexes 7 (top), 8 (middle) and 9 (bottom) in eicosane at the indicated oscillation frequencies

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94 Since the M' T signal remains essentially constant in the temperature range observed, there is little cha nge in the distribution of popula tion of the states, which means that at the temperatures observed, only the ground state is populated. If there is a peak, the peak maxima clearly lie at temperatur es below 1.8 K, the operating limit of our instrument. Since the value of D was not clear from the root-mean-square error as a function of g and D. Studies at temperatures < 1. 8 K were necessary to investigate the single-molecule magnetism behavior for complex 9 (since it had a negative D value), and these were carried out on single crystals of this complex down to 0.04 K using a microSQUID instrument.55 The barrier to magnetization relaxation ( U ) whose upper limit is given by ( S2-)|D| for half-integer S values is 2.58 cm-1 (1.79 K) for complex 9 using the magnetization fit parameters with a negative value of D. In fact, the true or effective barrier ( Ueff) is usually significantly smaller than U due to QTM. 4.3.3.3 Magnetization vs. dc field hysteresis loops If a complex is a SMM below a certain temp erature, it will display hysteresis loops in magnetization vs. applied dc field plots. Shown in Figure 4-10 are the results of magnetization ( M ) vs. applied dc field scans of complex 9, at (i) 0.04 K and field sweep rates in the 0.28 0.0005 T/s range (left), and (ii) 0.002 T/s field sweep rate and temperatures in the 0.04 .25 K range (right). For complex 9, hysteresis loops were observed, establishing that this complex is a new single-molecule magnet. The coercivities of the hysteresis loops in Figure 4-10 increase with increasing sweep rates (Figure 4-10 a), and with decreasing temperatur es (Figure 4-10 b), as is expected for the superparamagnet like properties of SMMs.

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95 -1 -0.5 0 0.5 1 -0.4-0.3-0.2-0.100.10.20.30.4 0.280 T/s 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s 0.0005 T/s M/Ms 0H (T) 0.04 K -1 -0.5 0 0.5 1 -0.4-0.3-0.2-0.100.10.20.30.4 0.04 K 0.15 K 0.20 K 0.25 K M/Ms 0H (T) 0.002 T/sa) b) -1 -0.5 0 0.5 1 -0.4-0.3-0.2-0.100.10.20.30.4 0.280 T/s 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s 0.0005 T/s M/Ms 0H (T) 0.04 K -1 -0.5 0 0.5 1 -0.4-0.3-0.2-0.100.10.20.30.4 0.04 K 0.15 K 0.20 K 0.25 K M/Ms 0H (T) 0.002 T/s -1 -0.5 0 0.5 1 -0.4-0.3-0.2-0.100.10.20.30.4 0.280 T/s 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s 0.0005 T/s M/Ms 0H (T) 0.04 K -1 -0.5 0 0.5 1 -0.4-0.3-0.2-0.100.10.20.30.4 0.04 K 0.15 K 0.20 K 0.25 K M/Ms 0H (T) 0.002 T/sa) b) Figure 4-10. Magnetization ( M ) vs. magnetic field ( H ) hysteresis loops for a single crystal of complex 9; (a) at the indicated sweeping rates at 0.04 K, and (b) at the indicated temperatures and a fi xed sweep rate of 0.002 T/s. M is normalized to its saturation value, Ms Additionally, these hyste resis loops display clear steps at periodic intervals which arise due to quantum tunneling of the magne tization (QTM). Thus, since complex 9 displayed hysteresis loops with increasing coercivities with decreasing temperatures, and steps in the loops arising from QTM, it is an SMM, though the effect ive barrier to magnetization relaxation is very small for this complex, as can be evidenced from the temperatures below which the loops start appearing (ca. 0.25 K). Magnetization decay data and Arrhenius calc ulations gave a value of 1.4 K for the effective barrier for the reversal of the magnetization direction ( Ueff). This may be compared to the thermodynamic (potential) energy barrier of U = 1.79 K, where U = ( S2 1/4) for half-integer spin systems. Thus, the U is greater than Ueff as is expected, as the barrier calculated using S and D relates the total energy ( U ) needed to go over the barrier and does not take into account the tunne ling taking place. The effective barrier ( Ueff) is a better indicator of the true barrier to magneti zation relaxation as it is based on the kinetics of the process.

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96 4.3.4 Computational Methods Despite the high symmetry and relative simp licity of this system, it is not possible to apply the Kambe method52 to derive an equivalent ope rator expression for the spin Hamiltonian that would allow obtaining its exchange intera ction parameters. However, semiempirical computational using ZILSH ha ve proven extremely valuable in providing relevant information about the magnetic properties of the Fex clusters in the past.61 For this reason, the magnetic interactions in complexes 7, 8, and 9 have been studied using the semiempirical ZILSH method.34 For a detailed explanati on of the ZILSH method, see Appendix C. The ZILSH method uses semiempirical mol ecular orbital calculations to provide estimates of two important quantities: (i ) the exchange inte raction parameter ( JAB) between each pair of interacting centers A and B; and (ii) the average value of the resultant spin couplings, A B. The two values provide complementary information about the system: JAB indicates the preferre d alignment of spins SA and SB, whereas A B reflects the actual alignment of the spins, with a positive value if they are aligned parallel and a negative value if they are aligned antiparallel. The exchange constants, JAB, found for complexes 7, 8, and 9 are given in Table 4-5. The exchange intera ctions around the outer ring of iron ions are antif erromagnetic and relatively large. Of the six interactions between the central ion and thos e in the outer ring, those la beled 1-3, 1-5, and 1-7 are antiferromagnetic and also relatively large. The other three, 1-2, 1-4, and 1-6, are antiferromagnetic but smaller in magnitude. The spin coupling values of the complexes, A B, are presented schematically in Figure 4-11, and their values presented in Tabl e 4-5. Three of the spins in the outer ring are aligned parallel to the spin of the central metal ion, while the other three are aligned

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97 antiparallel to it, leading to a total spin of + 5/2. The parallel spin alignments occur due to spin frustration. The three relevant pathways (1-2, 1-4, and 1-6) are antiferromagnetically coupled, but the couplings are considerably weaker than those of all other pathways, suggesting they could be frustrated. This va lue was calculated to be negative for every pair of adjacent Fe atoms, corresponding to spins that are aligned antiparallel. This is confirmed by the values of B A ABS S J 2 for each complex, which show that the ground state energy is increased by the 1-2, 1-4, a nd 1-6 pathways, and stabilized by all other nonzero interactions. These results clearly i ndicate frustration of the three weaklycoupled exchange pathways and e xplains the nonzero total spin of S = 5/2 ground states in the complexes 7, 8, and 9. The exchange interactions l ead to a ground state with spin of 5/2 for the complexes. Fe1 Fe2 Fe4 Fe5 Fe6 Fe7 Fe3 Fe1 Fe2 Fe4 Fe5 Fe6 Fe7 Fe3 Figure 4-11. Schematic diagram of comple xes, including numbering scheme used in ZILSH calculations, and spin alignmen ts found for the ground state of all three complexes

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98Table 4-5. Exchange constant s, spin couplings in the S = 5/2 ground states, an d contributions to the total energies of the S = 5/2 ground states, -2 JAB {SA SB}, of the complexes 7, 8, and 9. The numbering scheme used is shown in Figure 4-11 Complex 7 8 9 Interaction JAB A {SA SB} B , -2 JAB {SA SB}, JAB A {SA SB}B , -2 JAB {SA SB} JAB A {SA SB}B , -2 JAB {SA SB} 1,2 -15.4 +6.01 +185.4 -20.7 +5.98 +247.4 -19.7 +5.95 +234.5 1,3 -42.7 -6.94 -592.7 -52.7 -7.01 -739.3 -46.5 -6.98 -649.5 1,4 -15.9 +6.01 +190.9 -20.1 +5.94 +238.6 -19.9 +5.95 +236.3 1,5 -42.6 -6.99 -596.3 -48.2 -6.91 -666.3 -46.2 -6.96 -643.6 1,6 -16.5 +6.02 +199.1 -20.3 +5.94 +241.2 -19.9 +5.94 +236.8 1,7 -36.6 -6.98 -622.6 -48.2 -6.92 -666.9 -45.5 -6.94 -632.3 2,3 -36.6 -7.15 -523.4 -50.7 -7.34 -745.0 -44.6 -7.29 -650.2 3,4 -29.1 -6.83 -397.4 -24.3 -6.41 -310.9 -25.1 -6.54 -328.6 4,5 -35.5 -7.14 -506.4 -48.0 -7.35 -705.5 -45.0 -7.31 -657.4 5,6 -26.6 -6.77 -360.9 -25.7 -6.51 -334.4 -25.0 -6.53 -327.0 6,7 -38.6 -7.18 -555.0 -48.5 -7.35 -711.8 -44.6 -7.30 -650.8 7,2 -27.5 -6.75 -371.6 -25.4 -6.52 -331.2 -25.3 -6.56 -332.2 a From ZILSH calculations. b From diagonalization of the Heisenberg Hamiltonian All energy parameters are given in cm-1. Interactions not listed have exchange constants approximately equal to zero

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99 Block arrows in Figure 4-11 depict the spin alignments in this scheme, but it must be remembered that the assignment of a spin moment to each metal, represented by an arrow pointing up or down, is intuitive and us eful but not rigorously correct. The parallel spin alignments occur due to spin frustrati on. The ground states for the complexes appear to be well-isolated, separated from th e first excited state by more than 100 cm-1 in each case (Table 4-6). It must be noted, however, that the sparse matrix technique used for diagonalizing the HSH considers only the lowe st-energy state of each spin. Thus there could be other low-lying excited states with the same total spin as the ground state with lower energies. Table 4-6. Ground state spins, local z-components of spin, Mi, and energies (cm-1) of the first excited states for complexes 7, 8, and 9 found with ZILSH calculations Complex 7 8 9 M1 1.68 1.65 1.63 M2 2.00 1.98 1.99 M3 -1.72 -1.70 -1.70 M4 1.99 2.00 1.99 M5 -1.72 -1.70 -1.70 M6 1.99 1.99 1.99 M7 -1.72 -1.70 -1.70 Spin and energy, ground state 5/2, 0.0 5/2, 0.0 5/2, 0.0 Spin and energy, first excited st ate 7/2, 168.3 7/2, 192.6 7/2, 179.8 4.3.5 Single-Crystal, High-Frequency EPR (HFEPR) Spectroscopy of Complex 9 In contrast to the information obtained by magnetic susceptibility studies, from which we can determine the ground state,106 EPR spectroscopy provides direct information of transition energies between stat es and allows determining values such as D and S directly. One limitation of EPR at conve ntional frequencies (X-band: 9 GHz; Qband: 35 GHz) is that it cannot be applied to compounds with integer spin ground states or half integer spin ground states with large anisotropies. The former compounds are frequently “silent” to EPR, whereas the latter often allow just a partial detection of the

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100 spectra. The development of high field (up to 30 T) and high frequency (100 GHz) EPR (HFEPR) has made it possible to obser ve these systems and obtain valuable information about them. It is possible to observe dire ct transitions between the ze ro-field split sublevels of the high ground state spin. HFEPR has been used to characterize the ground state of several high-spin complexes, and wi ll be used here to verify the S = 5/2 ground state and confirm the negative D value of complex 9. This can be done because detailed analysis of the EPR spectra at various frequencies a nd angles gives direct access to the energy differences between spin levels and because changes in the relative intensities of EPR peaks reflect changes in the Boltzmann populatio n of states. Thus, the sign and precise values of the zero-field splitting parameters can be determined, and this then enables a precise determination of the spin Hamiltonian pa rameters. In an ideal case, the spin of the ground state can be determined by simply counting the number of peaks in the EPR spectrum, and the zero-field splitting pa rameter can be evaluated from the spacing between successive peaks. Complex 9 exhibits SMM-like EPR spectra. Fi g. 4-12 shows singl e crystal data obtained at 51.8 GHz and at di fferent temperatures, with th e dc magnetic field applied within the hard-plane. A total of five main peaks are observed, denoted by numbers 1 to 5, thus confirming the S = 5/2 ground state of the molecu le. Another set of three weaker peaks can be seen as shoulders on three of the main peaks (labeled with subscripts x ). There are several possible explanations for th ese weaker peaks, including: a low lying S = 3/2 excited state; inter-molecular exchange in teractions; or disorder -induced strains in the sample leading to different molecular species.107 ZILSH calculations seem to exclude the

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101 possibility of low lying excited states. Th e inset to Figure 4-12 shows the Zeeman diagram for a spin S = 5/2 system with a negative D va lue and the field applied within the hard plane. The five observe d transitions (1 to 5) are shown for two different EPR frequencies (51.8 and 117 GHz). Because th e energy differences between Zeeman-split levels are much smaller at lower fields, less thermal energy is required to populate the higher-lying levels within the S = 5/2 state. Higher freque ncy EPR spectra (not shown here) taken at 117.8 GHz s how only peak at 1.3 K. 1.21.62.02.42.8 01234567 -500 -250 0 250 500 (3)x(2)x(1)x(5) (4) (3) (2) (1) Transmission (arb. units offset)Magnetic Field (Tesla) 15.0 K 10.0 K 6.0 K 3.0 K 2.5 K 2.0 K5 4 3 2 1 117 GHz51.8 GHzB// x f (GHz) Figure 4-12. HFEPR spectra of th e crystal taken at 51.8 GHz, at temperatures from 2.0 to 15.0 K. Inset is the simulated Zeeman energy diagram in the hard-plane Angle-dependent measurements from the c -axis to ab -plane were performed at 6 K, and frequencies of 51.8 GHz and 179.8 GHz, as shown in Fig. 4-13. Superimposed on the data points are simulations using the followi ng simple Hamiltonian (the parameters are listed in the figure): = D z 2 + gBB . The solid blue squares represent the transition from the ground state [labeled (1) in Fig. 412]; the red circles co rrespond to transition

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102 (2). The two dashed lines indicate the isotropic positions (D = 0, g = 2.00). The fact that the peaks shift approximately twice as far to the low field side of the g = 2.00 reference, as compared to the high field side, implies a uniaxial anisotropy with a negative D parameter. Indeed, the high frequency data fit very well to a (1 3cos2) angle dependence, which is expected for a SMM in the high field limit. The angle corresponding to = 0o marks the easy axis orientation. 0306090120150180 0 1 2 3 4 5 6 7 51.8 GHz 117.8 GHz Magnetic field (tesla)Angle (degrees) m = 5/2 to 3/2 m = 3/2 to 2/2 D = 3.6 cm; B0 4 = 70 cm; g = 2.00(1) 0306090120150180 0 1 2 3 4 5 6 7 51.8 GHz 117.8 GHz Magnetic field (tesla)Angle (degrees) m = 5/2 to 3/2 m = 3/2 to 2/2 D = 3.6 cm; B0 4 = 70 cm; g = 2.00(1) Figure 4-13. Plot of the HFEPR peak positions from angle-dependent measurements at 51.8 GHz and 179.8 GHz with fields rotati ng ~ 200 from the c-axis to the abplane Precise determination of the spin Hamiltonian parameters D and g is achieved through EPR spectra taken at va rious frequencies (50 to 20 0 GHz) for both the easy-axis and hard-plane orientations, as shown in Fig. 4-14. Simulati ons for both the easy-axis and hard-plane diagrams suggest that the system is best described with D = 0.36 cm 1 and g = 2.00(1). These parameters were used to simulate the angle-dependent EPR peak positions at 179.8 GHz and 51.8 GHz, as shown in Fig. 4-13.

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103 It is worth noting that the line width of th e easy-axis EPR peak (inset of Fig. 4-14) is much sharper than the hard-plane on es. The easy-axis line width for complex 9 is ~0.01 T, which is considerably narrower than other well studied SMMs.107, 108 The extraordinary sharpness of the EPR spectra s eems to confirm the reduced decoherence in this system (T2 3 ns) relative to other known S MMs, thus making it an interesting candidate for studies of coherent quantum magnetization dynamics. 0 50 100 150 200 250 300 012345678 0 50 100 150 200 250 2.642.702.76 D = -3.6 cmg = 2.00(1) Frequency (GHz) easy axis data hard plane data Magnetic field (tesla)117.8 GHz T = 1.3 K -0.36 cm-1 0 50 100 150 200 250 300 012345678 0 50 100 150 200 250 2.642.702.76 D = -3.6 cmg = 2.00(1) Frequency (GHz) easy axis data hard plane data Magnetic field (tesla)117.8 GHz T = 1.3 K -0.36 cm-1 Figure 4-14. Energy difference diagrams constructed from frequency-dependent measurements of both the easy-axis and hard-plane. Solid lines are the simulations with given parameters. Inset shows a typical easy-axis EPR peak of this crystal whose line wi dth is only few hundred gausses

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104 4.4 Conclusions The synthetic routes developed in this ch apter have proven to be useful in the preparation of heptanuclear compounds from lower nuclearity starti ng materials. A new family of unusually odd-numbered iron comple xes has been obtained. All of them have the same nuclearity, Fe7, and one of these complexes functions a new half-integer singlemolecule magnet. The magnetic behavior of these new co mpounds has been quantitatively and qualitatively described using a combinati on of various methods. Detailed magnetic susceptibility studies have established that all of these complexes possess an S = 5/2 ground state spin. In addition, high frequency EP R and semiempirical calculations led to the same conclusion; the ground state spin is 5/2. Also these, together with the magnetization vs. field measurements indicate the axial zero field splitting parameter D, to be positive in complexes 7 and 8, and negative in 9. The semiempirical calculations not only confirm all the experimental results, th ey also afford estimation of the exchange constants between the metal ions. Finally, studies on complex 9 of magnetization vs. time decay, to obtain relaxation kinetic data th at would allow an Arrhenius plot to be constructed, from which could be determin ed the effective barrier to magnetization relaxation ( Ueff), would also be very useful. In any event, complexes 7-9 described in this work are unusual and represent important new additions to polynuclear iron complexes, which continue to provide invaluable insights on the magnetic propert ies of molecular nanomagnets. Although all the complexes are structurally very similar, only complex 9 functions as a SMM. Of course, this merely emphasizes how comp licated and unpredictable are the magnetic properties of these molecular complexes. Nevertheless, the work herein reinforces the

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105 belief that the “bottom-up approach” to nanomagnetism continues to spring new surprises, as this field further develops.

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106 CHAPTER 5 MANGANESE COMPLEXES INCORPORATING AZIDES: ZERO, ONE AND TWO DIMENSIONAL STRUCTURES 5.1 Introduction The preparation of coordination polymers,109, 110 which are infinite systems comprising metal ions and organic ligands linked through covalent bonds and other weak chemical bonds, is the basis of the metal-orga nic coordination networ ks or metal-organic frameworks (MOFs) chemistry. These captivati ng structures together with the potential application of the supramolecula r architectures have attracted intense interest. They are promising materials for a pplications in catalysis,111 electrical conducting materials,112 sensor materials,113 liquid crystals114 and molecular magnetic materials.115 There are four different kinds of building bricks used fo r the construction of MOFs, which crucially influence the final propertie s of the compounds: organic ligands, which act as bridging organic groups between the meta l ions; metal ions, that are involved in the structure depending on their size, hardness/soft ness, ligand-field stab ilization energy and coordination geometries; counter ions, which are present in the structure when neutral ligands are used; and solvent molecules that may co-crystallize, increasing the number of possible weak interactions in the final solid-st ate packing, and which can also act as guest molecules in the vacant spaces between the polymer construct. In this dissertation it has been demonstrated that mdaH2 acts as a versatile chelating and bridging ligand. Additionally, the use of triethanolamine (teaH3), another flexible ligand in inorganic chemistry, has also prove n to be valuable for the syntheses of new

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107 complexes of different topologies and nuclearities in manganese chemistry.116 The combination of these types of ligands and azides was thought a possi ble route to both complexes with potentially extr emely large spin ground states,73 and also to MOFs. Along these lines, compounds reported to da te mostly incorporate neutral organic coligands. Thus, reactions involving azide s and charged ligands are very scarce.117 Synthesizing high-dimensional compounds in tegrating azides and negatively charged ligands represents a new challenge for researchers involved in this field. Azides are good candidates for the de sign of magnetic c oordination polymers,118 as several 1-, 2and 3-D complexes have been reported119 wherein azides act as extremely versatile ligands, and as mediators of magne tic exchange coupling. In fact, the azide ligand has several coordination modes that pr ovide a variety of exchange interaction. However, the two most common bridging mode s of the azide ligand are: (i) the 1,3-N3 bridge (end-to-end, EE) associated with antiferromagnetic coup ling and (ii) 1,1-N3 bridge (end-on, EO) associated with ferroma gnetic exchange (Figure 5-1). Combined EO + EE links,120 and alternating bridges121 have also been reported in azide containing compounds. End-to-End, EE M M M M End-on, EO a) b) End-to-End, EE M M M M End-on, EO a) b) Figure5-1. Representation of the two t ypical coordination modes of the azide (N3 -) bridging ligand

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108 Usually, ligands with Nor O-donors are used in th e design and synthesis of MOFs122. In this chapter, we explore reacti ons involving the flexible tripodal and tetrapodal ligands, mdaH2 and teaH3, (both containing Nand Odonors) in the presence of the azide ligand, with various manganese metal salts. Novel st ructures and magnetic properties are expected to ar ise through these reactions because of the diversity of bridging modes of the azide and the tripoda l and tetrapodal ligands. Additionally, the efficient mediating magnetic in teraction of the groups, especially the azide groups has led to one of these complexes to function as a single-molecule magnet. 5.2 Experimental Section 5.2.1 Syntheses All manipulations were performed under aerobic conditions us ing materials as received, except where otherwise noted. Caution: Azide metal complexes are potentially explosive . Only a small amount of material should be prepared, and it should be handled with caution. (HNEt3)[Mn7(mda)6Cl6]MeCNEt2O (10). To a stirred solution of MnCl2H2O (0.10 g, 1.0 mmol) in MeCN (20 mL) and NEt3 (70.0 L, 0.5 mmol) was added mdaH2 (58.0 L, 0.5 mmol). The resulting dark brow n solution was refluxed for two hours and left undisturbed overnight. Then, it was filtere d and the filtrate slowly diffused with Et2O, dark crystals of 10 slowly grew after 24 hours. These cr ystals were collect ed by filtration, washed with Et2O (3 x 10mL), and dried in air. Th e yield was 24%. Elemental analysis for (HNEt3)[Mn7(mda)6Cl6] (C36H82Mn7N7O12); Experimental (calcu lated): C, 30.83; H, 5.89; N, 6.99. Found: C, 30.44; H, 6.10; N, 6.58 %. Selected FT-IR data (KBr, cm-1): 2056 (s), 1652 (w), 1558 (w), 1456 (m), 1070 (s), 1039 (m), 1002 (w), 913 (w), 890 (m), 667 (w), 647 (w), 596 (w), 526 (w).

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109 (HNEt3)[Mn7(mda)6(N3)6] (11). Method A. To a stirred solution of MnCl2H2O (0.10 g, 1.0 mmol) in MeCN/MeOH (20:1 mL) and NEt3 (70.0 L, 0.5 mmol) was added mdaH2 (58.0 L, 0.5 mmol) and NaN3 (0.13g, 2.0 mmol). The resulting dark brown solution was stirred overnight, a nd then layered with ether. Af ter several days, dark black crystals of 11 were collected by filtration, washed with Et2O (2 x 15ml), and dried in air. The yield was ~20 %. Elemental Analysis (HNEt3)[Mn7(mda)6(N3)6]MeOH (C37H86Mn7N25O13); Experimental (calculated): C, 30.15; H, 5.88; N, 23.76. Found: C, 30.34; H, 6.08; N, 23.44 %. Selected FT-IR data (KBr, cm-1): 2058 (s), 1630 (m), 1616 (m), 1575 (m), 1540 (m), 1456 (m), 1419 (m), 1395 (m), 1296 (w), 1261 (w), 1205 (w), 1160 (w), 1066 (m), 1033 (m), 1002 (m), 890 (m), 802 (w), 746 (w), 667 (m), 647 (m), 596 (m), 526 (m), 442 (w). Method B. To a stirred solution of 10 (7.00 mg, 10.0 mmol) in CH2Cl2/MeOH (30:3 mL), NaN3 (0.65 mL, 10.0 mmol) was added. The resulting dark brown solution was stirred for one-two hours, filter ed and the filtrate layered with Et2O. After several days, dark red crystals of 11 were collected by filtration, wa shed with ether and dried in air; yield ~13 %. The product was identified as complex 11 by IR spectroscopic comparison with material from Method A. {Na(MeOH)3[Mn7(mda)6(N3)6]}n (12). To a solution of Mn(acac)3 (0.50 g, 1.5 mmol) in a mixture MeCN/MeOH (20/20 mL), mdaH2 (0.23 mL, 2.0 mmol) and NaN3 (0.12 g, 1.8 mmol) were added. After bei ng stirred for six hours, the resulting solution was filtered and the filtrate slow diffused with Et2O, dark crystals of 12 slowly grew after four days. These were air-dried and isolat ed in 22% yield. Elemental analysis for Na(HOMe)3[Mn7(mda)6(N3)6]MeOH (C34H82Mn7NaN24O16); Experimental (calculated):

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110 C, 30.12; H, 5.78; N, 23.56. Found: C, 30.44; H, 6.04; N, 23.28 %. Selected FT-IR data (KBr, cm-1): 2056 (s), 1594 (m), 1518 (m), 1456 (m), 1401 (m), 1336 (m), 1261 (m), 1202 (w), 1066 (m), 1032 (m), 999 (m), 912 (w), 888 (m), 760 (w), 735 (w), 670 (w), 644 (w), 580 (m), 531 (m), 442 (w). [Mn18O11(OH)(N3)12(tea)3(teaH)3(OMe)( MeOH)]CH2Cl2Et2O (13). To a stirred solution of Mn(ClO4)2H2O (0.5 g, 1.4 mmol) and teaH3 (0.18 mL, 1.3 mmol) in CH2Cl2 (20 mL) was added a solution of NaN3 (0.13 g, 2.0 mmol) in MeOH (20 mL). The resulting dark brown solution was stirre d for one hour. And slow diffused with Et2O. After a few days crystals of 13CH2Cl2Et2O slowly grew over, in a yield of 32%. Elemental analysis for [Mn18O11(OH)(N3)12(tea)3(teaH)3(OMe)(MeOH)] (C32H83Mn18N42O32); Experimental (calculated): C, 15.03; H, 3.26; N, 23.01. Found: C, 15.20; H, 3.37; N, 22.78 %. Selected FT-IR data (KBr, cm-1): 2061 (s), 1634 (w), 1457 (w), 1395 (w), 1334 (w), 1310 (w), 1281 (w), 1155 (w), 1067 (m), 1031 (m), 903 (m), 653 (m), 616 (m), 576 (m), 531 (m), 476 (m), 427 (w). [Mn31O20(O2CMe)23(tea)2(dea)2(N3)4(OMe)2(MeOH)6]nMeCN (14). A slurry solution of Mn(ClO4)2H2O (0.10 g, 0.27 mmol) and Mn(O2CMe)2H2O (0.61 g, 2.50 mmol) in MeCN (40 mL) was treated with teaH3 (3.90 L, 0.29 mmol). Then a solution of NaN3 (0.08 g, 1.37 mmol) in MeOH (5 mL) was slowly added, and the resulting mixture was left stirring overnight. The soluti on was filtered and slow evaporation of the resulting solution gave brown crystals of 1426MeCN over two weeks. The crystals were collected by filtration and they were air-d ried. The yield was 37 % yield. Elemental analysis for [Mn31O20(O2CMe)23(tea)2(dea)2(N3)4(OMe)6(MeOH)2]10MeCN4H2O (C94H175Mn31N26O88); Experimental (calculated): C, 23.30; H, 3.64; N, 7.51. Found: C,

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111 23.68; H, 3.62; N, 7.34 %. Selected FT-IR data (KBr, cm-1): 2066 (s), 1567 (s), 1417 (s), 1342 (m), 1107 (m), 1060 (m), 1052 (m), 948 (w), 899 (w), 706 (s), 664 (s), 621 (s), 591 (s), 503 (s), 462 (s). 5.2.2 X-Ray Crystallography Suitable crystals of 10MeCNEt2O, 11, 12, 13CH2Cl2Et2O, 1426MeCN were selected from the bulk samples, maintained in mother liquor to avoid solvent loss, attached to the tips of a gla ss capillary and transf erred to the goniostat, where they were cooled to 173 K for characterization and data collection. Data were collected at 173 K on a Siemens SMART PLATFORM equipped with a CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were refined using up to 8192 reflections. A full sphere of data (1850 frames) was collected using the -scan method (0.3 frame width). The first 50 frames were remeasured at the end of data collection to monitor instrument and crysta l stability (maximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces. The structures were solved by the Direct Methods in SHELXTL531, and refined on F2 using full-matrix least-squares. The non-H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal pos itions and were ridi ng on their respective carbon atoms. Complexes 10, 12 and 13 crystallize in the monoclinic space group P 21/ c . For complex 10, the asymmetric unit consists of the Mn7 cluster, one triethylamino cation, water and a methanol molecule. The latter tw o molecules could not be modeled properly, thus program SQUEEZE,32 a part of the PLATON33 package of crystallographic

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112 software, was used to calculate the solvent disorder area and remove its contribution to the overall intensity data. A total of 627 para meters were refined in the final cycle of refinement using 39381 reflections with I > 2(I) to yield R1 and wR2 of 6.55% and 16.78%, respectively. Crystallogr aphic unit cell and structure so lution data are listed in Table 5-1. Preliminary data of complex 11 was collected, but the data showed the structure to be similar to complex 10, with the difference being the re placement of chloride by azides, so further refinement structure was not performed. Complex 12 crystallizes in the monoclinic space group C c . The asymmetric unit of complex 12 consists of a Mn7 cluster, a sodium cation and four methanol molecules. All four hydroxyl protons of the methanol mo lecules were obtained from a Difference Fourier map and refined freely. One of the azide ligands has its terminal two nitrogen atoms disordered and was refined in two parts. A total of 758 parameters were refined in the final cycle of refinement using 7270 reflections with I > 2(I) to yield R1 and wR2 of 4.29 and 9.90%, respectively. Complex 13 crystallizes in the triclinic P 1 space group. This complex consists of the Mn18 cluster, two dichloromethane molecule s and four diethylether molecules. The O32-C38 methoxy ligand is disordered agai nst an azide in the same position and was refined as a methoxy and only the terminal N of the azide. The other two N atoms could not be resolved from the methoxy atoms. The site occupation factor of N3, from the partial azide, was refined but finally fixed in th e last refinement cycles to a value of 20%. The solvent molecules were disordered and c ould not be modeled properly, thus program SQUEEZE, was used to calculate the solvent disorder area and remove its contribution to

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113 the overall intensity data. A total of 1184 para meters were refined in the final cycle of refinement using 35186 reflections with I > 2(I) to yield R1 and wR2 of 5.77 and 14.33%, respectively. For complex 14, the asymmetric unit consists of Mn31 cluster units forming infinite chains that are further linked through azide bridges to produce infinite sheets in the ac plane. The asymmetric unit also contains 26 acetonitrile solvent molecules which were disordered and could not be modeled properl y, thus program SQUEEZE, was used to calculate the solvent disorder area and rem ove its contribution to the overall intensity data. A total of 1846 parameters were refine d in the final cycle of refinement using 69613 reflections with I > 2(I) to yield R1 and wR2 of 7.76 and 18.71%, respectively.

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114Table 5-1. Crystallographic data for complex10, complex 12, complex 13 and complex 14 Parameter 10MeCNEt2O 12 13CH2Cl2Et2O 1426MeCN formulaa C46H105Mn7N8O14 C34H82Mn7NaN24O16 C56H127Cl4Mn18N42O36 C126H215Mn31N42O84 fw, g mol-1 1591.68 1490.81 3095.72 5365.54 space group P 21/ c Cc P 1 P 21/ c a , 11.1009(7) 17.2034(8) 15.3132(2) 35.759(4) b , 19.0949(12) 15.4286(7) 18.3122(11) 14.8904(16) c , 29.2126(19) 22.9340(11) 21.422(2) 32.943(4) , deg 90.00 90.00 68.092(2) 90.00 , deg 97.502(2) 98.398(1) 79.91(2) 92.562(2) , deg 90.00 90.00 74.134(2) 90.00 V , 3 6139.2(7) 6022.0(5) 5342.9(6) 17524(3) Z 4 4 2 4 T , K 173(2) 173(2) 173(2) 173(2) mm-1 1.716 1.507 2.238 2.254 radiation, b 0.71073 0.71073 0.71073 0.71073 calc, g cm-3 1.642 1.644 1.928 2.034 R 1 ( wR 2) %c , d 6.55 (16.78) 4.29 (9.90) 5.77 (14.73) 7.76 (18.71) a Including solvent molecules. b Graphite monochromator. c R 1 = || Fo| – | Fc|| / | Fo|. d wR 2 = [w ( Fo 2 Fc 2)2] / [ w Fo 2)2]]1/2 where S = [[ w ( Fo 2 – Fc 2)2] / ( n p )]1/2, w = 1/[2( Fo 2) + ( m * p )2 + n * p ], p = [max( Fo 2, 0) + 2* Fc 2]/3, and m and n are constants

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115 5.3 Results and Discussion 5.3.1 Syntheses As a continuation of the studies described in Chapter 2, and in an attempt to obtain new manganese aggregates, the reactivity of different starting materials has been explored,in the presence of azides, an d certain tripodal ligands. The complex (HNEt3)[Mn7(mda)6Cl6] (10) was obtained from a reaction employing MnCl2 4H2O as the manganese source. Refluxing of 1 equivalent of MnCl2 4H2O with 2 equivalents of mdaH2 and 2 equivalents of NEt3 in a solution of MeCN for two hours gave a solution from which was obtained (HNEt3)[Mn7(mda)6Cl6] (10) in 24% yield. The formation of 10 is summarized in Eq. 5-1 and involves oxida tion by air of manganese centers from an average oxidation state of +2 in the MnCl2 starting material to +2.4 in the MnII 4MnIII 3 product. Complex 10 can also be obtained from the reaction of MnCl2, mdaH2 and NEt3 in a 1:3:3 ratio. 7 MnCl2 + 6 mdaH2 + 4 NEt3 (HNEt3)[Mn7(mda)6Cl6] + 8 HCl + 3 HNEt3 + + 3 e(5-1) With the aim to introduce a second liga nd to the reaction system, which might change the identity of the pr oduct and/or its magnetic propert ies, sodium azide was added to the reaction mixture. A similar compound wa s obtained in which the terminal chlorides of 10 had been replaced by azides, the change did not affect the magnetic properties or the structure (see later). For this reason, only complex 10 will be described further. The reaction of MnCl2, mdaH2, NaN3 and NEt3 was conducted employing different ratios, but the highest yield was obtained in a 1:2:2:1 ratio. This reaction is summarized in Eq. 5-2. 7 MnCl2 + 6 mdaH2 + 6 NaN3 + 4 NEt3 (HNEt3)[Mn7(mda)6(N3)6] + 6 NaCl + 8 HCl + 3 HNEt3 + + 3 e(5-2)

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116 Similar reactions under a variety of condi tions and with different Mn starting materials were also explored. The r eaction of 1 equivalent of Mn(acac)3 with 1 equivalent of mdaH2 and 1 equivalent of sodium azide in a mixture of ace tonitrile/ methanol gave black crystals of {Na(MeOH)3[Mn7(mda)6(N3)6]}n in 22 % yield. In this case a reduction of some MnIII to MnII was observed, or disproportionation of MnIII has occurred. Reactions were also performed with anothe r alcohol-based chelat e, triethanolamine (teaH3) in reactions involving azides. The r eaction between one equivalent each of Mn(ClO4)2, teaH3, and NaN3 in a mixture of solvents (CH2Cl2/MeOH) [Mn18O11(OH)(N3)12(tea)3(teaH)3(OMe)(HOMe)]CH2Cl2Et2O (13) complex in 32 % gave yield (Eq. 5-3). 18 Mn(ClO4)2 + 12 NaN3 + 6 teaH3 + 2 MeOH + 12 H2O [Mn18O11(OH)(N3)12(tea)3(teaH)3(OMe)(HOMe)]+ 12 NaClO4 + 24 ClO4 + 39 H+ + 24 e(5-3) Complex 13 is mixed-valence. There is oxidation of MnII by atmospheric oxygen. Since oxidation of only some of the MnII occurs during the re action, it was also investigated whethe r starting with a MnIII reagent might lead to a different product. However, different reactions using [Mn2O(O2CPh)2(N3)2(bipy)2] (MnIII 2),64 or the wellknown [Mn3O(O2CMe)6py3](ClO4) (MnIII 3)28a as the Mn source did not give any isolable product. Similar reactions using Mn(O2CMe)2 instead of Mn(ClO4)2 were conducted, a reaction with a mixture of Mn(ClO4)2 and Mn(O2CMe)2 as starting materials was performed. Thus, the reaction betw een 1 equivalent each of Mn(ClO4)2, Mn(O2CMe)2, teaH3 and NaN3 in a mixture of solvents (MeCN/MeOH) led to the isolation in 37 %

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117 yield of [Mn31O20(N3)4(O2CMe)23(tea)2(dea)2(OMe)5(MeOH)3]26MeCN (14). The Mn31 complex has two doubly deprotonated diethanola mine (dea). The presence of dea can be explained because deaH2 has been postulated as a contaminant in the teaH3 starting material or because there is a N-C bond cleavage leading to deaH2. The isolated product is again mixed-valence; and its formation is summarized in Eq. 5-4. Again, there is oxidation of MnII by (presumably) atmospheric oxygen. 8 Mn(ClO4)2 + 23 Mn(O2CMe)2 + 4 NaN3 + 2 teaH3 +2 deaH2 + 20 H2O [Mn31O20(N3)4(O2CMe)23(tea)2(dea)2(OMe)6(MeOH)2] + 4 NaClO4 + 23 MeCO2 + 12 ClO4 + 48 H+ + 52 e(5-4) 5.3.2 Description of Structures 5.3.2.1 Structure of (HNEt3)[Mn7(mda)6Cl6] (10) A view of the structure of the anion of (HNEt3)[Mn7(mda)6Cl6] (10) is shown in Figure 5-2, and selected metr ic parameters are listed in Table A-10. The anion of complex 10 consists of six Mn atoms (Mn2, Mn3, Mn4, Mn5, Mn6, Mn7) arranged in a ring around a central Mn (Mn1) atom, with ligation provided by six mda2 ligands and six terminal chloride ions. Each mda2 group contains one 2-alkoxide arm (O7, O8, O9, O10, O11 and O12) and one 3-alkoxide arm (O1, O2, O3, O4, O5 and O6), the latter bridging the outer Mn atoms with th e central Mn. Note that all mda2groups alternate the Mn7 plane, and all mda2alkoxide groups bridge a MnIIMnIII pair; this tendency has been observed previously in structures of the mda2ligand.90,123 The core of the molecule is planar and possesses partial cubane Mn3O4 units in the core, which are fused along common faces.

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118 Mn1 Mn2 Mn3 Mn4 Mn5 Mn6 Mn7 Cl1 Cl2 Cl3 Cl4 Cl5 Cl6 N1 N2 N3 N4 N5 N6 O2 O9 O3 O8 O6 O7 O4 O5 O12 O11 O1 O10 b) a) Mn1 Mn2 Mn3 Mn4 Mn5 Mn6 Mn7 Cl1 Cl2 Cl3 Cl4 Cl5 Cl6 N1 N2 N3 N4 N5 N6 O2 O9 O3 O8 O6 O7 O4 O5 O12 O11 O1 O10 Mn1 Mn2 Mn3 Mn4 Mn5 Mn6 Mn7 Cl1 Cl2 Cl3 Cl4 Cl5 Cl6 N1 N2 N3 N4 N5 N6 O2 O9 O3 O8 O6 O7 O4 O5 O12 O11 O1 O10 b) a) Figure 5-2. ORTEP representation in PovR ay format of the anion of complex 10 (a): [Mn7(mda)6Cl6], where the relative disposi tion of the Jahn-Teller elongation axes are indicated as solid black bonds. (b) representation of complex 10 by polyhedra. MnIII green; MnII orange; O red; N blue; Cl dark green, C gray. H atoms have been omitted for clarity All Mn are six-coordinate and the MnII or MnIII oxidation state assignments were established by consideration of bond distances, and bond-valence sum (BVS) calculations (Table 5-2).46, 47 The presence of Jahn-Teller (JT) elonga tion axes at three of the Mn ions, as expected for high-spin MnIII in near-octahedral geometry, helps to confirm the MnIII oxidation state assignments; the thr ee JT axes contain three of the 3-O mda2atoms (O2, O3, O4) and three terminal chlorine i ons (solid black bonds in Figure 5-2). Several heptanuclear Mn complexes have previously been synthesized; many have the same formulation of MnII 4MnIII 3: [Mn7(teaH)3(tea)3](ClO4)2,116b where teaH3 is triethanolamine; NEt4[Mn7(OH)3(hmp)9Cl3]Cl(MnCl4), 124 [Mn7(OH)3(hmp)9Cl3]Cl(ClO4),124 where hmpH = 2-hydroxymethyl pyridine. A structurally related complex but consisting of MnII 3MnIII 4 is [Mn7(OMe)12(dbm)6]125 , which possesses an S = 17/2 ground state.

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119 Table 5-2. Bond valence sum calculationsa for complex 10 Atom Mn2+ Mn3+ Mn4+ Mn(1) 1.805 1.651 1.733 Mn(2) 2.006 1.897 1.931 Mn(3) 3.065 2.873 2.944 Mn(4) 1.987 1.873 1.911 Mn(5) 3.034 2.845 2.457 Mn(6) 2.034 1.924 1.958 Mn(7) 3.011 2.818 2.892 a The underlined value is the one closest to the actual charge for which it was calculated. The oxidation state of a particular atom can be taken as the nearest whole number to the underlined value N3 N3 Figure 5-3. ORTEP representation in PovR ay format of the anion of complex 10: [Mn7(mda)6Cl6], and the complex 11 [Mn7(mda)6(N3)6]-. The relative disposition of the Jahn-Te ller elongation axes are indicated as solid black bonds. MnIII green; MnII orange; O red; N blue; Cl darkgreen, C gray. H atoms have been omitted for clarity As stated earlier, the same reaction that gives complex 10 but in the presence of sodium azide, resulted in complex 11, identical to complex 10 but with six terminal azides rather than chlorine ions (Figure 5-3). 5.3.2.2 Structure of {Na(HOMe)3[Mn7(mda)6(N3)6]}n (12) An ORTEP labeled structure of {Na(HOMe)3[Mn7(mda)6(N3)6]}n (12) is shown in Figure 5-4, and selected metr ic parameters are listed in Table A-11. The anion of

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120 Na N22 N23 N24 N1 N2 N3 Mn1 Mn3 Mn2 Mn4 Mn6 Mn5 Mn7 a) b) O13 O15 O14 Na N22 N23 N24 N1 N2 N3 Mn1 Mn3 Mn2 Mn4 Mn6 Mn5 Mn7 a) b) O13 O15 O14 Figure 5-4. ORTEP representation in PovRay format of complex 12 (a), {Na(MeOH)3[Mn7(mda)6(N3)6]}. (b) ORTEP representa tion in PovRay format of the complex 12 along the axis. MnIII green; MnII orange; O red; N blue; Na purple, C gray. H atoms have been omitted for clarity complex 12 has the same structure as complex 10, except the chlorine ions which have been substituted by azide ligands. The Mn7 core of the molecule, same as 11, is planar again and comprises Mn3O4 partial cubane units fused along common faces. One of the azide ligands (N22, N23 and N24) links a MnII ion (Mn7) of one cluster to a sodium ion. This sodium ion in turn is linked via a nother azide ligand (N1, N2 and N3) to a MnIII ion (Mn1) of an adjacent Mn7 cluster, thereby forming an infinite chain along the b axis

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121 (Figure 5-4). Additionally, each sodium ion is terminally ligated by three methanol molecules (O13, O14, O15). The MnII or MnIII oxidation state assignments were established by consideration of bond distances, and bond-valence sum (BVS) calculations (Table 5-4).46, 47 The MnIII JT axes are located on three of the 3-O mda2(N4, N13, N20) atoms. Table 5-3. Bond valence sum calculationsa for complex 12 Atom Mn2+ Mn3+ Mn4+ Mn(1) 3.128 2.911 2.975 Mn(2) 2.036 1.903 1.932 Mn(3) 1.960 1.831 1.861 Mn(4) 2.322 2.202 2.254 Mn(5) 3.191 2.992 2.763 Mn(6) 3.133 2.916 2.981 Mn(7) 2.347 2.233 2.264 aThe underlined value is the one closest to the actual charge for which it was calculated. The oxidation state of a particular atom can be taken as the nearest whole number to the underlined value 5.3.2.3 Structure of [Mn18O11(OH)(N3)12(tea)3(teaH)3(OMe)(HOMe)] (13) Two views of the structure of [Mn18O11(OH)(N3)12(tea)3(teaH)3(OMe)(MeOH)] (13) are shown in Figure 5-5a, and selected metr ic parameters are listed in Table A-12. The core was held together by seven 4-O2(O5, O8, O16, O17, O18, O19 and O21), four 3-O2(O4, O6, O20 and O22), one 3 -OH(O7), and three chelating/bridging tea3(O1/O2/O3/N7, O9/O10/O11/N7, O 23/O24/O25/N22) and three teaH2(O12/O13/O14/N29, O26/O27/O 28/N21, O29/O30/O31/N45).

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122 a)b) a)b) Figure 5-5. ORTEP representation in PovRay format of complex 13 (a). Core representation of complex 13 (b). MnIII green; MnII orange; O red; N blue; C gray. H atoms have been omitted for clarity The core (Figure 5-5) may be dissected into three layers, arranged with an ABC disposition. All layers are formed by fused [Mn3O] units. Examination of layers separately, they can better be described as: layer A is a MnIII 4 rhombus unit (Mn1 Mn4); layer B is a MnIII 6 (Mn5 Mn10) triangle comprising three corner-sharing MnIII 3 triangles; and layer C is a MnIII 5MnII 3 (Mn11 Mn18) motif. Layer A has the structure seen in some Mn4 defect-dicubane complexes (see Chapter two).126 Also, layer C has the motif of the Mn7 complexes described earlier, but with an extrinsic MnII ion (Mn18) attached via a 3-O2(O17 in Figure 5-6). Each layer is held together and linked to its neighboring layers by a combina tion of oxide, alkoxide, and / or azide bridges. The coordination shell is occupied by teaH2-, tea3-, six terminal N3 groups, six bridging azides (three 3N3 (N3, N23 and N42) and three 2N3 (N18, N26 and N30)), one methoxide (O32) and one methanol (O15) molecule (Fi gure 5-5a). The six br idging azides can be further divided into two groups: (Figure 5-5a).

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123 Layer A Layer C Layer BMn2 Mn8 Mn7 Mn16 O8 Mn4 Mn3 Mn1 N23 O10 O9 O4 O6 O1 O2 O7 Mn6 N26 Mn10 Mn9 O26 N18 O5 O27 O16 Mn5 O23 Mn11 Mn12 N30 O14 Mn18 Mn17 Mn14 Mn13 O19 O18 O17 O31 O22 O21 O30 O25 N42 O20 N33 Mn15Layer A Layer C Layer BMn2 Mn8 Mn7 Mn16 O8 Mn4 Mn3 Mn1 N23 O10 O9 O4 O6 O1 O2 O7 Mn6 N26 Mn10 Mn9 O26 N18 O5 O27 O16 Mn5 O23 Mn11 Mn12 N30 O14 Mn18 Mn17 Mn14 Mn13 O19 O18 O17 O31 O22 O21 O30 O25 N42 O20 N33 Mn15 Figure 5-6. A labeled ORTEP representation in PovRay format of the different layers of complex 13. MnIII green; MnII orange; O red; N blue; C gray, H have been omitted for clarity Table 5-4. Bond valence sum calculationsa for complex 13 Atom Mn2+ Mn3+ Mn4+ Mn(1) 3.118 2.893 2.971 Mn(2) 3.044 2.803 2.913 Mn(3) 2.917 2.681 2.793 Mn(4) 3.230 3.031 3.056 Mn(5) 3.166 2.934 3.017 Mn(6) 3.290 3.025 3.150 Mn(7) 3.173 2.927 3.032 Mn(8) 3.272 3.058 3.104 Mn(9) 3.182 2.922 3.049 Mn(10) 3.201 2.936 3.069 Mn(11) 2.903 2.678 2.775 Mn(12) 2.019 1.875 1.922 Mn(13) 3.118 2.903 2.965 Mn(14) 3.145 2.927 2.992 Mn(15) 3.210 2.997 3.047 Mn(16) 1.749 1.613 1.672 Mn(17) 3.102 2.850 2.971 Mn(18) 1.983 1.847 1.886 aThe underlined value is the one closest to the actual charge for which it was calculated. The oxidation state of a particular atom can be taken as the nearest whole number to the underlined value The metal oxidation states and the protonation levels of O2-, OH-, tea3-, and teaH2O atoms were established by Mn and O bond valence sum calculations (Table 5-4 and Table 5-5), inspection of metric parameters, and detection of MnIII Jahn-Teller (JT) elongation axes.

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124 Table 5-5. Bond valence sum calculations a for selected oxygen atoms in complex 13 Atom Vi Assignment O(3) 1.001 OHO(4) 1.969 O2O(5) 1.952 O2O(7) 1.001 OHO(8) 1.952 O2O(12) 1.104 OHO(15) 1.121 OHO(16) 1.873 O2O(17) 2.035 O2O(18) 1.760 O2O(19) 1.870 O2O(20) 1.782 O2O(21) 1.812 O2O(22) 1.802 O2O(28) 1.112 OHO(29) 1.090 OHaThe oxygen atoms is O2if Vi 2, OHif Vi 1, and H2O if Vi 0 5.3.2.4 Structure of [Mn31O20(N3)4(O2CMe)23(tea)2(dea)2(OMe)6(MeOH)2]n (14) The structure and metric parameters for [Mn31O20(N3)4(O2CMe)23(tea)2(dea)2(OMe)6(MeOH)2] (14) are presented in Figure 5-7 and Table A-13, respectively. Complex 14 can be described as Mn31 cluster units forming infinite chains that are further linked through azide bridges to produce infinite sheets in the ac plane. There are a total of twenty O2ions in the core of the structure; two 5-O2(O11, O73), twelve 4-O2(O2, O7, O16, O17, O25, O31, O51, O58, O67, O69, O71, O80) and six 3-O2(O12, O21, O30, O59, O68, O 74). There are six methoxides (O6, O34, O38, O47, O53, O78) and two methanol (O22, O27) molecules. Summarizing, the repeating unit (Figure 5-7) consists of eleven MnII and twenty MnIII ions, twenty oxides, two tea3-, two dea2-, and four azides. Amongs t the azides, one is 2-N3 and the remaining three are terminal. In fact, one of the terminal azides (N9/ N10/N11) is responsible for bridging the chains to form infi nite sheets as is shown in Figur e 5-8. Finally, to complete

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125 the peripheral ligation, there are twenty-three acetates. Eight of the acetates bridge in a rarer 1, 2, 3 mode, while the other fifteen bridge in their familiar 1, 1, ( syn , syn ) binding mode. Mn5 Mn11 Mn10 Mn13 Mn12 Mn14 Mn15 Mn16 Mn17 Mn28 Mn24 Mn25 Mn23 Mn20 Mn19 Mn18 Mn21 Mn30 Mn27 Mn26 Mn31 Mn4 Mn1 Mn9 Mn7 Mn6 Mn2 Mn3 Mn8 Mn22 Mn29 Mn5 Mn11 Mn10 Mn13 Mn12 Mn14 Mn15 Mn16 Mn17 Mn28 Mn24 Mn25 Mn23 Mn20 Mn19 Mn18 Mn21 Mn30 Mn27 Mn26 Mn31 Mn4 Mn1 Mn9 Mn7 Mn6 Mn2 Mn3 Mn8 Mn22 Mn29 Figure 5-7. An ORTEP representati on in PovRay format of the Mn31 repeating unit of complex 14. MnIII green; MnII orange; O red; N blue; C gray. H atoms have been omitted for clarity The metal oxidation states and the protonation levels of O2-, OH-, tea3-, and dea2O atoms were established by Mn and O bond va lence sum calculations (Tables 5-6 and 57), inspection of metric para meters, and detection of MnIII Jahn-Teller (JT) elongation axes. All Mn ions are hexa-coordina ted except six penta-coordinated MnIII ions (Mn1, Mn7, Mn13, Mn19, Mn24, Mn26) and two hepta-coordinated MnIII ions (Mn3, Mn25). The repeating unit of this complex is repating to both sides of the MnII (Mn16), there is a distorted cubane composed of two MnII (Mn10, Mn11/ Mn17, Mn18) and two MnIII (Mn12, Mn13/ Mn19, Mn20), two 3-O2and one 4-O2link to two further MnIII and one MnII, this layer links to a six MnIII and one MnII which have a binding between them through 2-O2-, 3-O2-and 4-O2(Figure 5-7).

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126 Table 5-6. Bond valence sum calculationsa for complex 14 Atom Mn2+ Mn3+ Mn4+ Mn(1) 3.154 2.885 3.029 Mn(2) 3.227 2.991 3.075 Mn(3) 1.963 1.813 1.875 Mn(4) 3.244 2.967 3.115 Mn(5) 3.072 2.810 2.863 Mn(6) 3.247 2.970 3.118 Mn(7) 2.968 2.715 2.850 Mn(8) 3.230 2.955 3.102 Mn(9) 1.995 1.825 1.916 Mn(10) 3.061 2.800 2.940 Mn(11) 1.887 1.726 1.812 Mn(12) 3.115 2.850 2.992 Mn(13) 3.042 2.782 2.921 Mn(14) 2.146 1.993 2.043 Mn(15) 2.107 1.957 2.006 Mn(16) 1.878 1.735 1.794 Mn(17) 1.847 1.689 1.773 Mn(18) 2.156 2.003 2.053 Mn(19) 3.171 2.901 3.045 Mn(20) 3.277 2.997 3.147 Mn(21) 1.902 1.739 1.826 Mn(22) 3.121 2.854 2.987 Mn(23) 1.968 1.801 1.890 Mn(24) 2.936 2.686 2.819 Mn(25) 1.940 1.793 1.852 Mn(26) 3.106 2.842 2.983 Mn(27) 2.980 2.726 2.862 Mn(28) 3.230 2.954 2.862 Mn(29) 3.224 2.949 3.096 Mn(30) 3.109 2.843 2.985 Mn(31) 3.101 2.875 2.956 aThe underlined value is the one closest to the actual charge for which it was calculated. The oxidation state of a particular atom can be taken as the nearest whole number to the underlined value Table 5-7. Bond valence sum calculationsa for selected oxygen atoms in complex 14 Atom Vi Assignment O(22) 1.243 OHO(57) 1.056 OHaThe oxygen atoms is O2if Vi 2, OHif Vi 1, and H2O if Vi 0

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127 The repeating unit is distorted along the Mn16 ion (MnII) with an angle of 93.01(5) (Figure 5-8). For a better understand ing of the structure, packing diagrams are shown in Figure 5-9. Figure 5-8. ORTEP representa tion in PovRay format show ing the bending of the Mn31 unit of complex 14. MnIII green; MnII orange; O red; N bl ue; C gray. H atoms have been omitted for clarity a) b) a) b) Figure 5-9. An stic k representation of 14 showing a) the packing diagram along the b axis, and b) the packing diagram along the c axis. MnIII green; MnII orange; O red; N blue; C gray. H atoms have been omitted for clarity. The view along the b axis (Figure 5-9a) allows us to identify the azides that link the chains to form sheets. Also, in the view along the c axis (Figure 5-9b) we can see the holes (empty spaces/channels) that are cr eated in the sheets formed by the Mn31

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128 polymeric units. Thus, this Mn31 polymer might behave as a multifunctional material with an amalgamation of interesting properties (such as gas absorption and magnetism). 5.3.3 Magnetochemistry of Complexes Variable-temperature magnetic susceptib ility measurements were performed on powdered polycrystalline samples of complexes 10 14, restrained in eicosane to prevent torquing, in a 0.1 T field and in the 5.0 -300 K temperature ranges. 5.3.3.1 Direct current magnetic studies of complexes 10-14 The magnetic behavior for complexes 10, 11 and 12 is observed to be the same, and for conciseness only complex 10 will be explained in detail. The results of the dc studies on the different complexes are shown as a MT vs. T plot in Figure 5-10. Temperature (K) 050100150200250300 MT (cm3 mol-1 K) 15 20 25 30 35 40 45 50 Complex 10 Complex 11 Complex 12 Figure 5-10. Plot of MT vs. temperature for a dried, mi crocrystalline sample of complex 10 in eicosane, measured in a 1.0 kG field The MT value at 300 K for complex 10 is 20.37 cm3 mol 1 K and reaches a maximum of 46.06 cm3 mol 1 K at 6.5 K. This behavior i ndicates a relatively large spin ground state ( S ) for 10. The MT value at 300 K expected for a cluster containing the MnII 4MnIII 3 formulation, with uncoupled spins and g = 2 is 26.5 cm3 mol 1 K. Due to the

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129 topological complexity of the molecule, it is not possible to determine the individual pairwise Mn2 exchange interactions using the Kamb Equivalent Operator method.52 H/T (kG/K) 024681012 M/N B 0 5 10 15 20 0.1 T 0.5 T 1 T 2 T fit Figure 5-11. Determination of ground stat e spin. Plot of reduced magnetization M / N B vs. H / T for a dried, microcrystal line sample of complex 10 in eicosane; the dc field value of each of the is ofield plots is indicated. Nevertheless, the spin of the ground state can be determined. For this, magnetization ( M ) measurements were performed in the 1.80-4.00 K temperature range and 0.1-3.0 T magnetic field range. The data is plotted as reduced magnetization ( M / NB) versus H / T (Figure 5-11), where N is Avogadro's number, B is the Bohr Magneton and H is the applied magnetic field. For a system occupying only the ground state and experiencing no zero-field splitting, the various isofield lines would be superimposed and M/NB would saturate at a value of gS . The non-superposition of the isofield lines in the Figure 5-11 is indicative of the presence of zer o-field splitting. The data were fit using a method described elsewhere54 that involves diagonalization of the spin Hamiltonian matrix, assuming only the ground state is occupi ed at these temperatures, and includes axial ZFS (D z 2), Zeeman interactions, and empl oys a full powder average of the magnetization. The best fits to the data (shown in Figure 5-11) were obtained with S = 10, g = 1.88, D = 0.05 cm 1 ( 0.07 K).

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130 Several heptanuclear Mn complexes ha ve previously been synthesized and characterized. A complex which was found to have the formulation MnII 4MnIII 3 is [Mn7(teaH)3(tea)3](ClO4)2, where teaH3 is triethanolamine.116b Magnetic susceptibility measurements reveal the ground state to be S = 11, and EPR measurements result in the observation of D = 0.08 cm 1 and a rhombic zero-field splitting parameter, E = 2.1 x 10 4 cm 1. Ac susceptibility shows thermally activ ated relaxation of the magnetization for temperatures above 1 K with an activation barrier of Ueff = 13.6 cm 1 (19.5 K) and a relaxation time of 0 10 8 s. The complex NEt4[Mn7(OH)3Cl3(hmp)9]Cl(MnCl4), a molecule also composed of MnII 4MnIII 3, possesses an S 10 ground state.124 [Mn7(OMe)12(dbm)6],125 is a complex made up of MnII 3MnIII 4 and possesses an S = 17/2 ground state. These complexes should exhibit hysteresi s below its blocking temperature, TB, in a magnetization versus dc field plot if they are SMMs. Previous experiments on similar Mn7 complexes show that these molecules have almost no field sweep rate dependence, and the hysteresis resulting is thought to come from the bulk-magnet behavior of the clusters, which results from weak intermolecu lar exchange interactions between them. Complex 13 has a MT value at 300 K of 52.70 cm3 mol 1 K and reaches a maximum of 60.76 cm3 mol 1 K at 90 K (Figure 5-12). Thereaft er, it decreases to a value of ~ 47-50 cm3 mol 1 K between the temperature ranges of 30 to 5 K. The MT value at 300 K expected for a cluster containing the MnII 3MnIII 15 formulation, with uncoupled spins and g = 2 is 58.12 cm3 mol 1 K. Additionally, the MT value at 5 K of 47 cm3 mol 1 K suggests a large ground state spin for the Mn18 complex, in the region of S = 21/2 1.

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131 Temperature (K) 050100150200250300 MT (cm3 mol-1 K) 20 30 40 50 60 70 Figure 5-12. Plot of MT vs. temperature for a dried, microcrystalline sample of complex 13 in eicosane, measured in a 1.0 kG field The dc magnetic susceptibility of complex 14 was studied in the 5.00-300 K range in a 1.0 kG applied dc field. The MT decreases steadily with decreasing temperature from 11.02 cm3mol-1 K at 300 K to 1.72 cm3mol-1K at 5 K, and is clearly heading for 0 Temperature (K) 050100150200250300 MT (cm3 mol-1 K) 2 4 6 8 10 12 02468 M'T (cm 3 mol -1 K) 0 1 2 3 Figure 5-13. Plot of MT vs. temperature for a dried, microcrystalline sample of complex 14 MeCN in eicosane, measured in a 1. 0 kG field. The inset plot is the inphase ac susceptibility, plotted as M T versus T cm3mol-1K at 0 K, indicating the presence of pr edominantly antiferromagnetic exchange interactions within the molecule and an S = 0 ground state spin for this complex. A further confirmation of the S = 0 ground state was sought by ac studies, the in-phase component of which is depicted in the inset plot of Figure 5-13. The M T value also

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132 clearly goes to zero at 0 K. Thus, the dc data in conjunction with th e ac studies confirm the S = 0 ground state of the Mn31 polymer. To confirm the ground state spin S , and to determine the magnitude of the zerofield splitting parameter D, magnetization vs. dc field meas urements were performed on samples of complex 13 restrained in eicosane, at applied magnetic fields and temperatures in the 1-9 kG (0.1-0.9 T) and 1. 8-2.5 K ranges, respectively. The data were H/ T (kG/K) 0123456 M/N B 0 2 4 6 8 10 12 14 16 0.1 T 0.2 T 0.3 T 0.4 T 0.5 T 0.6 T 0.7 T 0.8 T 0.9 T fit Figure 5-14. Determination of ground stat e spin. Plot of reduced magnetization M / N B vs. H / T for a dried, microcrystal line sample of complex 13 in eicosane; the dc field value of each of the is ofield plots is indicated fit to a model already explained pr eviously, using the program MAGNET,54 which fit the experimental data to those calculated using the above procedure for different values of S , D and g . The experimental data are plotted in Figure 5-14 as reduced magnetization ( M / N B) vs. H / T , where M (=MH ) is the molar magnetization, N is Avogadro’s number, B is the Bohr magneton, and H is the magnetic field. The fit of the data for complex 13 is shown as solid lines in Figure 5-14, and the fit parameters were S = 21/2, g = 1.81 and D = -0.06 cm-1 (-0.09 K). To ensure that the global fitting minimum had been obtained and to assess the precision in the obtained D and g parameters, root-mean-square fitting error surfaces

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133 were generated as a function of g and D, and those for complex 13 are shown in Figure 515 as a 2-D contour plots. These plots disp lay only the region of error space with negative D values; as is usually the case, accep table fits could also be found in both cases with positive D values, but the fits with nega tive D were clearly superior in the present cases. In addition, the results to be described later confirm that D is negative. As can be seen in Figure 5-15, there is only one erro r minimum in each of the fits, and these are relatively soft, the accuracy of these valu es is more difficult to assess, because magnetization fits are a good but not the best way to obtain accurate D and g values. Techniques such as EPR are much better for this purpose. g 1.651.701.751.801.851.901.952.00 D (cm-1) -0.1 0.0 0.1 0.2 0.3 0.0 0.5 1.0 1.5 2.0 2.5 3.0 1.65 1.70 1.75 1.80 1.85 1.90 1.95 2. -0.1 0.0 0.1 0.2 0.3e r r o rgD ( c m1 ) a) b) g 1.651.701.751.801.851.901.952.00 D (cm-1) -0.1 0.0 0.1 0.2 0.3 g 1.651.701.751.801.851.901.952.00 D (cm-1) -0.1 0.0 0.1 0.2 0.3 0.0 0.5 1.0 1.5 2.0 2.5 3.0 1.65 1.70 1.75 1.80 1.85 1.90 1.95 2. -0.1 0.0 0.1 0.2 0.3e r r o rgD ( c m1 ) a) b) Figure 5-15. Plots of the error surface for the error vs. D vs. g fit for complex 13. (a) two dimensional contour plot and (b) three dimensional mesh plot The values of the ground state spin and their associat ed significant magnetoanisotropy (D values) for complex 13 suggests that this complex might be a new single-molecule magnet (SMM). As stated in prev ious chapters, this requires a significant barrier ( U ) to magnetization relaxation (reorientation) , and the upper limit to this is given by ( S2-1/4) D for a half-integer spin system, or 6.6 cm-1 (9.5 K) for complex 13, using the magnetization fit parameters obtained earlie r. In fact, the true or effective barrier

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134 ( Ueff) is usually significantly smaller than U due to Quantum Tunneling of the Magnetization (QTM). We thus decided to investigate the magnetization dynamics of these complexes using ac magnetic susceptibility studies. 5.3.3.2 Alternating current magnet ic susceptibility studies Ac studies were performed in the 1.8-10 K range using a 3.5 G ac field oscillating at frequencies in the 25 – 1488 Hz range. The results for complex 10 are shown in Figure 5-16. Temperature (K) 024681012 M'' (cm3 mol-1) 0 1 2 3 4 997 Hz 250 Hz 50 Hz Temperature (K) 024681012 M' T (cm3 mol-1 K) 0 10 20 30 40 50 997 Hz 250 Hz 50 Hz b) a) Temperature (K) 024681012 M'' (cm3 mol-1) 0 1 2 3 4 997 Hz 250 Hz 50 Hz Temperature (K) 024681012 M' T (cm3 mol-1 K) 0 10 20 30 40 50 997 Hz 250 Hz 50 Hz b) a) Figure 5-16. Plot of the in-phase (a) (as M T ) and out-of-phase (b) (as M ) AC susceptibility signals vs. temperature fo r dried, microcrystalline sample of complex 10 in eicosane at the indicat ed oscillation frequencies The ground state S = 10 for 10 is not the maximum possible for a MnII 4MnIII 3 system, where we would expect S = 37/2 for the maximum spin possible. Extrapolation of M T to 0 K gives ~43-45 cm3mol-1K, which is below the consistent value for S = 10 and g ~ 1.9 of M T = 49.3 cm3mol-1K. The only problem of extrapolation to 0 K where only the ground state is populated can be the presence of w eak intermolecular exchange interactions. There is no fre quency-dependent out-of-phase M signal. The results for complex 13 are shown in Figure 5-17. For complex 13, the ac data in Figure 5-17a reveal several things: (i) the in-phase M T in Figure 5-17a is a plateau

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135 with decreasing temperature, and at ~ 8 K st arts decreasing with decreasing temperature; showing that at the lowest temperatures, th ere is a frequency-de pendent decrease in M T , concomitant with the appearance of a frequency-dependent out-of-phase M signal below 3 K. The peak of this signal is ev ident at frequency as low as 5 Hz; (ii) extrapolation of the M T value to 0 K gives 48.52 cm3 K mol-1, indicating an S = 21/2 ground state for the molecule. M T is given by g2S ( S +1)/8, so 48.65 cm3 K mol-1 gives S = 21/2 and g = 1.81, in excellent agreement with the result of the dc magnetization fit; (iv) there is a frequenc y-dependent decrease in M T at the lowest temperatures, with the decrease becoming apparent at higher temperat ures as the ac frequency increases; and (v) concomitant with (iv) there is a frequency-de pendent increase in the out-of-phase signal M , with only the tails visible above 1.8 K (the operating limit of our SQUID magnetometer) of peaks that clea rly lie at lower temperatures. Temperature (K) 024681012 M'T (cm3 mol-1 K) 35 40 45 50 50 Hz 25 Hz 10 Hz 5 Hz a) Temperature (K) 024681012 M'T (cm3 mol-1 K) 35 40 45 50 50 Hz 25 Hz 10 Hz 5 Hz a) Temperature (K) 024681012 M'' (cm3 mol-1) 0.0 0.1 0.2 0.3 50 Hz 25 Hz 10 Hz 5 Hz b) Temperature (K) 024681012 M'T (cm3 mol-1 K) 35 40 45 50 50 Hz 25 Hz 10 Hz 5 Hz a) Temperature (K) 024681012 M'T (cm3 mol-1 K) 35 40 45 50 50 Hz 25 Hz 10 Hz 5 Hz a) Temperature (K) 024681012 M'' (cm3 mol-1) 0.0 0.1 0.2 0.3 50 Hz 25 Hz 10 Hz 5 Hz b) Figure 5-17. Plot of the in-phase (a) (as M T ) and out-of-phase (b) (as M ) AC susceptibility signals vs. temperature fo r dried, microcrystalline sample of complex 13 in eicosane at the indicat ed oscillation frequencies The appearance of M'' signals in Figure 5-17b suggest s, but does not prove, that complex 13 is a single-molecule magnet. To confirm if 13 is indeed an SMM, studies of magnetization vs. dc field sweeps were necessa ry at temperatures < 1.8 K to see if

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136 magnetization hysteresis loops would be obtaine d, the diagnostic property of a magnet. These were carried out on single crystals at temperatures down to 0.04 K using a microSQUID apparatus and are described below.55 5.3.3.3 Magnetization vs. dc field hysteresis loops of 13 Shown in Figure 5-18 are the results of magnetization ( M ) vs. applied dc field scans for single crystals of 13CH2Cl2Et2O. In the figure are shown (i) the temperature dependence at a fixed sweep rate, and (ii) the field sweep rate dependence at a fixed temperature. Hysteresis loops are clearly ev ident below 0.8 K whose coercivity increases with decreasing temperature dow n to 0.04 K, as expected for the superparamagnet-like properties of a SMM (Figure 5-18a). The field sweep dependence at a constant temperature of 0.04 K in Figure 5-18b shows that the size of the step at zero field increases with decreasing sweep rate, as expected for a SMM from standard LandauZener theory, since the tunneling probability is inversely proportiona l to the sweep rate.35 -1 -0.5 0 0.5 1 -0.8-0.6-0.4-0.200.20.40.60.8 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K M/Ms 0H (T) 0.017 T/s -1 -0.5 0 0.5 1 -1-0.500.51 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s M/Ms 0H (T) 0.04 Ka) b) -1 -0.5 0 0.5 1 -0.8-0.6-0.4-0.200.20.40.60.8 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K M/Ms 0H (T) 0.017 T/s -1 -0.5 0 0.5 1 -1-0.500.51 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s M/Ms 0H (T) 0.04 Ka) b) Figure 5-18. Magnetization ( M ) vs. magnetic field hysteresis loops for a single crystal of complex 13CH2Cl2Et2O at (a) the indicated temp eratures and fixed sweep rate and (b) the indicated sweeping rate s at 0.04 K. M is normalized to its saturation value, Ms The loops do not exhibit the step-like feat ures indicative of QT M, but it is possible that steps are present but smeared out by broa dening effects from dipolar and transverse fields, low-lying excited states, and/or a distribution of molecular environments.

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137 In order to obtain the actual or effective barriers to magnetization relaxation ( Ueff), magnetization vs. time decay data were collect ed at temperatures down to 0.04 K. This gave a set of relaxation time ( ) vs. T data, which were used to construct an Arrhenius plot based on the Arrhenius re lationship of Eq. 5-5, where 0 is the pre-exponential term, Ueff is the (mean) effective barrier to relaxation, and k is the Boltzmann constant. These = 0 exp ( Ueff/k T ) (5-5) 0 0.1 0.2 0.3 0.4 0.5 0.11101001000M/Ms t (s)1 K 0.8 K 0.4 K 0.7 K 0.55 K 0.45 K 0.6 K 0.5 K 0.04 K 0.35 K 0.3 K 0.25 K 0.15 K 0.1 K 0.2 K 10-710-510-310-110110310510702468101214 (s) 1/T (1/K) a) b) 0 0.1 0.2 0.3 0.4 0.5 0.11101001000M/Ms t (s)1 K 0.8 K 0.4 K 0.7 K 0.55 K 0.45 K 0.6 K 0.5 K 0.04 K 0.35 K 0.3 K 0.25 K 0.15 K 0.1 K 0.2 K 10-710-510-310-110110310510702468101214 (s) 1/T (1/K) a) b) Figure 5-19. Relaxation time vs. temperat ure studies on a single crystal. (a) Magnetization vs. time decay plots at the indicated temperatures. (b) Arrhenius plot using the resulting relaxation time ( ) vs. T data for complex 13. The dotted line is a fit to the Arrhenius equation plots for complex 13 are presented in Figure 5-19. The fits of the thermally-activated region above 0.3 K, shown as the dashed line in Figure 5-19, gave Ueff/ k = 8.8 K. This effective barrier maybe compared to the potential energy barrier of U = 9.5 K obtained from magnetization fits. As already stated earlier, the U > Ueff for SMMs because of quantum tunneling of the magnetization th rough the anisotropy barrier. A further confirmation of QTM taking place in this Mn18 complex is obtained from the Arrhenius plot, which shows a temperature-independent region approximately below 0.15 K. Thus, at temperatures below 0.15 K, the relaxa tion time becomes essentially temperatureindependent at ~ 107 seconds, demonstrating ground state QTM. In this ground state

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138 quantum tunneling regime, tunneling now take s place only between the lowest lying MS sublevels of the S manifold, where S is the ground state spin of the Mn18 complex of 21/2. Thus, the Mn18 complex functions as a SMM and a dditionally displays QTM effects. 5.4 Conclusions The notion that the N,O,O-chelate and N,O, O,O-chelate are more flexible than the similar N,O,O-chelate pdm2(pdmH2 = pyridine-2,6-dimethanol), and might lead to distinctly different Mn complexes has turned out to be the case. Nmethyldiethanolamine (mdaH2) and triethanolamine (teaH3) in a mixed ligand strategy with azide groups, have proven to be a successful route to four new complexes of different nuclearities, all of them being mixed-valent MnIII/MnII species. Complexes 10, 11 and 12 are very similar to previous reported Mn7 complexes and the resulting structure and magnetic properties are also comparable. However, the Mn18 and Mn31 complexes are totally novel structur al types, with no precedence in the literature. Interestingly, a lthough both of these contain tr iethanolamine and azides, the magnetic properties are remarkably different with the ground state spin ranging from diamagnetic for Mn31 to the S = 21/2 for the Mn18 complex. Consequently, the Mn18 complex functions as a single-molecule ma gnet and displays hysteresis and quantum tunneling effects. Undoubtedly, the pr esence of end-on azides in the Mn18 complex acts as ferromagnetic trigger and stabilizes the high ground state spin for this complex. Thus, as a result of the mixed ligand stra tegy applied in this chapter, complexes 10-14 were isolated. These complexes are unusual and represent important new additions to polynuclear manganese complexes in zero, one and two dimensions. The obtainment of complexes of varying nuclearities from a singl e reaction system as demonstrated in this chapter, merely emphasizes how compli cated and unpredictable are the precise

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139 nuclearities and topologies of products of su ch labile and compli cated multi-component reactions. Nevertheless, these complexes pr ovide invaluable insights on the magnetic properties of molecular nanomagnets and contri bute to the development of this nascent field.

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140 CHAPTER 6 EXCHANGE-BIASED DIMER: OPTIMIZA TION OF THE MAGNETIC PROPERTIES AND FURTHER CHARACTERIZATION OF THE SYSTEM 6.1. Introduction Considerable effort has been devoted in the Christou group towards the study of families of tetranuclear manganese clusters,53,127 with the aim to understand and control the properties of SMMs. These tetranuclear sp ecies are the subject of investigation as they can be easily modified, and the magnetic data is much easier to interpret and model, than the data in larger clusters. Additiona lly, the change in magnetic properties arising from subtle structural or elec tronic variations can give a lead in the development of better SMMs. SMMs, by definition, are well isolated individual molecules, but the molecular properties that are required for a sufficie ntly large energy barrier to magnetization reversal do not preclude the presence of intermolecular interactions. At present, one of the most well-studied tetranuclear clusters, [Mn4O3Cl4(O2CEt)3(py)3] (here-after [Mn4]),18,128,129,130 displays intermolecular interactions of significant magn itude in the form of pairwise interactions and has been found to display slow relaxation of the magneti zation associated with an energy barrier of molecular origin. This SMM does not show any step at zero field in the hysteresis loops (unlike other SMMs), and it represents a nove l complex exhibiting exchange bias of all tunneling transitions due to weak interactions between two [Mn4] identical units. This system is called "exchange-biased SMMs" and re presents a useful subj ect for the study of the effects of intermolecular interactions on the behavior arising from the energy barrier

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141 to magnetization reversal. More importan tly, it has been suggested that such intermolecular interac tions may provide a means of fine -tuning the quantum tunneling of magnetization in SMMs. The deviation, in contrast to all SMMs (no tunneling at zero magnetic field), can be readily explained by weak antiferromagnetic (A F) exchange interactions between the two Mn4 subunits. The strength of this AF exchange coupling has been quantified from low temperature magnetic53 and EPR measurements.128 High-resolution inelastic neutron scattering (INS) studies on the Mn4 dimer are presented here. Previously, these INS studies had been successfully employed to accurately determine the anisotropy parameters in the ground state of several Mn4 SMM clusters.131 This study as presented in this chapter has two major objectives: i) to accurately determine the exchange splitting and thus the exchange paramete rs, and ii) to quantify the e ffect of deuteration of the hydrogen bonds on the coupling strength. Additionally, Park129 and coworkers had previously reported on a detailed electronic structure calc ulation of this system, using dens ity-functional theory (DFT), in order to explain the lack of a step at zero field. This theoretical study was done because Pederson had suggested129 that some of the spin-vibron interactions might play a role in the mechanism of magnetic quantum tunneling (MQT) in Mn12 acetate and related SMMs. For these reasons and to complement the DFT studies on the dimer, Raman and infrared measurements were performed which will also be discussed herein. This exchange-coupled dimer also shows quantum coherence with the superposition states remaining coherent fo r at least 1 nanosecond; the time needed to perform a single qubit operation.128 Hence this system has a massive impact on potential

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142 applications of SMMs as conventional memory storage devices or as qubits in future quantum computers. However, from a synthetic and physical chemist’s point of view, we need to explore and further fortify on this breakthrough. Also, the solvents of crystallization dramatically affect the quantum properties and the intra/inter dimer magnetic exchange interactions in these exchange-biased SMMs.18,128 For these reasons, a family of these dimers, [Mn4O3Cl4(O2CEt)3(py)3]4MeCN (15), [Mn4O3Cl4(O2CEt)3(d5py)3]4MeCN (16), [Mn4O3Cl4(O2CEt)3(py)3]C6H14 (17), [Mn4O3Cl4(O2CEt)3(py)3]x C6H12 (18) [Mn4O3Cl4(O2CEt)3(py)3]x C8H16 (19) and [Mn4O3Cl4(O2CEt)3(py)3]x oCl2C6H4 (20) have been synthesized. These will be discussed in detail, focusing on reducing environmental effects arising from solvent molecules to a minimal value, which are supposed to increase the intra-dimer magne tic exchange interactions (by bringing the two monomers closer) and to decrease the inter-dimer inte ractions (by separating the dimers from each other). 6.2 Experimental 6.2.1 Syntheses All manipulations were performed unde r anaerobic conditions using distilled solvents. All reagents were used as re ceived unless otherwise stated. Complexes [Mn3O(O2CMe)6(py)3](ClO4) and [Mn3O(O2CMe)6(d5-py)3](ClO4) were prepared as described elsewhere.28a,132 [Mn4O3Cl4(O2CEt)3(py)3]MeCN (15). To a solution of [Mn3O(O2CEt)6(py)3](ClO4) (1.90 g, 1.99 mmol) in distil led MeCN (50.0 mL) was added 0.50 mL of EtCOCl (5.75 mmol) drop-wise under a N2 atmosphere. After stirring for a few minutes, the solution was filtered and left in a water bath at 5 C overnight. The resulting black crystals were coll ected by filtration and stored under N2. The yield of

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143 complex 15 was 41%. Elemental analysis for [Mn4O3Cl4(O2CEt)3(py)3]2MeCN (C24H34N5Mn4O9Cl4): Experimental (calculated): C, 35.47; H, 3.83; N, 7.39. Found: C, 35.76; H, 3.76; N, 7.73 %. Selected FT-IR data (KBr, cm-1): 1608 (s), 1561 (s), 1487 (m), 1448 (s), 1398 (s), 1369 (s), 1289 (s), 1218 (m ), 1159 (w), 1071 (s), 1046 (m), 1017 (m), 918 (w), 890 (w), 811 (w), 767 (m), 694 (s), 651 (s), 586 (s), 508 (m), 437 (m). [Mn4O3Cl4(O2CEt)3(d5-py)3]MeCN (16). An analogous method to that described above was used in the synthesis of complex 16. To a solution of [Mn3O(O2CEt)6(d5-py)3](ClO4) (0.88 g, 1.00 mmol) in distilled MeCN (25.0 mL) was added 0.25 mL of EtCOCl (2.89 mmol) drop -wise. Following the same procedure as described for 15, black crystals were isolated by filtration. The yield of complex 16 was 39%. Elemental analysis for [Mn4O3Cl4(O2CEt)3(d5-py)3]MeCN (C26H33D5N4Mn4O18Cl4): Experimental (calculated): C, 29.71; H, 3.16; N, 5.33. Found: C, 29.95; H, 3.30; N, 5.48 %. Selected FT-IR data (KBr, cm-1): 1610 (s), 1562 (s), 1487 (m), 1449 (s), 1399 (s), 1371 (s), 1289 (s), 1216 (m), 1161 (w), 1073 (s), 1045 (m), 1016 (m), 918 (w), 891 (w), 811 (w), 768 (m), 694 (s), 651 (s), 589 (s), 510 (m), 435 (m). [Mn4O3Cl4(O2CEt)3(py)3]C6H14 (17). To a solution of [Mn3O(O2CEt)6(py)3](ClO4) (2.61 g, 2.73 mmol) in distilled CH2Cl2 (30.0 mL) was added 0.75 mL of EtCOCl (8.63 mmol) drop wise under a N2 atmosphere. The mixture was stirred for few minutes, filtered, and left at 5 C overnight. Later, the filtered mother liquor was layered with a mixture of Et2O/hexanes (1:1). After a couple of days black crystals were isolated by filtration. The yield of complex 17 was 44%. Elemental analysis for [Mn4O3Cl4(O2CEt)3(py)3]C6H14 (C30H44N3Mn4O9Cl4): Experimental (calculated): C, 37.84; H, 4.66; N, 4.41. Found: C, 37.51; H, 4.36; N, 4.70 %. Selected FT-IR data (KBr,

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144 cm-1): 1608 (s), 1561 (s), 1488 (m), 1448 (s), 1401 (s), 1369 (s), 1289 (s), 1218 (m), 1158 (w), 1071 (s), 1046 (m), 1017 (m), 917 (w), 890 (w), 811 (w), 767 (m), 694 (s), 651 (s), 586 (s), 508 (m), 440 (m). [Mn4O3Cl4(O2CEt)3(py)3]C6H12 (18). The synthesis was performed employing the same procedure used for 17. However, in this case, th e filtered mother liquor was layered with a mixture of Et2O/cyclohexane (1:1). After a couple of days black crystals were isolated by filtration. The yield of complex 18 was 39%. Elemental analysis for [Mn4O3Cl4(O2CEt)3(py)3]C6H12 (C30H42N3Mn4O9Cl4): Experimental (calculated): C, 37.92; H, 4.46; N, 4.42. Found: C, 37.63; H, 4.29; N, 4.51 %. Selected FT-IR data (KBr, cm-1): 1609 (s), 1563 (s), 1485 (m), 1448 (s), 1399 (s), 1369 (s), 1289 (s), 1219 (m), 1159 (w), 1072 (s), 1047 (m), 1017 (m), 916 (w), 892 (w), 812 (w), 765 (m), 694 (s), 651 (s), 586 (s), 509 (m), 438 (m). [Mn4O3Cl4(O2CEt)3(py)3]C8H16 (19). Complex 19 was synthesized using the procedure employed for 17. However, the filtered mother liquor was layered with a mixture of Et2O/cyclooctane (1:1). After a couple of days black crystals were isolated by filtration. The yield of complex 19 was 34%. Elemental analysis for [Mn4O3Cl4(O2CEt)3(py)3]C8H16 (C32H46N3Mn4O9Cl4): Experimental (calculated): C, 39.29; H, 4.74; N, 4.30. Found: C, 38.99; H, 4.54; N, 4.62 %. Selected FT-IR data (KBr, cm-1): 1608 (s), 1561 (s), 1487 (m), 1448 (s), 1399 (s), 1369 (s), 1289 (s), 1218 (m), 1159 (w), 1068 (s), 1050 (m), 1015 (m), 920 (w), 889 (w), 811 (w), 767 (m), 694 (s), 651 (s), 586 (s), 508 (m), 437 (m). [Mn4O3Cl4(O2CEt)3(py)3]o-Cl2C6H4 (20). Complex 19 was also synthesized in an analogous way to complex 17. In the follow up, the filtered mother liquor was layered

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145 with a mixture of Et2O/o-dichlorobenzene (1:1). After a couple of days black crystals were isolated by filtration. The yield of complex 20 was 46%. Elemental analysis for [Mn4O3Cl4(O2CEt)3(py)3]o-Cl2C6H4 (C30H34N3Mn4O9Cl6): Experimental (calculated): C, 38.24; H, 3.64; N, 4.46. Found: C, 38.38; H, 3.36; N, 4.75 %. Selected FT-IR data (KBr, cm-1): 1612 (s), 1565 (s), 1485 (m), 1446 (s), 1402 (s), 1372 (s), 1295 (s), 1215 (m), 1162 (w), 1069 (s), 1049 (m), 1020 (m), 922 (w), 892 (w), 814 (w), 770 (m), 698 (s), 653 (s), 587 (s), 512 (m), 439 (m). 6.2.2 X-ray Crystallography The crystallographic charac terization of complexes 15, 16 and 17 were only performed. Since complexes 18, 19 and 20 are variations in the solvent of crystallization, the crystal structures were not solved. Instead, the products we re analyzed and identified by IR spectroscopic comparison and Elemental An alysis (vide supra). Data for the crystal structures were collected at 173 K on a Siemens SMART PLATFORM equipped with a CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Absorption corrections by integration were applied based on measured indexed crystal faces. The structures were solved by the Direct Methods in SHELXTL5, and refined using full-matrix least squares. Th e non-H atoms were treated anisotropically, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. Refinement was done using F2. For complex 154MeCN, cell parameters were refined using up to 8192 reflections. A full sphere of data (1381 frames) was collected using the -scan method (0.3 frame width). The first 50 frames we re re-measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). The asymmetric

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146 unit consists of 1/3 of the Mn4 cluster and 11/3 molecules of MeCN. Thus the ratio of the cluster to MeCN is 1:4. The MeCN in gene ral position is disorder ed over two positions and was refined in two parts. Their site oc cupation factors were dependently refined to 0.921 for the major part, and consequently 0.081 for the minor part. The MeCN on the three-fold axis was also disordered and refine d in two parts. One part located exactly on the 3-fold rotation axis and was given a 1/6 instead of 1/3. The other part was located just outside of the rotation ax is and was also given a 1/6 occupation factor. A total of 192 parameters were refined in the final cycle of refinement using 2010 reflections with I > 2(I) to yield R1 and wR2 of 5.74% and 12.25%, respectively. For complex 16MeCN, the asymmetric unit consists of one third of the Mn cluster, a MeCN in general position and a MeCN molecule sitting on a 3-fold rotation symmetry element. Thus the ratio of cl uster-to-MeCN is 1-to-4. A total of 171 parameters were refined in the final cycle of refinement using 1751 reflections with I > 2(I) to yield R1 and wR2 of 3.91% and 10.30%, respectively. For complex 17C6H14, the asymmetric unit consists of 1/3 Mn4 cluster and a 1/3 of a hexane molecule. The latter was disordered ov er a three-fold rotation axis and could not be resolved. Thus program SQUEEZE,32 a part of the PLATON33 package of crystallographic software, was used to calcula te the solvent disorder area and remove its contribution to the overall intensity data. A to tal of 134 parameters were refined in the final cycle of refinement us ing 2662 reflections with I > 2(I) to yield R1 and wR2 of 3.34% and 11.53%, respectively.

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147 6.3 Results and Discussion 6.3.1 Syntheses The syntheses of [Mn4O3Cl4(O2CR)3(py)3] [Mn4] complexes involves a trinuclear manganese source, [Mn3O(O2CR)6(py)3](ClO4)28a,133 as starting materials; there are often used to form high nuclearity Mn/O/RCO2 aggregates.134 These complexes can be synthesized in a variet y of ways. One approach135 involves treating a solution of these trinuclear complexes with 5.5 equivalents of Me3SiCl. In the present work, complexes 15-20 were synthesized us ing a solution of the trinuclear manganese source and adding 3.5 e quivalents of EtCOCl in dry or distilled solvents135 (MeCN, CH2Cl2, o-Cl2C6H10) under anaerobic conditions. This caused the formation of a red-brown solution. Complex 16 ([Mn4O3Cl4(O2CEt)3(d5-py)3]4MeCN) was prepared in an analogous manner to 15 ([Mn4O3Cl4(O2CEt)3(py)3]MeCN) using [Mn3O(O2CEt)6(d5-py)3](ClO4) as starting material. After 24 hours at 5 C, small black crystals were obtained from the soluti on. In order to synthesize complexes 17-19, [Mn4O3Cl4(O2CEt)3(py)3]x solvent, distilled CH2Cl2 was used, followed by layering with ether/solvent (1:1). However, complex 20 was synthesized using o-dichlorobenzene as a solvent of reaction as well as solvent of crystallization. The preparation of complexes 15-20 is summarized in Eq. 6-1. 5 [Mn3O(O2CEt)6(py/d5-py)3](ClO4) + 15 EtCOCl + 4 H2O 3 [Mn4O3Cl4(O2CEt)3(py/d5-py)3] + 15 (EtCO)2O + 3 Mn2+ + 6 Hpy+(O2CEt)+ 2H+ + 3Cl(6-1)

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148 The presence of EtCOCl is required due to the otherwise possi ble reaction of the produced acid anydride (i.e., (EtCO)2O) with adventitious water molecules liberating free acid (i.e., EtCO2H), which would exchange with c oordinated carboxylate ligands in the final complexes 15-20. Thus, EtCOCl acts as a "carboxylat e abstractor" in these reactions in which 3MnIII ions present in the "triangle" st arting material are converted to 3MnIII, 1MnIV ions which form the "cubane" product. 6.3.2 Description of Structures There is crystallographic data available only for the complexes 15, 16 and 17, which consequently will prove crucial to understanding and comparing the experimental results obtained on compexes 18, 19 and 20. Table 6-1. Crystallographic data for complex 15, complex 16 and complex 17 Parameter 15MeCN 16MeCN 17C6H14 formulaa C72H136Mn12N10O44 C58H90Cl4Mn4N4O18 C143H138Mn6N2O24 fw, g mol-1 948.19 1066.25 942.18 space group R 3 R 3 R 3 a , 16.103(2) 16.0465(8) 16.3676(6) b , 16.103(2) 16.0465(8) 16.3676(6) c , 28.357(4) 28.219(2) 27.981(2) , deg 90 90 90 , deg 90 90 90 , deg 120 120 120 V , 3 6362(2) 6292.7(6) 6491.7(5) Z 6 6 18 T , K 193(2) 193(2) 193(2) mm-1 1.471 1.489 1.461 radiation, b 0.71073 0.71073 0.71073 calc, g cm-3 1.612 1.631 1.461 R 1 ( wR 2) %c , d 5.74 (12.25) 3.91 (10.30) 3.34 (11.53) a Including solvent molecules. b Graphite monochromator. c R 1 = || Fo| – | Fc|| / | Fo|. d wR 2 = [w ( Fo 2 Fc 2)2] / [ w Fo 2)2]]1/2 where S = [[ w ( Fo 2 – Fc 2)2] / ( n p )]1/2, w = 1/[2( Fo 2) + ( m * p )2 + n * p ], p = [max( Fo 2, 0) + 2* Fc 2]/3, and m and n are constants

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149 Crystallographic data for complexes, [Mn4O3Cl4(O2CEt)3(py)3]4MeCN (15), [Mn4O3Cl4(O2CEt)3(d5-py)3]4MeCN (16), and [Mn4O3Cl4(O2CEt)3(py)3]C6H14 (17) are presented in Table 6-1. As the effects of these dimer arrangeme nts on the magnetic properties of these compounds is clearly manifested in the hyste resis studies, the hyste resis studies have been performed in detail on each of these dimers in order to understand the magnetic properties. 6.3.2.1 Structure of [Mn4O3Cl4(O2CEt)3(py)3]MeCN (15) Complex 15 can be described as a Mn4 pyramid with a central [Mn4( 3-O)( 3Cl)]6+ core and with idealized C3v symmetry. The MnIV ion is located at the apex and coordinated by 3-O atoms to the three MnIII ions situated on the base of the pyramid. A 3-Cl atom bridges to this basal plane, and each MnIII ions displays Jahn-Teller distortions manifested as elongations along the axes containing the Cl atom. All the Mn O3 O2 O1 N1 Mn2 Mn1 Cl2 Cl1 O3 Cl2 Mn2 Mn1 O2 O1 Cl1 N1 O3 O2 O1 N1 Mn2 Mn1 Cl2 Cl1 O3 Cl2 Mn2 Mn1 O2 O1 Cl1 N1 Figure 6-1. ORTEP repr esentation of complex 15, [Mn4O3Cl4(O2CEt)3(py)3]. MnIII light purple; MnIV purple; O red; N bl ue; C gray. Solvent molecules and hydrogen atoms have been omitted for clarity

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150 ions have distorted c oordination geometries; MnIV is coordinated to six O atoms. On the other hand, each of the three MnIII ions are coordinated to four O atoms, one Cl atom, and one pyridine N atom. The ratio between the Mn4 cluster and the solv ent is 1 to 4. Two independent MeCN solvent molecules were loca ted in the asymmetric unit, one lying in a general position, the other sitting on the 3-fold axis. Two different views of the structure of [Mn4O3Cl4(O2CEt)3(py)3] (15) are shown in Figure 6-1, and selected metric parameters are listed in Tabl e A-14. Further studies of the crystallographic data have shown that pairs of Mn4 molecules ([Mn4]2) are lying head-tohead on a crystallographic S6 symmetry axis (Figure 6-2). Figure 6-2. ORTEP representation of the [Mn4]2 dimer of [Mn4O3Cl4(O2CEt)3(py)3]. MnIII light purple; MnIV purple; O red; N blue; C gray, H lightgray. Solvent molecules have been omitted for clarity . The blue dashed lines are C-HCl hydrogen bonds and the green dashed lin e is the close ClCl interaction They are creating a total of seven inte rmolecular interactions: six C-HCl hydrogen bonds between the pyridine rings on one Mn4 molecule and Cl ions on the

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151 other, at 3.706 with an angle of 158.0, a nd a ClCl interaction of the central bridging chloride ions of each Mn4 within the dimer. The later distance, (ClCl) = 3.858 , is very close to the Van der Waals separation of the chloride ions (3.6 ) In addition, hydrogen bonds between neighboring dimers have been observed. These C-HO interactions occur between the O from the core of a Mn4 unit interacting with the meta -H from the pyridine ring on an adjacent dimer. Packing diagrams are shown in Figure 6-3. In a dimer, each Mn4 is surrounded by a total of three adjacent Mn4, from neighboring dimers, having a total of 6 interactions. Sele cted interatomic distances and angles for complex 15 are presented in Table 6-2. 90 90 Figure 6-3. ORTEP representation of two dimers. The box is to emphasize the intermolecular interactions between the two dimmer clusters. And ORTEP representation afte r 90 rotation. MnIII light purple; MnIV purple; O red; N blue; C gray, H light gray. Solvent molecules have been omitted for clarity. The brown dashed lines are C-HO hydrogen bonds and the green dashed line is the close ClCl interaction. The small black arrows point the intermolecular intera ctions between the oxygen from one molecule and the CH from the pyridine molecule of the neighbor

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152 6.3.2.2 Structure of [Mn4O3Cl4(O2CEt)3(d5-py)3]MeCN (16) Complex 16 is isostructural to complex 15. Selected distances and angles for complex 16 are depicted in Table A-15. This complex crystallizes in the space group R 3 with an identical intermolecular arrangement to 15 generating pairs of dimers. The deuterated pyridine molecules in this structure modify the intermolecular interactions between the Mn4 units of the dimer, and at the same time the communication between adjacent dimers, as shown in Table 6-2. As for complex 16, this complex contains a total of four molecules of solvent per Mn4 in the unit cell. Due to the similarities between complexes 15 and 16, only ORTEP figures of 15 are shown. 6.3.2.3 Structure of [Mn4O3Cl4(O2CEt)3(py)3]C6H14 (17) Complex 17 is isostructural with complexes 15 and 16. Table A-16 shows the selected distances and angles of this comp lex. The main difference between complexes 17 and 16 is the solvent in which the molecules were crystallized. For 17, the asymmetric unit consists of 1/3 Mn4 cluster and 1/3 of a hexane molecule of crystallization. Table 6-2. Comparison of selected interm olecular distances () and angles () for complexes [Mn4O3Cl4(O2CEt)3(py)3] , where 15MeCN, 16MeCN and 17C6H14 Parameters 15 16 17 Space group R 3 R 3 R 3 ClCla 3.878(12) 3.712(10) 3.844(7) ClCb 3.706 3.664 3.721 C-HClb 158.00 151.94 157.36 COc 3.290 3.296 3.345 C-HOc 170.13 167.94 165.69 J cm-1/K -0.07/-0.10 -0.10/-0.15 -0.07/-0.10 a Intermolecular distance () between (3-Cl) ions. bIntermolecular distance () and angle () between C and m -H from pyridine and the 2-Cl ion within the dimer. c Intermolecular distance () and angle () between bridging oxide and C and m -H from pyridine between different dimers (int eractions between adjacent dimers)

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153 A comparison of selected interatomic distances and angles for complexes 15-17 is presented in Table 6-2. As can be observed, complex 15 displays interactions with its nearest neighbors, but the ethyl group provides a greater se paration between the dimers, when compared to [Mn4O3Cl4(O2CMe)3(py)3]. Complex 17, with hexane as a solvent of crystallization, displays stronger exchange in teractions within the dimer arrangement, and the hysteresis measurements confirm the better isolation of each [Mn4]2 from the surroundings,128 a fact already observed by crystallography. Complex 16, [Mn4O3Cl4(O2CEt)3(d5-py)3], is similar to the non-deuter ated complex and comparison of the hysteresis data shows very small variations , being in the range of experimental error. From these results, we can confirm that the intermolecular interactions play a very important role in determining the magnitude of the magnetic exchange interactions in the dimer, and in the next section, we will be ab le to relate the magnetic results to hysteresis studies, and see how the structure is related to the properties observed. 6.3.3 Magnetization studies 6.3.3.1 Magnetization studies for complexes 1520 Complexes 18, 19 and 20 have variations in only the solvent molecules of crystallization. Additionally, previous studies on complexes 15-17,135 had confirmed that they have similar magnetic behavior. Thus, the magnetism of only complexes 18-20 will be explained in more detail in this section, with slight references to the magnetism of complexes 15-17 for the sake of comparison. Variable-temperature magnetic susceptib ility measurements were performed on polycrystalline samples of complexes 15-20, restrained in eicosane to prevent torquing, in a 10 kG applied magnetic field in the 5.0300.0 K range. Figure 6-4 shows a plot of MT vs. temperature for all the complexes, i.e., 15-20.

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154 The value of MT for complex 18 is 9.55 cm3 mol-1 K at 300 K; this is slightly lower than the spin-only value of 10.88 cm3 mol-1 K expected for a system containing three MnIII and one MnIV non-interacting ions. At lower temperatures, MT slowly increases to a maximum of 10.86 cm3 mol-1 K at 80.0 K, thereafter dropping to a value of 6.39 cm3 mol-1 K at 5.0 K due to Zeeman effect s, and intermolecular interactions. Temperature (K) 050100150200250300 M T (cm 3 mol -1 K) 4 6 8 10 12 14 complex 15 complex 16 complex 17 complex 18 complex 19 complex 20 Figure 6-4. Plot of MT vs. temperature for dried, microc rystalline samples of complexes 15-20 in eicosane, measured in a 10 kG field. For complex 19, MT at 300 K is 9.31 cm3 mol-1 K, reaching a maximum of 10.95 cm3 mol-1 K at 60.0 K. At lower temperatures, MT drops to 6.74 cm3 mol-1 K at 5.0 K. Similarly, the MT values for complex 20 increase from 10.01 cm3 mol-1 K at 300 K to 11.85 cm3 mol-1 K, at 50.0 K, respectively. Later, the value decrease to 9.44 cm3 mol-1 K at 5.0 K. In order to describe the nature of the superexchange magnetic coupling within these four distorted trigon al pyramidal manganese clusters with C3v symmetry, the magnetic susceptibility data were fit to the appropriate M vs. T theoretical equation, given by the

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155 Van Vleck equation.57 The complete equation for these species is shown in the Appendix D-2.Using the appropriate Heisenberg excha nge Hamiltonian, a suitable spin-eigenvalue equation (Eq. 6-1) was found for these [Mn4(3-O)3(3Cl)(O2CEt)3(py)3] complexes. = 4 1 3 1 2 1 34 4 3 4 2 3 2 33 2 2 S S S S S S J S S S S S S J (6-1) where iS refers to the spin of the manganese atom Mni, and J33 and J34 are the exchange parameters for the coupling between MnIII and MnIII and between MnIII and MnIV ions, respectively. The Hamiltonian in Eq. 6-1 was transformed into an equivalent form (Eq. 6-2) by applying the Kamb v ector coupling method52 and the substitutions A = 2 + 3 + 4, and T = 1 + A, where T is the resultant spin of the complete molecule. = 2 2 1 2 34 2 4 2 3 2 2 2 33 A AS S S J S S S S JT (6-2) From Equation 6-4 we can obtain the energy expression (Eq. 6-3). 1 1 1 ,34 33 A A T T A A A TS S S S J S S J S S E (6-3) The eigenvalue expression and the corresponding Van Vleck equation57 were then used to least-squares-fit the experimental data measured in the 1.8-300 K range. Data below 60 K for complexes 15-20 were not included in the fi tting due to the presence of intermolecular interactions and Zeeman effect which are likely to dominate in this temperature range. The parameters that we re varied during this procedure were J33, J34 and g, with a fixed temperature-indepe ndent paramagnetism (T IP) value of 600-6 cm3 mol-1. As the crystallographic data shows, the cores of this group of [Mn4(3-O)3(3Cl)]6+ complexes 15-17 are essentially super-imposable, and together with the fact that the magnetic exchange pathways occur mainly through the three 3-O and the one 3-Cl,

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156 and assuming that the rest of complexes 18-20 are essentially as complexes 15-17, the use of the above model is reasonable for the six complexes under study. The values of g, J33 and J34 determined from these fits are given in Table 6-3. Temperature (K) 050100150200250300 M T (cm 3 mol -1 K) 6 7 8 9 10 11 12 13 Complex 15 Complex 16 Complex 17 Complex 18 Complex 19 Complex 20 fitting Figure 6-5.Plots of MT vs. temperature for a dried, micr ocrystalline sample of complexes 15-20 in eicosane. M is the dc molar magnetic susceptibility measured in a 10 kG field. The solid lines are the fit of the data to the theoretical equation; see the text for the fit parameters Table 6-3. Parameters obtained from fitting the 10 kG susceptibility data of [Mn4O3Cl4(O2CEt)3(py/ d5-py)3] (complexes 15-20) Parameters 15 16 17 18 19 20 g 1.94 2.01 1.93 1.95 1.91 2.03 ST 9/2 9/2 9/2 9/2 9/2 9/2 J33 (cm-1) 10.3 12.4 12.9 13.0 12.8 10.4 J34 (cm-1) -31.4 -34.9 -33.3 -32.6 -33.2 -34.8 Dc magnetization vs. field measurements we re carried out in order to investigate the magnetic field dependence of the magnetizati on of all three complexes, to confirm the ground spin state, and to determine the magnit ude of the zero-field splitting parameter. Figures 6-6 show the reduced magnetization ( M / NB) plots for complexes 18-20 collected at 30, 40, 50, 60 and 70 kG, in the range of 1.8 to 10 K, where M is the magnetization, N is Avogradro’s number, B is the Bohr magneton, and H is the magnetic field. For complexes populating only the ground state and with no zerofield splitting, the

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157 magnetization follows the Brillouin function an d the isofield lines all superimpose and saturate at a plateau value of g S , at high fields and low temper atures. In all the plots, the isofield lines are not superimposed, indicating that the ground state is zero-field split. The reduced magnetization at 70 kG in all four complexes appear s close to saturation at the lowest temperatures with an M / NB of around 9, the theoreti cal saturation value for systems with a S = 9/2 ground state and g = 2. In addition, the separation between the isofield lines is related to S = 9/2 and to D, the axial anisotropy parameter. H/T (kG/K) 510152025303540 M/N B 6.5 7.0 7.5 8.0 8.5 3 T 4 T 5 T 6 T 7 T fitting H/T (kG/K) 5101520253035 M/N B 6.5 7.0 7.5 8.0 8.5 3 T 4 T 5 T 6 T fitting a) b) c) H/T (kG/K) 5101520253035 M/N B 7.5 8.0 8.5 9.0 3 T 4 T 5 T 6 T fitting H/T (kG/K) 510152025303540 M/N B 6.5 7.0 7.5 8.0 8.5 3 T 4 T 5 T 6 T 7 T fitting H/T (kG/K) 5101520253035 M/N B 6.5 7.0 7.5 8.0 8.5 3 T 4 T 5 T 6 T fitting a) b) c) H/T (kG/K) 5101520253035 M/N B 7.5 8.0 8.5 9.0 3 T 4 T 5 T 6 T fitting Figure 6-6. Determination of ground stat e spin. Plot of reduced magnetization M / N B vs. H / T for a dried, microcrystalline sample of complexes 18 (a), 19 (b) and 20 (c) in eicosane; the dc field value of eac h of the isofield plots is indicated The experimental data were fit to a th eoretical equation a ssuming that only the ground state is populated in the 1.8-10 K te mperature range. The parameters obtained

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158 from fitting the experimental data are presented in Table 6-4. All four complexes are very similar, showing only small variations in the values of g and D. Table 6-4. Parameters obtained from fitting the 10 kG susceptibility data of [Mn4O3Cl4(O2CEt)3(py/ d5-py)3] (complexes 15-20) Parameters 15 16 17 18 19 20 g 1.94 2.01 1.93 1.95 1.91 2.03 ST 9/2 9/2 9/2 9/2 9/2 9/2 D (cm-1) -0.54 -0.50 -0.55 -0.63 -0.63 -0.62 The magnetization vs. dc field hyste resis measurements for complexes 15-20 were performed on a micro-SQUID apparatus and th e resulting hysteresis loops are presented in the next section. 6.3.3.2 Magnetization vs. dc field hysteresis loops for complex 15 From previous work, hysteresis data for complex 15MeCN, was measured on a micro-SQUID apparatus55 and hysteresis loops were observe d at temperatures below 1 K, confirming this complex to be an SMM below this temperature. Figure 6-7 depicts hysteresis loops of compound 15 at a constant scan rate of 0.14 T/s, at a range of temperatures from 1.0 K to 0.04 K and also at a constant temperature (0.04 K) at a variety of scan rate (0.004-0.140 T/s), respectively. -1 -0.5 0 0.5 1 -1.2-0.8-0.400.40.81.2 0.04 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 1.0 K M/Ms 0H (T) 0.14 T/s -1 -0.5 0 0.5 1 -1.2-0.8-0.400.40.81.2 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s M/Ms 0H (T) 0.04 Ka) b) -1 -0.5 0 0.5 1 -1.2-0.8-0.400.40.81.2 0.04 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 1.0 K M/Ms 0H (T) 0.14 T/s -1 -0.5 0 0.5 1 -1.2-0.8-0.400.40.81.2 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s M/Ms 0H (T) 0.04 Ka) b) Figure 6-7. a) Hysteres is loops measured along Hz in the presence of a constant transverse field varying the temperature from 1.0 K to 0.04 K. b) Hysteresis loops measured along Hz in the presence of a constant temperature varying the scan rate from 0.140 T/s to 0.004 T/s

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159 At that time, this was the first SMM w ith two unique features observed in the hysteresis measurements of complex 15. The first is the absence of a quantum tunneling of magnetization step at zero field. Secondl y, the positions of the observed steps are irregular, displaying unique a ppearance. For these reasons, a theoretical model taking into account this unique phenomenon was postulated which agreed with the experimental behavior, and has been explained elsewhere.18 The antiferromagnetic nature of all seven intermolecular interactions within the [Mn4]2 unit (six C-HCl and one ClCl pathwa ys) is a result of the delocalization of the spin density from d orbitals of the MnIII ions into the pyridine -system and overlap with Cl -orbitals,136 and even more important, by th e approach of the central Clions of each Mn4 cluster in the dimer; propagation of exchange interactions through metal-bound Clions is well documented.137 The values of D and J used to calculate the energy diagram were obtained from the field positions of the steps in the hysteresis loops, ignoring transverse (and fourth or der) terms (Figure 6-8). -1.5 -1 -0.5 0 0.5 1 -1.2-0.8-0.400.40.81.2 M/Ms 0H (T) x1x2 Figure 6-8. Hysteresis loops measured along Hz at a temperature of 0.04 K and a scan rate of 0.140 T/s

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160 The zero-field splitting parameters and the intermolecular exchange interaction were calculated as described below by Eq. 6-4 and Eq. 6-5, respectively. 1x k g DB B (6-4) 2x k g JB B (6-5) The positions were determined from th e first derivative plots (Figure 6-9b). -1 -0.5 0 0.5 1 -1.2-0.8-0.400.40.81.2 0.140 T/s 0.017 T/s 0.004 T/s M/Ms 0H (T) 0.04 K 0 2 4 6 8 10 -0.400.40.81.2 0.140 T/s 0.035 T/s 0.004 T/s dM/dH 0H (T) (1) (2)(3) (4)(5)a) b) -1 -0.5 0 0.5 1 -1.2-0.8-0.400.40.81.2 0.140 T/s 0.017 T/s 0.004 T/s M/Ms 0H (T) 0.04 K 0 2 4 6 8 10 -0.400.40.81.2 0.140 T/s 0.035 T/s 0.004 T/s dM/dH 0H (T) (1) (2)(3) (4)(5)a) b) Figure 6-9. a) Hysteres is loops measured along Hz from -1.2 T to 1.2 T at a temperature of 0.04 K and 0.004, 0.017 and 0.140 T/s scan rates. b) Derivative plot of the hysteresis loop at 0.04 K and at different field sweep rates. Dashed lines and numbers indicate the dominating tunnel transitions The calculated values for complex 15 are D = -0.72 K /-0.50 cm-1 and J = -0.1 K /0.07 cm-1. The former is very close to that determ ined experimentally for several isolated distorted cubanes138 and to the values obtained from the measurements of the direct current magnetization vs. magnetic field for this particular complex. The latter is antiferromagnetic and very weak, as expected from the nature of the interactions. As Figure 6-8 shows, the exchange interaction between the two molecules in the dimer is related to the distance of the first quantum tunneling transi tion from zero field; the further

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161 this transition occurs from zero field, the stronger the interaction between the clusters become. The fitting of the data of the hysteresis loops allowed the quantification of the exchange parameter J between the two units in the dime r and also the zero-field splitting parameter, D, was easily established by the stu dy of the step separart ion in the hysteresis (Figures 6-8, 6-9). But, additional minor steps were observed for this complex studying the derivative of the magnetization. This fine structure of the steps has to be considered as these steps are related to the interaction of each [Mn4]2 with other dimers. Thus, an important goal of this project was to reduce the fine structure of the steps which would occur from increasing the intermolecular in teractions within the dimer (intradimer interaction) and also isolating it form its environment (such as reducing interdimer interactions by bulky solvent molecules etc.). 6.3.3.3 Magnetization vs. dc field hysteresis loops for complex 16 Identical studies were carried out on the deuterated version of compound 15. The goal of such experiments was to measure va riations in the hydrogen bond interactions arising between the terminal chloride atoms from a cluster with the pyridine ring of the adjacent in the dimmer. Thus, a comparison of the obtained exchange parameters could be made between the H containing cluster (15) and the deuterium containing complex (16). Hysteresis loops at different temperatur es and scan rates were obtained on a single crystal of complex 16. However, the variations obtained by comparison of this data with that obtained for compound 15 were very small, being in the range of experimental error. 6.3.3.4 Magnetization vs. dc field hysteresis loops for complex 17 Complex 17 is isostructural with complexes 15 and 16, all having the ground state S = 9/2. So far, the comparison of 15, 16 has allowed the study of possible variations in

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162 the exchange interactions within [Mn4]2 dimers and between adjacent arrangements through changing the nature of the carboxylat e ligand or the pyridine molecules. Now, the main difference between 17 and 15 resides in the crystallization solvent, compound 17 containing one molecule of hexane when compared to the four molecules of MeCN found in the case of 15. Typical hysteresis loops at a cons tant scan rate were performed as shown in Figure 6-10. -1 -0.5 0 0.5 1 -1-0.500.51 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 0.9 K 1.0 K M/Ms 0H (T) NA11 0.580 T/s Figure 6-10. Hysteresis loops of complex 17, [Mn4O3Cl4(O2CEt)3(py)3]C6H14 at a scan rate of 0.580 T/s and a variety of temperatures in the range 0.04-1.0 K The hysteresis loops were observed at temperatures below 1.0 K, at which 17 behaves as a SMM. However, two main featur es distinguish this complex from the one previously studied in this chapter. First of all, comparison with the previous complex 15 reveals that this compound di splays stronger exchange interactions within the dimer arrangement. This is calculated by sweeping the field from negative to positive values and considering the distance from the first qua ntum tunneling process from 0 T. The first quantum tunneling transition was observed at -0.48 T. The fitting of the experimental data gave J = -0.15 K /-0.10 cm-1 and D = -0.80 K /-0.55 cm-1. Hysteresis loops of complexes 15 and 17 at 0.04 K and at a scan rate 0.08 T/s are depicted in Figure 6-11. A

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163 comparison of the plots reveals that complex 17 show the stronger intradimer exchange interaction (the first step is farther away from 0 T for 17). o H (T) -1.5-1.0-0.50.00.51.01.5 M/Ms -1.0 -0.5 0.0 0.5 1.0 Complex 15 Complex 17 Figure 6-11. Hysteresis loops at 0.04 K and 0.008 T/s of complex 15 [Mn4O3Cl4(O2CEt)3(py)3]MeCN (blue) and 17 [Mn4O3Cl4(O2CEt)3(py)3]C6H14 (green) -1 -0.5 0 0.5 1 -1-0.500.51 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s M/Ms 0H (T) NA11 0.04 K 0 1 2 3 4 5 -1-0.500.51 0.008 T/s 0.017 T/s 0.035 T/s 0.070 T/s 0.140 T/s dM/dH 0H (T) NA11 0.04 K a) b) -1 -0.5 0 0.5 1 -1-0.500.51 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s M/Ms 0H (T) NA11 0.04 K 0 1 2 3 4 5 -1-0.500.51 0.008 T/s 0.017 T/s 0.035 T/s 0.070 T/s 0.140 T/s dM/dH 0H (T) NA11 0.04 K a) b) Figure 6-12. a) Hysteresis loops of 17 at 0.04 K and variable scan rates. b) derivative plot in identical conditions Another interesting observation is the absence of fine structure in the resonances, not having minor steps at any ranges of temperat ure or scan rate. Studies of the derivate of magnetization vs. the magnetic field di splay well defined peaks for the quantum tunneling transitions that occur between -1.2 T and 1.2 T, confirming the absence of fine structure in the resonances and conse quently the better isolation of each [Mn4]2 from the surroundings, a fact already obs erved from crystallography.

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164 6.3.3.5 Magnetization vs. dc field hysteresis loops for complexes 18, 20 Complexes 18 and 20 have the same hysteresis loops and only the hysteresis loops for complex 18 will be shown in Figure 6-13 at a constant scan rate of 0.14 T/s, at a range of temperatures from 1.0 K to 0.04 K and also at a constant temperature (0.04 K) at a variety of scan rate (0.004-0.140 T/s), respectively. Also, complex 20 with similar hysteresis to complex 18 is shown in Figure 6-14. -1 -0.5 0 0.5 1 -1-0.500.51 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 1 K M/Ms 0H (T) 0.14 T/s -1 -0.5 0 0.5 1 -1-0.500.51 0.280 T/s 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s M/Ms 0H (T) 0.04 Ka) b) -1 -0.5 0 0.5 1 -1-0.500.51 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 1 K M/Ms 0H (T) 0.14 T/s -1 -0.5 0 0.5 1 -1-0.500.51 0.280 T/s 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s M/Ms 0H (T) 0.04 Ka) b) Figure 6-13. a) Hysteresis loops for 18 measured along Hz in the presence of a constant transverse field varying the temperature from 1.0 K to 0.04 K. b) Hysteresis loops measured along Hz in the presence of a constant temperature varying the scan rate from 0.280 T/s to 0.001 T/s -1 -0.5 0 0.5 1 -1-0.500.51 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 1.0 K M/Ms 0H (T) 0.14 T/s -1 -0.5 0 0.5 1 -1-0.500.51 0.560 T/s 0.280 T/s 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s M/Ms 0H (T) 0.04 Ka) b) -1 -0.5 0 0.5 1 -1-0.500.51 0.04 K 0.2 K 0.3 K 0.4 K 0.5 K 0.6 K 0.7 K 0.8 K 1.0 K M/Ms 0H (T) 0.14 T/s -1 -0.5 0 0.5 1 -1-0.500.51 0.560 T/s 0.280 T/s 0.140 T/s 0.070 T/s 0.035 T/s 0.017 T/s 0.008 T/s 0.004 T/s 0.002 T/s 0.001 T/s M/Ms 0H (T) 0.04 Ka) b) Figure 6-14. a) Hysteresis loops for 20 measured along Hz in the presence of a constant transverse field varying the temperature from 1.0 K to 0.04 K. b) Hysteresis loops measured along Hz in the presence of a constant temperature varying the scan rate from 0.560 T/s to 0.001 T/s

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165 A comparison of hysteresis loops of compounds 15, 17, 18 and 20 at 0.04 K temperature and at a scan rate 0.04 T/s is depicted in Figure 6-15, where complexes 18 and 20 show the same strongest exchange interaction. o H (T) -1.5-1.0-0.50.00.51.01.5 M/Ms -1.0 -0.5 0.0 0.5 1.0 Complex 15 Complex 17 Complex 18 Complex 20 Figure 6-15. A comparison of the hysteresis loops at 0.04 K and 0.004 T/s of complexes 15 [Mn4O3Cl4(O2CEt)3(py)3]MeCN (blue); 17 [Mn4O3Cl4(O2CEt)3(py)3]C6H14 (green); 18 [Mn4O3Cl4(O2CEt)3(py)3]C6H12 (black) and 20 [Mn4O3Cl4(O2CEt)3(py)3]o-Cl2C6H4 (red) The main difference between 15, 17, 18 and 20 resides in the crystallization solvent. Complexes 15, 17, 18 and 20 contain four molecules of MeCN, one molecule hexane, one molecule of cyclohexane, and o-di chlorobenzene, respec tively. An important feature is that all the variations of these co mplexes do not have the st ep at zero field. The calculated values for complexes 18 and 20 are approx`imately D = -0.91 K /-0.63 cm-1, and J = -0.17 K /-0.12 cm-1. We can observe the strongest exchange interaction in complexes 18 and 20, as indicated by magnetic su sceptibility measurements.

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166 6.4 Inelastic Neutron Scattering Spectroscopy To obtain a larger ground state spin S a nd/or a more negative anisotropy D, it is crucial to better understand th e effects of chemical and physical variations on these magnetic parameters. Consequently, we have undertaken an inelastic neutron scattering (INS) study of these two (complexes 15 and 16) Mn4 derivatives. In such systems, INS is a powerful tool to obtain detailed magnetic information including magnetic anisotropy parameters (axial, rhombic, and upto the fourth order) as it does not rely on an applied magnetic field. Previous experi ments on other molecular magnets139 have shown that the anisotropy parameters can be derived with great accuracy. 6.4.1 Experimental Section For both experiments, the samples, [Mn4O3Cl4(O2CEt)3(py)3] (15) and [Mn4O3Cl4(O2CEt)3(d5-py)3] (16) were freshly prepared as described previously, and were checked by X-ray powder diffraction, elemental analysis and variable temperature dc magnetization measurements. 6.4.2 Results and Discussion The Mn4 subunits consist of one Mn4+ ( S = 3/2) and three Mn3+ ( S = 2) ions, which form a distorted cubane stru cture as depicted in Figure 6-1. Dominant AF exchange coupling between the Mn4+ ion and each of the Mn3+ ions in the subuni t leads to a wellisolated total spin S = 9/2 ground state for each Mn4 subunit. Jahn-Teller distortions of the Mn3+ ions introduce an easy-axis type magnetic anisotropy along the trigonal axis of the cluster.140 The S = 9/2 ground state is thus split into five MS Kramers doublets. This splitting can be described by the effec tive zero-field splitting Hamiltonian 0 4 0 4 3 1 2 z ZFSO B ) 1 S ( S S D H (6-6)

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167 where ) 1 S ( S 6 S 25 S ) 1 S ( S 30 S 35 O 2 z 2 z 4 z 0 4 . The leading term is the D term, with a negative D value of the order of D -0.06 meV for all the known Mn4 SMMs.138,139b The resulting splitting pattern is shown in Figure 6-16a. In the title compound two identical Mn4 molecules are lying head-to-head on a crystallographic S6 axis. In terms of anisotropy the two subunits are thus equivalent and represented by the same parameters in Eq . 6-6. A small perturbation is introduced by the exchange coupling between the two subun its, leading to the following effective Hamiltonian for the dimer B A B , ZFS A , ZFSS S J H H H , (6-7) where , ZFSH are centered on the two s ubunits A and B, respectively and have the form of Eq. 6-6. The effect of a positive (antiferroma gnetic) J value on the ground state splitting is seen in Figure 6-16b. All the Kramers doublets of the Mn4 subunits are split into two or three components. In first order, the dime r wavefunctions are gi ven by the symmetric 2 M , M M , M M , MA S B S B S A S s B S A S and antisymmetric 2 M , M M , M M , MA S B S B S A S a B S A S linear combinations of the basis functions, withB S A S SM M M . INS transitions are allowed for MS = 1. In the first order description, this corresponds specifically to 1 MA S and 0 MB S or 0 MA S and 1 MB S . The experimentally assigned allowed transi tions within the energy level diagram of Figure 6-16b are shown as arro ws and labeled I through VI.

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168 Figure 6-16. Energy level diagram of: (a) an axially anisotropy split S = 9/2 ground state (Eq. 6-6 with D = -0.063 meV and 0 4B = -6.810-6 meV) of a Mn4 subunit and (b) a [Mn4]2 dimer with antiferromagnetic coupling (Eq. 6-7 with D = -0.063 meV, 0 4B = -6.810-6 meV and J = 0.0073 meV). For clarity only the relevant states are shown. The arrows in b) correspond to the assignments of observed transitions in Figures 6-17 and 6-18. The approximate wavefunctions are given for 0 MA S in the following notation Based on their temperature dependence, th e major peaks in the INS spectra of Figures 6-17 and 6-18 can be assigned to the allowed transitions I to VI from Figure 616b. From the resulting energy-splitting pattern the relevant parameters in Eq. 6-7 can be determined approximately. Figure 6-17 shows the INS spectra after background subtraction of the complex 15 at 6.1 K and 19.4 K measured on the direct ge ometry time-of-flight spectrometer IN5 at the ILL, both on the energy gain (Figure 617a) and energy loss (Fi gure 6-17b) side. The

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169 complex 15 was also measured on IRIS at 1.5 K, 3.2 K and 19.2 K (not shown). The data are very similar to those of complex 16 (Figure 6-18, vide infra). Figure 6-17. INS spectra at 6.1 K and 19.4 K of complex 15, polycrystalline sample recorded on IN5 with an initial wavelength i = 7.0 after background subtraction: a) energy gain side, b) energy loss side. The labeling of the peaks corresponds to Figure 6-16. The solid lin es represent the simulated spectra with the following parameters: D = -0.0629(5) meV, 0 4B = -6.8(4)-6 meV, J = 0.0073(4) meV, FWHM = 0.031 meV (loss-side) and FWHM = 0.05 meV (gain-side) Figure 6-18 shows the IN S spectra of complex 16 at 1.5 K, 3.2 K and 19.2 K, measured on the inverted geometry time-of-fli ght spectrometer IRIS at the ISIS Facility. The solid lines in Figure 6-18a represent a smooth background that accounts for finite instrumental resolution as well as elastic a nd quasielastic scattering from the sample not associated with magnetic INS transitions. Th e neutron energy loss side of the spectra after background subtraction is shown in Figure 6-18.

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170 Figure 6-18. (a) INS spectra at 1.5 K, 3.2 K and 19.2 K of polycrystalline sample of complex 16, recorded on IRIS w ith a final wavelength f = 6.6 . The spectra correspond to the sum of all scattering angles. The solid lin e represents the background. (b) The INS spectra shown in (a) after background subtraction. The labeling of the peaks corresponds to Figure 6-16 . The solid lines represent the simulated spectra, with the following parameters: D = -0.0626(5) meV, 0 4B = -6.8(4)-6 meV, J = 0.0072(4) meV and FWHM = 0.035 meV At 1.5 K one strong peak (I) at 0.56 meV and two weaker features (III, IV) at lower energies are observed. The intens ity of peak (I) is almost cons tant as a function of Q. The Q dependence is most likely smeared out due to the high hydrogen content of the sample. At elevated temperatures the intensity of the cold peak (I) decreases , and several partially resolved hot peaks at lower energies are observed. Peak (I) broadens with increasing temperature, and the maximum slightly shifts to lower energy. This indicates that peak (I) is composed of several transitions at elevat ed temperatures. Since some of the observed peaks consist of more than one transition, we included the relative intensities of the INS transitions in addition to their energies for a more accurate determination. The INS cross

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171 section for a transition m n ( n and m denote eigenstates of the Hamiltonian (Eq. 6-7) is proportional to the th ermal population of the initial level n and the transition strength Inm(Q) (or Inm(Q) for a polycrystalline sample), where Q = k k’ is the momentum transfer with k and k’ defined as the initial and final wavevectors, respectively. In the calculation of Inm(Q) the geometry of the cl uster enters via the socalled interference factors.141 Since the [Mn4]2 cluster is describe d magnetically by an effective dimer model, see Eq. 6-7, a simple application of the INS cross section formula would miss important interference effects, and yield incorrect IN S intensities. The interference effects, howev er, can be retained in the dimer model as described in ref. 142, and for a polycrystalline sa mple of the uniaxial (Mn4)2 dimer Inm(Q) is obtained as B , A z z ij y y x x ij nmS ~ S ~ ) , Q ( g S ~ S ~ S ~ S ~ ) , Q ( f 3 2 ) Q ( I R R (6-8) with ij ij 2 2 0 ij 0 j * i ij) QR ( j ) ( C 2 1 ) QR ( j F F 16 1 ) , Q ( fijR R and ij ij 2 2 0 ij 0 j * i ij) QR ( j ) ( C ) QR ( j F F 16 1 ) , Q ( gijR R and n S m m S n S ~ S ~ u v u v , where and index the subunits A and B and i, j the individual Mn ions in the cluster, respectively. Fi(Q) is the magnetic form factor of the ith ion, jk is the spherical Bessel function of order k, Rij = Ri-Rj is the distance vector between the ith and jth ion, 2 / 1 ) R R ( 3 ) ( C2 ij ij,z 2 0 ijR and , = x, y, z. Based on Eq. 6-8 a least-squares fit of the calculated INS spectra, assuming Gaussian lineshapes, to the experimental da ta at all the measured temperatures, was

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172 performed. The results are shown as solid li nes in Figures 6-17 and 6-18 for the complex 15 and 16 samples, respectively. The agreement of the simulated and observed spectra is excellent for both samples at all temperatur es. The parameters obt ained are shown in Table 6-5. Within the experimental accuracy there is no significant difference between the two parameter sets. Table 6-5. Spin Hamiltonian parameters for the deuterated (complex 16) and undeuterated dimer (complex 15) Complex D (meV) 0 4B(meV) J (meV) 15 0.0629(5)/0.7304(5) 6.8(4)10-6 0.0073(4) 16 0.0626(5)/0.0727(5) 6.8(4)10-6 0.0072(4) An interesting question is whether the exchange interacti on between the two subunits is isotropic or not.128 In first order, the effect of the Jxy components of the exchange coupling is to split the two levels s2 9 , 2 7 and a2 9 , 2 7 by 9Jxy. All the other energy splittings of the Kramers doublets result from the Jz component of the exchange interaction. Since the Jxy component affects such a small portion of the spectrum, the introduction of exchange anis otropy does not significantly improve a leastsquare fit to the whole spect rum. However, from the ener gy difference between transition II and III, which is related to the splitting of the a , s2 9 , 2 7 levels, Jxy can be directly determined. Transition III is nicely resolved at 3.2 K, whereas transition II lies in the lower energy tail of peak (I). This can be s een in the broadening and slight shift of the maximum of peak I to lower energy with incr easing temperature. Peak (III) has an energy of 0.463(5) meV and the energy of transition II is estimated to 0.530(15) meV. Their energy difference of 0.065(20) meV corresponds to Jxy = 0.007(2) meV. Within experimental accuracy there is no difference to the isotropic J value of 0.0072(4) meV, indicating isotropic exchange.

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173 According to X-ray diffraction, the geometries of the Mn4 subunits in the complex 15 and 16 are not distinguishable. But the ClCl separation of the two subunits is slightly different: ClCl distances of 3.844(3) and 3.878(4) at 173 K for the crystals 15 and 16, respectively. We thus intuitively exp ect a stronger exchange coupling in the deuterated sample. The INS data analysis allows J to be determined within an accuracy of 5%. Since no significant differe nce for the two samples is found, we conclude that the increase of J upon deuteration is at most 5%. The samples used in the present study contained 8 molecules of acetonitrile per [Mn4]2 dimer in the crystal structure. This was the solvent used for the crystallization. This sample was studied in great detail by very low temperature magnetic measurements,53 and a value of J = 0.0086 meV was derived from these, somewhat larger than the J value obtained by INS. The spectroscopic value is considered more reliable, because it results from a direct observation of energy splittings. An EPR study of the same (Mn4)2 dimer was performed on a sample containing 2 molecules of n-hexane, instead of acetoni trile, as solvent of crystallization.128 A J value of Jhexane = 0.103(9) meV was determined for this sa mple. This is significantly larger than the value Jacetonitrile = 0.073(4) meV obtained in the pres ent study. Inspection of the crystal structures shows a significant shortening of the ClCl separation in the EPR sample: dClCl = 3.712(2) versus dClCl = 3.86 for the average of the INS samples. The difference between the two samples cont aining different solvent molecules is significantly larger than the difference between the deuterat ed and undeuterated versions of the title compound. And we observe th e intuitively expected trend: stronger

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174 antiferromagnetic exchange for the sample with the shorter ClCl distance. The relevant numbers are collected in Table 6-6. Table 6-6. ClCl distances and J values for the three different [Mn4]2 samples samplea ClCl () Jmagn b (meV) JINS (meV) JEPR c (meV) 15 3.878(4) 0.0086 0.0073(4) 16 3.844(3) 0.0072(4) 17 3.712(2) 0.103(9) a15: [Mn4O3Cl4(O2CEt)3(py)3]28MeCN (undeuterated); 16: [Mn4O3Cl4(O2CEt)3(pyd5)3]2MeCN (deuterated); 17: [Mn4O3Cl4(O2CEt)3(py)3]2C6H14; b from ref. 18; c from ref. 128 This is a very interesting result because it demonstrates that the distance between the two subunits in the [Mn4]2 dimer, and thus the strength of the exchange coupling between the subunits, is more strongly aff ected by exchanging the solvent molecules situated between the [Mn4]2 dimers in the crystal struct ure, than by deuterating the CHCl hydrogen bonds connecting the Mn4 subunits within the dimers. The effect of the solvent exchange on the ClCl distance is a bout five times as large as the effect of deuteration. And the antiferromagnetic J value is about 40% larger in the sample with nhexane solvent molecules. In the theory of kinetic exchange the antiferromagnetic J value is related to one-electron transfer integral, wh ich, in turn, are related to orbital overlap integrals. For two approaching s ubunits, the distance dependence of J at long distances is given by e-kd, where d is the distance between the subunits.66,129 Taking the ClCl distance as d and the spectroscopically determined J values in Table 6-6, a value of k = 2.5(9) is obtained . This is in reasonable agreement with the result of a recent DFT calculation on the title compound which derived k = 4.5.129 The fact that solvent exchange has a str onger effect on both structure and exchange coupling than deuteration, is a reflection of the intrinsi c weakness of the C-HCl hydrogen bonds. Despite this weakness, the si x C-HCl bonds manage to structurally

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175 join together the two Mn4 subunits in the title compound.144 And they may well play an important part as pathways for th e small superexchange between the Mn4 subunits. 6.5. Raman Studies Pederson had suggested that some of the sp in-vibron interactions might play a role in the mechanism of MQT in Mn12 acetate and related SMMs.145 For these reasons and to complement previous studies by Park,129 where they reported a detailed electronic structure calculation of this system, Raman and infrared measurements (IR) were performed on complex 15, and are reported here. Figure 6-19 shows a typical Ra man spectrum of the SMM [Mn4]2. Numerous strong peaks can be seen below 1600 cm-1. As discussed by theory129b most of the vibrational data can be anal yzed roughly within the harm onic-oscillator approximation by using the monomer as a model, and replacing the ethyl group (-CH2CH3) by H. There are a total of 3N = 3 56 = 168 degrees of freedom, si x of which are translational and rotational modes. All the others were considered vibrationally stable. Assignment of the peaks observed experimentally for [Mn4]2, in cm-1, in the Raman spectra, will be made using the DFT calculations results. The obs erved Raman peaks can be broadly group together in four groups (Table 6-7). Due to the large size of [Mn4]2, there is a collective beha vior of the vibrational modes, and thus a breakdown of the trad itional selection rule s for Raman and IR spectroscopy. We have therefor e utilized the ‘‘functional gr oup’’ approach for the mode assignment even though the vibrational mode s in SMMs, especially the lowest-energy ones, are collective, and involve the entire molecule. One significant advantage of the functional group analysis is that the vibr ations can be easily visualized and are appropriate for describing the motion of ligands.

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176 Raman shift (cm-1) 4008001200 1600Intensity (arb. units) 1017 608 537 509 219 Raman shift (cm-1) 4008001200 1600Intensity (arb. units) 1017 608 537 509 219 Raman shift (cm-1) 4008001200 1600Intensity (arb. units) 1017 608 537 509 219 Figure 6-19. The Raman modes of complex 15 Table 6-7. Assignment of Raman modes (cm-1) for complex 15 following the DFT calculations results Raman modes for [Mn4]2 DFT calculations Assignment 192, 219, 274 194, 212, 278 Metal-ligand vibrations not involving O2316, 354, 382, 409, 443, 509, 537, 608 301, 361, 380, 423, 444, 514, 543, 602 Mn-O vibrations 647, 1017, 1075, 1222, 1541, 1570, 1609 640, 1019, 1066, 1207, 1547, 1563, 1604 Pyridine vibrations 1044, 1399, 1541, 1570, 1609 1547b, 1563b, 1604b -O2CEt a a Known from the literature. b Modes that contain contributions from –O2CEt and pyridine Taking this experimental a pproach, one way to identify the vibrational modes of the dimer, complex 15, is to study a set of model compounds, which were used in order to provide additional insight into the peak assignments, Mn-O bond in MnO2, KMnO4, and Mn(O2CMe)2 were studied (Table 6-8, Figure 6-20).

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177 Intensity (arb. units)Raman Shift (cm-1) MnO2Mn(O2CMe)2[Mn4]2 316 406 1044 1410 KMnO46001200 1800 Intensity (arb. units)Raman Shift (cm-1) MnO2Mn(O2CMe)2[Mn4]2 316 406 1044 1410 KMnO46001200 1800 Figure 6-20. Comparison of the Raman sp ectra of model compounds to that of [Mn4]2 at 295 K Table 6-8. Assignment of Raman modes (cm-1) for [Mn4]2 following the experimental approach Raman modes (cm-1) for [Mn4]2 Mode assignment (cm-1) Model compounds 192, 274 196, 281 MnCl2 (not shown) 316 317 MnO2 409 406 KMnO4 1399, 1570, 1609 1410, 1572, 1615 Mn(O2CMe)2 The Raman spectrum of the model compound MnCl2, which contains two peaks at 196 and 281 cm-1 was compared to the [Mn4]2 data, due to the similarity of position and intensity, to the modes observed at 192 and 274 cm-1 in [Mn4]2 and these peaks are thus assigned to Mn-Cl vibrations. Additionally, they will be compared later to other complexes with Mn-Cl vibrations (vide infra). The mode at 316 cm-1 in the SMM, also present in the model compound MnO2 at 317 cm-1, is due to a Mn-O vibration. The strong peak at 406 cm-1 in KMnO4, which is also attributed to Mn-O, matches very well with the mode observed at 409 cm-1 in [Mn4]2. Small broad peaks at 1399, 1570, and 1609 cm-1

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178 correspond to the peaks seen in Mn(O2CMe)2 at 1410, 1572, and 1615 cm-1, which leads to their assignment as relating to Mn-O-R vibrations. From literature, the peak observed at 1044 cm-1 in the Raman spectrum is a ssigned to a vibration in O2CEt.146 The modes occurring at 1160 and 1609 cm-1 are related to vibrations in the pyridine rings.146 Another way to identify the vibr ational modes of the dimer [Mn4]2 is to study related monomers, Mn4-Pr and Mn4-Ac. Hence, these were compared to the spectrum of [Mn4]2 as seen in Figure 6-21, and Table 6-9. Although the ligand structure is different, the core structure remains identical to that of [Mn4]2. Intensity (arb. units)Raman Shift (cm-1) 600 1200 1800 Mn4-Pr Mn4-Ac [Mn4]2 1598 1017 1322 1491 Intensity (arb. units)Raman Shift (cm-1) 600 1200 1800 Mn4-Pr Mn4-Ac [Mn4]2 1598 1017 1322 1491 Figure 6-21. Spectral comparison of the monomers Mn4-Pr and Mn4-Ac with that of the dimer [Mn4]2. Note the absence from the [Mn4]2 spectrum of the three ligand vibrations observed in the monomers around 1322, 1491, 1598 cm-1. These are thus assigned to -Pr (O2CEt) and -Ac (O2CMe) moieties (see text) Several of the peaks in the spectra of Mn4-Pr and Mn4-Ac are very similar in both position and magnitude to modes observed in [Mn4]2.

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179 Table 6-9. Assignment of Raman modes (cm-1) for [Mn4]2 following the experimental approach Raman modes (cm-1) for [Mn4]2 Mode assignment (cm-1) Model compounds 192 194 Mn4-Pr 192 191 Mn4-Ac 1017, 1044 1000, 1029 Mn4-Pr 1017, 1044 1002, 1027 Mn4-Ac 1322, 1491, 1598 -(O2CEt) and -(O2CMe) The small peak observed at 192 cm-1, attributed to a Mn-Cl vi bration, is evident in both Mn4-Pr and Mn4-Ac, at 194 and 191 cm-1, respectively. Because the monomers only contain Mn-Cl in the core c ubane, the vibration at 192 cm-1 in [Mn4]2 must be related to Mn-Cl vibrations in the cubane structure. Furthermore, the absence of a Mn-Cl peak at 274 cm-1 in the monomers, implies this mode in [Mn4]2 is related to vibrations in the three Mn-Cl bonds on the periph ery of the cubane structur e. The intense modes which appear at 1000 and 1029 cm-1 in Mn4-Pr and 1002 and 1027 cm-1 in Mn4-Ac are slightly shifted from analogous p eaks seen at 1017 and 1044 cm-1 in [Mn4]2. Although there are many similarities at low frequencies in the spectra of the monomers as compared to the spectrum of the dimer, there are also severa l striking differences at higher frequencies. This is due to the fact the core cubane vibr ations occur at lower frequencies, while the ligand modes appear at a higher range. The most evident of these differences is the absence of the three intense peaks which are observed in the monomers at 1322, 1491, and 1598 cm-1. These vibrations are attributed to the ligands on the monomers which are significantly different than those attached to the dimer. It should also be noted that in the frequency range studied, there do not app ear to be any modes which are related specifically to any intermolecular coupling in [Mn4]2. Finally, the IR spectrum of the dimer, along with it’s comparison with the Raman spectrum is displayed in Fi gure 6-22. Also, a comparison between the vibrations (cm-1)

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180 obtained from IR, Raman, and DFT calculations are presented in Table 6-10. As can be seen in Table 6-10, the values from thes e three independent st udies are satisfyingly consistent with each other.129b 3416 2980 2841 435 1016608Intensity (arb. units) Wavenumbers(cm-1) 1000 2000 3000 4000 3416 2980 2841 435 1016608Intensity (arb. units) Wavenumbers(cm-1) 1000 2000 3000 4000 IR RamanIntensity (arb. units)400 800 1200 1600 Mn-O Mn-O2CEt pyridine Wavenumber(cm-1) IR RamanIntensity (arb. units)400 800 1200 1600 Mn-O Mn-O2CEt pyridine Wavenumber(cm-1) Figure 6-22. Typical IR spectrum of the SMM [Mn4]2. (b) A comparison of Raman and IR spectra Table 6-10. Assignment of Raman and IR modes (cm-1) for [Mn4]2 predicted by DFT calculations Raman modes for [Mn4]2 IR modes for [Mn4]2 DFT calculations Assignments 443 438 444 Mn-O2CEtb 509 508 514 Mn-Ob 537 539 543 Mn-Oa 608 608 602 Mn-Oa 647 649 640 Pyridinea , b 694 671 Pyridinea 767 745 O2CH, pyridinea 918 920 Mn-Ob, pyridinea 1017 1016 1019 Pyridinea 1075 1073 1066 Pyridinea 1222 1221 1207 Pyridinea 1450 1439 Pyridinea 1488 1472 Pyridinea 1541 1547 1547 -O2CEt, a , b pyridine, a, b Mn-O-Ra , b 1570 1565 1563 -O2CEt, a , b pyridine, a, b Mn-O-Ra , b 1609 1608 1604 -O2CEt, a , b pyridine, a, b Mn-O-Ra , b 2941 2942 Assymetric C-Ha , b 2980 Assymetric C-H a , b 3416 background a modes assigned by theory b modes assigned by experiment

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181 According to the IR spectr um, a mode related to O2and Mn, which is calculated to appear at 543 cm-1, is evident in the IR spectrum at 539 cm-1. The peak that is predicted at 1563 cm-1 in the theoretical calculations occurs at 1565 cm-1 in the IR. This mode is assigned to vibrations in the O2CEt and the pyridine rings.146 Peaks observed in the experimental spectrum at 694 and 1161 cm-1, but not predicted by the DFT calculations, are related to pyridine ring vibratio ns. The mode which appears at 2941 cm-1 in the IR, and is predicted at 2942 cm-1, is attributed to sy mmetric C-H vibrations. 146 Additionally, the unpredicted peak at 2980 cm-1 is also attributed to an asymmetric C-H vibration.146 It should be noted many of the modes in the IR spectrum also appear in the Raman data. For example, the peak observed at 647 cm-1 in the Raman spectrum is also present in the IR at 649 cm-1. The sharp peak at 1609 cm-1 in the Raman is observed in the IR at 1608 cm-1, and is predicted by the theory at 1604 cm-1. 6.6 Conclusions In this chapter we have discussed a family of dimers in which each member contains a [Mn4] lying facing towards an identical [Mn4] system forming dimers, [Mn4]2. A total of six hydrogen bonds between chlo rine atoms and pyridine ring from the peripheral ligands and also possibly more re levant, one ClCl interaction between the cores of the two units have been found responsible for novel magnetic intra-dimer interactions. This weak intermolecular exchange coupling present in a specific family of distorted tetranuclear manganese clusters ha s been investigated. A detailed study of the magnetic data of these complexes allowed the calculation of g, D, ST, J33, and J34. These complexes have a well-isolated S = 9/2 ground state spin, which is in agreement with the results found for other [Mn4O3X]6+ complexes (where X = MeCO2 -, PhCO2 -, Br-, F-, etc.). Each Mn4 is a single-molecule magnet with a S = 9/2 ground state and a large, negative

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182 anisotropy (D). Therefore, these complexes display frequency-dependent ac susceptibilities signals, and also exhibit magne tization hysteresis at temperatures below 1 K. The formation of [Mn4]2 has allowed the study of identic al, coupled particles with a S = 0 ground state. The anisotropy and exchange splitting in the excha nge-coupled dimer of SMMs [Mn4]2 was accurately determined by INS. The weak antiferromagnetic exchange interaction between the two Mn4 subunits within the dimer strongly depends on the intradimer distance. This distance can be chem ically modified either by exchanging the solvents of crystallization or by deuteration of the six hydrogens which connect the two subunits together via hydroge n-bonding. Deuteration has no measurable influence on the exchange coupling (below 5%), although it slightly shortens the intra-dimer separation. However, the change of the solvent of crys tallization not only shor tens the intra-dimer separation, but also decreases the inter-dimer interactions. Finally, the goal to identify the vibr ational modes of the dimer SMM, [Mn4]2, was achieved as many of the theo retically predicted Raman modes match well with the experimentally observed spectra. The data pr ovided here suggest the need for further refinement of the theoretical calculations and should elicit additional theoretical and experimental interest in the field of SMMs. They also prov ide the basis for studies of magnetic-field effects on these modes, as has been reported for Mn12-acetate The exchange-bias effect in [Mn4]2 demonstrates the feasibility of employing supramolecular chemistry to modulate th e quantum physics of SMMs, providing a realistic method for fine-tuning the propertie s of these molecular nanoscale materials.

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183 APPENDIX A BOND DISTANCES AND ANGLES Table A-1. Selected interatomic distances () and angles () for [Mn12(O2CMe)14(mda)8]2MeCN (1) (1MeCN) Mn1-O15 1.918(4) Mn4-O19 2.212(3) Mn1-O16 1.924(3) Mn4-O9 2.228(4) Mn1-O1 1.949(4) Mn4-O18 2.230(4) Mn1-O16 1.924(3) Mn4-O6 2.256(4) Mn1-O14 2.177(4) Mn4-O20 2.285(4) Mn1-N1 2.338(5) Mn4-N3 2.425(5) Mn2-O17 2.086(3) Mn5-O20 1.889(3) Mn2-O4 2.119(4) Mn5-O21 1.897(4) Mn2-O5 2.158(4) Mn5-O22 1.924(3) Mn2-O15 2.169(4) Mn5-O12 1.985(4) Mn2-O7 2.185(4) Mn5-O10 2.197(4) Mn2-O14 2.251(4) Mn5-N4 2.303(5) Mn3-O19 1.889(4) Mn6-O13 2.107(4) Mn3-O18 1.906(3) Mn6-O16 2.139(4) Mn3-O17 1.928(4) Mn6-O22 2.170(3) Mn3-O6 1.948(4) Mn6-O2 2.197(4) Mn3-O7 2.257(3) Mn6-O11 2.199(4) Mn3-N2 2.304(4) Mn6-O10 2.224(3) Mn4-O21 2.206(4) O15-Mn1-O16 94.36(16) O15-Mn1-O1 169.11(15) O16-Mn1-O1 91.60(16) O15-Mn1-O2 89.76(16) O16-Mn1-O3 171.70(17) O1-Mn1-O2 83.24(16) O15-Mn1-O14 82.40(15) O16-Mn1-O14 96.56(14) O1-Mn1-O14 105.99(15) O3-Mn1-O14 91.12(15) O15-Mn1-N1 78.63(17) O16-Mn1-N1 80.81(15) O1-Mn1-N1 93.36(17) O3-Mn1-N1 92.98(16) O14-Mn1-N1 160.56(16) O16-Mn1-N1 80.81(15) O17-Mn2-O4 173.89(15) O17-Mn2-O5 91.42(14) O4-Mn2-O5 94.17(14) O17-Mn2-O15 93.89(14) O4-Mn2-O15 88.70(14) O5-Mn2-O15 88.88(14) O17-Mn2-O7 77.14(13) O4-Mn2-O7 100.58(14) O5-Mn2-O7 87.90(14) O15-Mn2-O7 170.38(14) O17-Mn2-O14 89.15(14) O4-Mn2-O14 86.14(14) O5-Mn2-O14 164.27(14) O15-Mn2-O14 75.40(14) O7-Mn2-O14 107.53(14) O19-Mn3-O18 82.80(16) O19-Mn3-O17 178.23(16) O18-Mn3-O17 96.33(16)

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184 O19-Mn3-O6 89.06(16) O18-Mn3-O6 171.24(17) O17-Mn3-O6 91.89(16) O19-Mn3-O7 99.75(14) O18-Mn3-O7 87.27(14) O17-Mn3-O7 78.65(14) O6-Mn3-O7 97.34(14) O19-Mn3-N17 102.71(17) O18-Mn3-N2 82.43(16) O17-Mn3-N2 78.67(17) O6-Mn3-N2 96.29(16) O7-Mn3-N2 153.83(17) O21-Mn4-O19 148.91(14) O21-Mn4-O9 85.04(13) O19-Mn4-O9 88.46(13) O21-Mn4-O18 81.05(13) O19-Mn4-O18 68.81(13) O9-Mn4-O18 91.97(14) O21-Mn4-O8 93.25(13) O19-Mn4-O8 90.93(13) O9-Mn4-O8 175.58(15) O18-Mn4-O8 83.73(13) O21-Mn4-O20 67.79(13) O19-Mn4-O20 142.30(14) O9-Mn4-O2) 87.41(13) O18-Mn4-O20 148.77(13) O8-Mn4-O20 95.73(13) O21-Mn4-N3 138.13(14) O19-Mn4-N3 72.41(14) O9-Mn4-N3 92.32(15) O18-Mn4-N3 140.82(14) O8-Mn4-N3 91.67(14) O20-Mn4-N3 70.35(14) O20-Mn5-O21 82.83(15) O20-Mn5-O22 175.67(16) O21-Mn5-O22 94.57(15) O20-Mn5-O12 91.44(15) O21-Mn5-O12 172.75(15) O22-Mn5-O12 90.87(15) O20-Mn5-O10 100.78(14) O21-Mn5-O10 92.52(15) O22-Mn5-O10 82.75(14) O12-Mn5-O10 92.93(14) O20-Mn5-N4 96.45(15) O21-Mn5-N4 81.99(16) O22-Mn5-N4 79.73(15) O12-Mn5-N4 94.29(16) O10-Mn5-N4 161.13(15) O13-Mn6-O16 92.77(14) O13-Mn6-O22 97.11(14) O16-Mn6-O22 96.81(13) O13-Mn6-O2 93.74(15) O16-Mn6-O2 88.02(14) O22-Mn6-O2 167.88(14) O13-Mn6-O11 172.49(15) O16-Mn6-O11 94.64(14) O22-Mn6-O11 83.24(14) O2-Mn6-O11 85.30(14) O11-Mn6-O10 86.41(13) O16-Mn6-O10 173.45(14) O13-Mn6-O10 86.37(14) O2 -Mn6-O10 98.51(14) O22-Mn6-O10 76.88(13)

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185 Table A-2. Selected interatomic distances () and angles () for [Mn4(O2CPh)4(mda)2(mdaH)2]2CH2Cl2Et2O (2CH2Cl2Et2O) Mn1-O5 1.860(4) Mn1-O4 1.954(3) Mn2-O6 2.126(4)) Mn1-O4' 2.239(3) Mn1-O3 1.909(4) Mn1-N1 2.294(4) Mn1-O2 1.925(4) Mn2-O4 2.333(4) Mn2-O5 2.256(4) Mn2-N2 2.387(5) Mn2-O8 2.333(5) Mn2-O1' 2.429(4) Mn2-O3' 2.112(4) O5-Mn1-O3 172.70(15) O5-Mn1-O2 93.79(16) O3-Mn1-O2 92.33(16) O5-Mn1-O4 81.47(15) O3-Mn1-O4 92.71(15) O2-Mn1-O4 173.64(16) O5-Mn1-O4' 99.86(15) O3-Mn1-O4' 83.60(14) O2-Mn1-O4' 94.55(14) O4-Mn1-O4' 82.16(13) O5-Mn1-N1 96.51(17) O3-Mn1-N1 78.19(16) O2-Mn1-N1 103.37(17) O4-Mn1-N1 81.48(15) O4'-Mn1-N1 154.81(15) O3'-Mn2-O6 166.47(15) O3'-Mn2-O5 91.69(14) O6-Mn2-O5 97.18(14) O3'-Mn2-O8 91.74(16) O6-Mn2-O8 87.18(16) O5-Mn2-O8 143.62(15) O3'-Mn2-O4 77.10(13) O6-Mn2-O4 97.23(14) O5-Mn2-O4 65.69(12) O8-Mn2-O4 149.79(14) O3'-Mn2-N2 97.61(15) O6-Mn2-N2 94.90(16) O5-Mn2-N2 71.47(14) O8-Mn2-N2 72.18(16) O4-Mn2-N2 136.53(14) O3'-Mn2-O1' 78.04(13) O6-Mn2-O1' 88.66(14) O5-Mn2-O1' 140.96(14) O8-Mn2-O1' 4.95(15) O4-Mn2-O1' 75.30(13)

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186 Table A-3. Selected interatomic distances () and angles () for [Mn6O2(OH)2(dpa)8(mdaH)2]3MePh (3MePh) Mn1-O3 2.071(4) Mn2-O12 1.961(4) Mn1-O5 2.108(4) Mn2-O2 2.245(4) Mn1-O1 2.147(4) Mn2-O6 2.406(4) Mn1-O4 2.150(4) Mn3-O2 1.899(4) Mn1-O2 2.285(4) Mn3-O6 1.908(4) Mn1-O6 2.410(4) Mn3-O9 1.911(4) Mn2-O5 1.868(4) Mn3-N1 2.113(5) Mn2-O5 1.871(4) Mn3-O8 2.163(4) Mn2-O7 1.950(4) Mn3-O10 2.232(5) O3-Mn1-O5 173.30(15) O3-Mn1-O1 100.84(15) O5-Mn1-O1 85.46(14) O3-Mn1-O4 95.18(16) O5-Mn1-O4 83.61(14) O1-Mn1-O4 119.02(15) O3-Mn1-O2 99.37(16) O5-Mn1-O2 78.72(14) O1-Mn1-O2 85.30(14) O4-Mn1-O2 148.67(15) O3-Mn1-O6 92.83(15) O5-Mn1-O6 80.51(13) O1-Mn1-O6 150.62(14) O4-Mn1-O6 85.02(14) O2-Mn1-O6 66.76(13) O5-Mn2-O7 92.82(15) O5-Mn2-O5 83.50(16) O5 -Mn2-O7 175.69(17) O5-Mn2-O12 176.36(16) O5 -Mn2-O12 93.06(15) O7-Mn2-O12 90.58(15) O5-Mn2-O2 91.81(16) O5 -Mn2-O2 84.81(16) O7-Mn2-O2 97.57(16) O12 -Mn2-O2 89.02(15) O5-Mn2-O6 85.55(14) O5 -Mn2-O6 90.12(15) O7-Mn2-O6 87.36(15) O12 -Mn2-O6 93.32(14) O2 -Mn2-O6 174.52(14) O2-Mn3-O6 85.54(17) O2-Mn3-O9 96.86(17) O6-Mn3-O9 177.41(17) O2-Mn3-N1 168.04(19) O6-Mn3-N1 84.57(17) O9-Mn3-N1 92.93(18) O2-Mn3-O8 95.69(16) O6-Mn3-O8 92.72(16) O9-Mn3-O8 88.03(16) N1-Mn3-O8 91.49(17) O2-Mn3-O10 96.22(17) O6-Mn3-O10 95.23(16) O9-Mn3-O10 83.55(17) N1-Mn3-O10 78.02(18) O8-Mn3-O10 166.15(17) Mn3-O2-Mn2 125.5(2) Mn3-O2-Mn1 98.27(17) Mn2 -O2-Mn1 87.94(15) Mn2-O5-Mn2 96.50(16) Mn2-O5-Mn1 106.92(17) Mn2 -O5-Mn1 104.29(17) Mn3-O6-Mn2 121.48(17) Mn3-O6-Mn1 93.93(14) Mn2-O6-Mn1 83.22(12)

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187 Table A-4. Selected interatomic distances () and angles () for [Ni24(O2CMe)42(mdaH)6(EtOH)6]7H2O6MeCO2H12EtOH12Et2O (4H2O6MeCO2H12EtOH12Et2O) Ni1-O1 2.013(5) Ni2-O8 1.9953(19) Ni1-O4 2.032(2) Ni2-O7 2.0525(18) Ni1-O2 2.044(2) Ni2-O10 2.0755(18) Ni1-O5 2.066(2) Ni2-O12 2.0869(18) Ni1-O6 2.0754(19) Ni2-O6 2.0912(19) Ni1-N1 2.086(3) Ni2-O2 2.103(2) Ni3-O9 1.9988(19) Ni4-O16 2.0296(19) Ni3-O13' 2.0254(19) Ni4-O6 2.0386(18) Ni3-O14' 2.0312(19) Ni4-O12 2.0507(18) Ni3-O17' 2.034(2) Ni4-O11 2.0547(19) Ni3-O10 2.0981(18) Ni4-O14 2.0548(19) Ni3-O7 2.1228(19) Ni4-O15 2.165(2) O1-Ni1-O4 89.01(17) O1-Ni1-O5 82.63(17) O1-Ni1-O2 99.9(2) O4-Ni1-O5 169.78(9) O4-Ni1-O2 93.53(8) O2-Ni1-O5 93.70(9) O1-Ni1-O6 176.74(17) O4-Ni1-O6 94.24(8) O2-Ni1-O6 79.98(8) O5-Ni1-O6 94.12(9) O1-Ni1-N1 94.6(2) O4-Ni1-N1 92.76(10) O2-Ni1-N1 164.28(10) O5-Ni1-N1 82.11(11) O6-Ni1-N1 85.20(10) O1-Ni1-O1' 12.3(2) O4-Ni1-O1' 90.98(16) O2-Ni1-O1' 87.67(18) O5-Ni1-O1' 82.10(15) O6-Ni1-O1' 166.85(18) N1-Ni1-O1' 106.61(19) O8-Ni2-O7 87.35(8) O8-Ni2-O10 101.04(7) O7-Ni2-O10 79.93(7) O8-Ni2-O12 95.13(7) O7-Ni2-O12 166.46(7) O10-Ni2-O12 86.52(7) O8-Ni2-O6 167.07(8) O7-Ni2-O6 93.55(7) O10-Ni2-O6 91.82(7) O12-Ni2-O6 87.00(7) O8-Ni2-O2 88.87(8) O7-Ni2-O2 100.79(8) O10-Ni2-O2 170.09(8) O12-Ni2-O2 92.58(7) O6-Ni2-O2 78.28(8) O9-Ni3-O13' 178.44(8) O9-Ni3-O14' 91.27(8) O13'-Ni3-O14' 90.04(8) O9-Ni3-O17' 86.38(8) O13'-Ni3-O17' 94.42(8) O14'-Ni3-O17' 91.77(8) O9-Ni3-O10 91.25(8) O13'-Ni3-O10 87.77(7) O14'-Ni3-O10 96.45(7) O17'-Ni3-O10 171.50(8) O9-Ni3-O7 91.93(8) O13'-Ni3-O7 86.68(8) O14'-Ni3-O7 173.52(7) O17'-Ni3-O7 94.07(8) O10-Ni3-O7 77.84(7) O16-Ni4-O6 94.25(8) O16-Ni4-O12 90.54(8) O6-Ni4-O12 89.39(7) O16-Ni4-O11 175.73(8) O6-Ni4-O11 89.15(7) O12-Ni4-O11 86.91(7) O16-Ni4-O14 89.57(8) O6-Ni4-O14 165.92(8) O12-Ni4-O14 104.15(8)

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188 O11-Ni4-O14 87.74(7) O16-Ni4-O15 91.67(8) O6-Ni4-O15 103.92(8) O12-Ni4-O15 166.30(8) O11-Ni4-O15 90.02(8) O14-Ni4-O15 62.36(8) O16-Ni4-C20 91.02(9) O6-Ni4-C20 134.71(9) O12-Ni4-C20 135.57(9) O11-Ni4-C20 88.42(8) O14-Ni4-C20 31.48(8) O15-Ni4-C20 30.88(8) O16-Ni4-Ni2 101.32(6) O6-Ni4-Ni2 45.31(5) O12-Ni4-Ni2 45.19(5) O11-Ni4-Ni2 79.26(5) O14-Ni4-Ni2 146.74(6) O15-Ni4-Ni2 146.84(6) Ni1-O2-Ni2 93.95(8) Ni4-O6-Ni1 132.00(10) Ni4-O6-Ni2 90.82(7) Ni1-O6-Ni2 93.36(8) Ni2-O7-Ni3 95.37(8) Ni2-O10-Ni3 95.44(7) Ni4-O12-Ni2 90.61(7) Ni3'-O14-Ni4 112.29(9)

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189 Table A-5. Selected interatomic dist ances () and angles () for [Ni(mdaH2)2](O2CMe)2 (5) Ni-O2 2.0644(11) Ni-O1' 2.0848(11) Ni-O2' 2.0644(11) Ni-O1 2.0848(11) Ni-N1 2.0923(13) Ni-N1' 2.0923(13) O2-Ni-O2' 180.0 O2-Ni-N1' 95.94(5) O2-Ni-O1' 87.06(5) O2'-Ni-N1' 84.06(5) O2'-Ni-O1' 92.94(5) O1'-Ni-N1' 82.31(5) O1-Ni-N1' 97.69(5)

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190 Table A-6. Selected interatomic distances () and angles () for [Fe22O14(OH)3(O2CMe)21(mda)6](ClO4)2H2O4EtOH4Et2O (6H2O4EtOH4Et2O) Fe1-O1 1.888(9) Fe2-O3 1.912(9) Fe1-O2 2.011(9) Fe2-O8 1.924(10) Fe1-O3 2.012(9) Fe2-O9 1.931(9) Fe1-O4 2.017(11) Fe2-O6 2.083(9) Fe1-O5 2.028(10) Fe2-O7 2.093(8) Fe1-N1 2.191(11) Fe2-O1 2.104(9) Fe3-O7 1.897(9) Fe3-O8 1.987(9) Fe3-O11 2.016(12) Fe3-O10 2.025(10) Fe3-O12 2.027(10) Fe3-N3 2.167(14) Fe4-O6 1.908(8) Fe4-O13 1.978(9) Fe4-O9 1.997(10) Fe4-O15 2.014(12) Fe4-O14 2.042(12) Fe4-N2 2.189(13) Fe5-O10 1.956(11) Fe5-O16 1.960(9) Fe5-O1 1.972(8) Fe5-O18 2.030(9) Fe5-O19 2.045(10) Fe5-O17 2.115(10) Fe6-O20 1.909(8) Fe6-O2 1.943(10) Fe6-O6 2.020(9) Fe6-O22 2.040(11) Fe6-O23 2.080(10) Fe6-O21 2.089(10) Fe7-O16 1.906(9) Fe7-O24 1.929(8) Fe7-O20 1.930(9) Fe7-O6 2.085(8) Fe7-O7 2.162(9) Fe7-O1 2.215(9) Fe8-O24 1.956(8) Fe8-O13 1.980(10) Fe8-O7 1.994(9) Fe8-O26 1.997(11) Fe8-O27 2.055(11) Fe8-O25 2.133(11) Fe9-O20 1.850(8) Fe9-O29 1.966(8) Fe9-O31 2.013(9) Fe9-O30 2.015(11) Fe9-O28 2.016(9) Fe10-O16 1.876(9) Fe10-O28 2.010(9) Fe10-O33 2.012(9) Fe10-O34 2.072(8) Fe10-O32 2.101(8) Fe10-O29 2.129(9) Fe11-O24 1.872(8) Fe11-O29 1.933(8) Fe11-O37 1.987(10) Fe11-O36 1.997(10) Fe11-O35 2.120(8) Fe11-O34 2.132(8) Fe12-O38 1.860(8) Fe12-O39 2.038(10) Fe12-O29 2.042(8) Fe12-O35 2.052(8) Fe12-O40 2.066(10) Fe12-O32 2.108(9) Fe13-O41 1.842(8) Fe13-O43 1.983(9) Fe13-O42 2.018(9) Fe13-O32 2.055(8) Fe13-O35 2.092(8) Fe13-O34 2.118(8) Fe14-O44 1.850(8) Fe14-O35 1.938(9) Fe14-O46 1.960(9) Fe14-O45 1.964(10) Fe14-O47 2.072(10) Fe15-O48 1.938(8) Fe15-O51 1.994(9) Fe15-O49 2.010(8) Fe15-O50 2.024(9)

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191 Fe15-O52 2.046(9) Fe15-N5 2.219(10) Fe16-O38 1.940(8) Fe16-O48 1.970(8) Fe16-O53 1.998(9) Fe16-O54 2.039(9) Fe16-O55 2.066(9) Fe16-O56 2.133(10) Fe17-O44 1.909(8) Fe17-O41 1.915(8) Fe17-O38 1.924(8) Fe17-O57 2.095(8) Fe17-O58 2.143(8) Fe17-O48 2.165(8) Fe18-O41 1.960(8) Fe18-O58 1.973(9) Fe18-O49 1.977(8) Fe18-O61 2.018(9) Fe18-O62 2.062(9) Fe18-O60 2.064(10) Fe19-O44 1.937(8) Fe19-O63 1.991(9) Fe19-O57 2.016(8) Fe19-O66 2.020(9) Fe19-O65 2.055(10) Fe19-O64 2.082(10) Fe20-O58 1.912(8) Fe20-O59 1.981(10) Fe20-O67 1.992(9) Fe20-O68 2.011(10) Fe20-O63 2.013(9) Fe20-N6 2.235(11) Fe21-O50 1.908(8) Fe21-O67 1.928(8) Fe21-O69 1.948(9) Fe21-O48 2.073(8) Fe21-O57 2.087(8) Fe21-O58 2.129(8) Fe22-O57 1.918(8) Fe22-O53 1.973(9) Fe22-O71 1.996(10) Fe22-O69 2.009(8) Fe22-O70 2.041(11) Fe22-N4 2.249(11) O1-Fe1-O2 94.3(4) O1-Fe1-O3 81.6(4) O2-Fe1-O3 98.5(4) O1-Fe1-O4 97.3(4) O2-Fe1-O4 167.4(4) O3-Fe1-O4 87.9(4) O1-Fe1-O5 104.5(4) O2-Fe1-O5 85.4(4) O3-Fe1-O5 172.6(4) O4-Fe1-O5 87.1(4) O1-Fe1-N1 159.4(4) O2-Fe1-N1 82.0(4) O3-Fe1-N1 79.0(4) O4-Fe1-N1 88.7(4) O5-Fe1-N1 95.4(4) O3-Fe2-O8 96.4(4) O3-Fe2-O9 100.2(4) O8-Fe2-O9 101.1(4) O3-Fe2-O6 103.5(4) O8-Fe2-O6 159.9(4) O9-Fe2-O6 78.1(4) O3-Fe2-O7 157.8(4) O8-Fe2-O7 78.5(4) O9-Fe2-O7 102.0(4) O6-Fe2-O7 82.0(3) O3-Fe2-O1 78.7(3) O8-Fe2-O1 101.9(4) O9-Fe2-O1 157.0(4) O6-Fe2-O1 79.9(3) O7-Fe2-O1 81.3(4) O7-Fe3-O8 81.9(4) O7-Fe3-O11 99.1(5) O8-Fe3-O11 86.5(4) O7-Fe3-O10 94.2(4) O8-Fe3-O10 98.4(4) O11-Fe3-O10 166.3(5) O7-Fe3-O12 104.0(4) O8-Fe3-O12 171.8(4) O11-Fe3-O12 86.8(5) O10-Fe3-O12 87.0(4) O7-Fe3-N3 160.0(4) O8-Fe3-N3 79.5(4) O11-Fe3-N3 86.8(6) O10-Fe3-N3 81.6(5) O12-Fe3-N3 95.3(5) O6-Fe4-O13 98.9(4)

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192 O6-Fe4-O9 80.8(4) O13-Fe4-O9 96.4(4) O6-Fe4-O15 101.9(4) O13-Fe4-O15 87.9(5) O9-Fe4-O15 174.5(4) O6-Fe4-O14 96.1(4) O13-Fe4-O14 164.7(4) O9-Fe4-O14 89.0(4) O15-Fe4-O14 86.0(5) O6-Fe4-N2 159.1(5) O13-Fe4-N2 82.0(5) O9-Fe4-N2 78.4(5) O15-Fe4-N2 99.0(5) O14-Fe4-N2 85.1(5) O10-Fe5-O16 95.7(4) O10-Fe5-O1 93.9(4) O16-Fe5-O1 86.5(4) O10-Fe5-O18 90.1(4) O16-Fe5-O18 90.1(4) O1-Fe5-O18 175.0(4) O10-Fe5-O19 87.4(4) O16-Fe5-O19 176.1(4) O1-Fe5-O19 95.6(4) O18-Fe5-O19 87.5(4) O10-Fe5-O17 171.3(4) O16-Fe5-O17 91.5(4) O1-Fe5-O17 91.3(4) O18-Fe5-O17 85.1(4) O19-Fe5-O17 85.2(4) O20-Fe6-O2 98.3(4) O20-Fe6-O6 84.1(4) O2-Fe6-O6 94.5(4) O20-Fe6-O22 93.8(4) O2-Fe6-O22 165.4(4) O6-Fe6-O22 94.8(4) O20-Fe6-O23 176.0(4) O2-Fe6-O23 85.6(4) O6-Fe6-O23 96.5(4) O22-Fe6-O23 82.1(4) O20-Fe6-O21 89.3(4) O2-Fe6-O21 87.1(4) O6-Fe6-O21 173.4(4) O22-Fe6-O21 84.9(4) O23-Fe6-O21 90.0(4) O16-Fe7-O24 99.3(3) O16-Fe7-O20 98.8(4) O24-Fe7-O20 102.6(4) O16-Fe7-O6 158.5(4) O24-Fe7-O6 101.5(3) O20-Fe7-O6 81.9(3) O16-Fe7-O7 96.9(3) O24-Fe7-O7 83.1(3) O20-Fe7-O7 162.1(3) O6-Fe7-O7 80.4(3) O16-Fe7-O1 81.3(3) O24-Fe7-O1 160.3(3) O20-Fe7-O1 96.8(3) O6-Fe7-O1 77.3(3) O7-Fe7-O1 77.3(3) O24-Fe8-O7 87.0(4) O13-Fe8-O7 93.9(4) O24-Fe8-O26 94.6(4) O13-Fe8-O26 89.6(4) O7-Fe8-O26 176.1(4) O24-Fe8-O27 176.9(4) O13-Fe8-O27 90.1(4) O7-Fe8-O27 94.4(4) O26-Fe8-O27 83.9(4) O24-Fe8-O25 89.6(4) O13-Fe8-O25 175.4(4) O7-Fe8-O25 90.3(4) O26-Fe8-O25 86.2(4) O27-Fe8-O25 87.7(4) O20-Fe9-O29 93.9(3) O20-Fe9-O31 93.7(4) O29-Fe9-O31 172.0(4) O20-Fe9-O30 108.7(4) O29-Fe9-O30 90.6(4) O31-Fe9-O30 84.7(4) O20-Fe9-O28 101.7(4) O29-Fe9-O28 83.5(4) O31-Fe9-O28 97.3(4) O30-Fe9-O28 149.4(4) O16-Fe10-O28 93.9(4) O16-Fe10-O33 93.5(4) O28-Fe10-O33 98.7(4) O16-Fe10-O34 90.8(3) O28-Fe10-O34 157.0(3) O33-Fe10-O34 103.4(3) O16-Fe10-O32 165.9(3) O28-Fe10-O32 98.6(3) O33-Fe10-O32 91.0(3)

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193 O34-Fe10-O32 75.2(3) O16-Fe10-O29 100.7(3) O28-Fe10-O29 79.6(3) O33-Fe10-O29 165.8(3) O34-Fe10-O29 77.4(3) O32-Fe10-O29 75.4(3) O24-Fe11-O29 97.0(3) O24-Fe11-O37 97.0(4) O29-Fe11-O37 95.6(4) O24-Fe11-O36 94.2(4) O29-Fe11-O36 168.4(4) O37-Fe11-O36 86.1(4) O24-Fe11-O35 171.3(3) O29-Fe11-O35 81.5(3) O37-Fe11-O35 91.8(4) O36-Fe11-O35 87.0(3) O24-Fe11-O34 94.1(3) O29-Fe11-O34 80.4(3) O37-Fe11-O34 168.7(4) O36-Fe11-O34 95.7(4) O35-Fe11-O34 77.2(3) O38-Fe12-O39 102.5(4) O38-Fe12-O29 166.9(4) O39-Fe12-O29 90.4(4) O38-Fe12-O35 98.7(3) O39-Fe12-O35 100.5(4) O29-Fe12-O35 80.6(3) O38-Fe12-O40 96.2(4) O39-Fe12-O40 84.0(4) O29-Fe12-O40 83.0(4) O35-Fe12-O40 163.0(4) O38-Fe12-O32 89.9(3) O39-Fe12-O32 166.8(4) O29-Fe12-O32 77.1(3) O35-Fe12-O32 81.8(3) O40-Fe12-O32 90.2(3) O41-Fe13-O43 104.4(4) O41-Fe13-O42 93.4(4) O43-Fe13-O42 87.5(4) O41-Fe13-O32 96.9(3) O43-Fe13-O32 158.7(4) O42-Fe13-O32 92.5(3) O41-Fe13-O35 93.4(3) O43-Fe13-O35 95.2(4) O42-Fe13-O35 171.7(4) O32-Fe13-O35 82.1(3) O41-Fe13-O34 169.0(3) O43-Fe13-O34 83.6(3) O42-Fe13-O34 94.5(3) O32-Fe13-O34 75.1(3) O35-Fe13-O34 78.1(3) O44-Fe14-O35 96.7(3) O44-Fe14-O46 118.1(4) O35-Fe14-O46 93.4(4) O44-Fe14-O45 113.5(4) O35-Fe14-O45 98.1(4) O46-Fe14-O45 125.2(4) O44-Fe14-O47 92.4(4) O35-Fe14-O47 170.9(4) O46-Fe14-O47 82.1(4) O45-Fe14-O47 78.4(4) O48-Fe15-O51 104.8(4) O48-Fe15-O49 94.5(3) O51-Fe15-O49 87.8(4) O48-Fe15-O50 82.1(3) O51-Fe15-O50 170.1(3) O49-Fe15-O50 98.8(3) O48-Fe15-O52 97.9(4) O51-Fe15-O52 86.1(4) O49-Fe15-O52 167.2(4) O50-Fe15-O52 85.9(4) O48-Fe15-N5 160.9(4) O51-Fe15-N5 93.8(4) O49-Fe15-N5 81.9(4) O50-Fe15-N5 79.9(4) O52-Fe15-N5 87.4(4) O38-Fe16-O48 86.4(3) O38-Fe16-O53 94.7(3) O48-Fe16-O53 92.6(3) O38-Fe16-O54 93.5(3) O48-Fe16-O54 173.0(4) O53-Fe16-O54 94.4(4) O38-Fe16-O55 176.7(4) O48-Fe16-O55 93.6(3) O53-Fe16-O55 88.6(4) O54-Fe16-O55 86.2(3) O38-Fe16-O56 88.9(3) O48-Fe16-O56 89.5(3) O53-Fe16-O56 176.0(3) O54-Fe16-O56 83.5(4) O55-Fe16-O56 87.9(4) O44-Fe17-O41 98.8(3)

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194 O44-Fe17-O38 102.8(3) O41-Fe17-O38 96.4(3) O44-Fe17-O57 81.4(3) O41-Fe17-O57 161.6(3) O38-Fe17-O57 101.5(3) O44-Fe17-O58 98.6(3) O41-Fe17-O58 81.7(3) O38-Fe17-O58 158.6(3) O57-Fe17-O58 80.0(3) O44-Fe17-O48 160.0(3) O41-Fe17-O48 100.1(3) O38-Fe17-O48 81.5(3) O57-Fe17-O48 78.5(3) O58-Fe17-O48 77.9(3) O41-Fe18-O58 85.1(3) O41-Fe18-O49 98.4(3) O58-Fe18-O49 92.0(3) O41-Fe18-O61 89.3(3) O58-Fe18-O61 174.4(3) O49-Fe18-O61 88.4(3) O41-Fe18-O62 176.3(4) O58-Fe18-O62 95.1(3) O49-Fe18-O62 85.3(3) O61-Fe18-O62 90.5(4) O41-Fe18-O60 92.3(3) O58-Fe18-O60 93.6(4) O49-Fe18-O60 168.3(4) O61-Fe18-O60 87.0(4) O62-Fe18-O60 83.9(3) O44-Fe19-O63 96.5(4) O44-Fe19-O57 82.8(3) O63-Fe19-O57 94.9(4) O44-Fe19-O66 93.0(4) O63-Fe19-O66 87.2(4) O57-Fe19-O66 175.5(4) O44-Fe19-O65 176.0(4) O63-Fe19-O65 83.3(4) O57-Fe19-O65 93.2(4) O66-Fe19-O65 91.0(4) O44-Fe19-O64 94.8(4) O63-Fe19-O64 166.6(4) O57-Fe19-O64 93.7(4) O66-Fe19-O64 85.0(4) O65-Fe19-O64 86.0(4) O58-Fe20-O59 102.5(4) O58-Fe20-O67 82.9(4) O59-Fe20-O67 173.5(4) O58-Fe20-O68 98.2(4) O59-Fe20-O68 87.1(4) O67-Fe20-O68 88.6(4) O58-Fe20-O63 96.7(4) O59-Fe20-O63 87.4(4) O67-Fe20-O63 95.5(4) O68-Fe20-O63 165.0(4) O58-Fe20-N6 159.5(4) O59-Fe20-N6 97.7(4) O67-Fe20-N6 77.1(4) O68-Fe20-N6 86.0(5) O63-Fe20-N6 80.9(5) O50-Fe21-O67 95.9(4) O50-Fe21-O69 99.5(4) O67-Fe21-O69 101.2(4) O50-Fe21-O48 81.6(3) O67-Fe21-O48 158.0(3) O69-Fe21-O48 100.7(3) O50-Fe21-O57 161.6(4) O67-Fe21-O57 102.5(4) O69-Fe21-O57 78.4(3) O48-Fe21-O57 80.8(3) O50-Fe21-O58 101.8(3) O67-Fe21-O58 79.0(3) O69-Fe21-O58 158.5(3) O48-Fe21-O58 80.2(3) O57-Fe21-O58 80.6(3) O50-Fe21-Fe17 121.6(3) O57-Fe22-O53 97.7(4) O57-Fe22-O71 104.1(4) O53-Fe22-O71 88.7(4) O57-Fe22-O69 81.1(3) O53-Fe22-O69 96.9(4) O71-Fe22-O69 171.9(4) O57-Fe22-O70 97.8(4) O53-Fe22-O70 164.5(4) O71-Fe22-O70 87.0(4) O69-Fe22-O70 86.1(4) O57-Fe22-N4 160.1(4) O53-Fe22-N4 79.8(4) O71-Fe22-N4 95.6(4) O69-Fe22-N4 79.7(4) O70-Fe22-N4 85.8(5) Fe1-O1-Fe5 116.7(5) Fe1-O1-Fe2 97.5(4)

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195 Fe5-O1-Fe2 135.2(5) Fe1-O1-Fe7 135.9(5) Fe5-O1-Fe7 90.7(3) Fe2-O1-Fe7 82.7(3) Fe6-O2-Fe1 129.9(5) Fe4-O6-Fe6 117.3(4) Fe4-O6-Fe2 97.9(4) Fe6-O6-Fe2 134.0(4) Fe4-O6-Fe7 129.4(4) Fe6-O6-Fe7 92.3(3) Fe2-O6-Fe7 86.5(3) Fe3-O7-Fe8 116.3(5) Fe3-O7-Fe2 97.2(4) Fe8-O7-Fe2 134.7(5) Fe3-O7-Fe7 136.4(5) Fe8-O7-Fe7 90.4(4) Fe2-O7-Fe7 84.3(3) Fe2-O8-Fe3 100.1(4) Fe2-O9-Fe4 100.1(4) Fe5-O10-Fe3 129.6(5) Fe4-O13-Fe8 128.8(5) Fe10-O16-Fe7 119.7(4) Fe10-O16-Fe5 130.9(5) Fe7-O16-Fe5 101.0(4) Fe9-O20-Fe6 132.9(5) Fe9-O20-Fe7 125.4(4) Fe6-O20-Fe7 100.9(4) Fe11-O24-Fe7 124.1(4) Fe11-O24-Fe8 127.8(4) Fe7-O24-Fe8 98.9(4) Fe10-O28-Fe9 96.7(4) Fe11-O29-Fe9 141.9(4) Fe11-O29-Fe12 101.0(4) Fe9-O29-Fe12 108.9(4) Fe11-O29-Fe10 100.8(4) Fe9-O29-Fe10 94.5(3) Fe12-O29-Fe10 103.7(3) Fe13-O32-Fe10 104.6(3) Fe13-O32-Fe12 95.8(3) Fe10-O32-Fe12 102.5(3) Fe10-O34-Fe13 103.4(3) Fe10-O34-Fe11 96.4(3) Fe13-O34-Fe11 101.5(3) Fe14-O35-Fe12 128.3(4) Fe14-O35-Fe13 113.8(4) Fe12-O35-Fe13 96.4(3) Fe14-O35-Fe11 116.4(4) Fe12-O35-Fe11 94.7(3) Fe13-O35-Fe11 102.8(4) Fe12-O38-Fe17 123.3(4) Fe12-O38-Fe16 131.2(5) Fe17-O38-Fe16 100.1(4) Fe13-O41-Fe17 127.7(4) Fe13-O41-Fe18 130.9(4) Fe17-O41-Fe18 100.1(4) Fe14-O44-Fe17 124.8(4) Fe14-O44-Fe19 132.7(4) Fe17-O44-Fe19 101.8(4) Fe15-O48-Fe16 116.0(4) Fe15-O48-Fe21 95.7(3) Fe16-O48-Fe21 137.6(4) Fe15-O48-Fe17 134.5(4) Fe16-O48-Fe17 91.4(3) Fe21-O48-Fe17 84.4(3) Fe18-O49-Fe15 130.5(4) Fe21-O50-Fe15 98.3(4) Fe22-O53-Fe16 129.0(4) Fe22-O57-Fe19 116.2(4) Fe22-O57-Fe21 98.0(3) Fe19-O57-Fe21 133.4(4) Fe22-O57-Fe17 131.5(5) Fe19-O57-Fe17 93.1(3) Fe21-O57-Fe17 85.8(3) Fe20-O58-Fe18 116.4(4) Fe20-O58-Fe21 96.0(4) Fe18-O58-Fe21 136.6(4) Fe20-O58-Fe17 134.1(4) Fe18-O58-Fe17 92.3(3) Fe21-O58-Fe17 83.6(3) Fe19-O63-Fe20 128.3(5) Fe21-O67-Fe20 100.2(4) Fe21-O69-Fe22 99.7(4)

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196 Table A-7. Selected interatomic distances () and angles () for [Fe7NaO3(O2CPh)9(mda)3]ClO4Et2O (7Et2O) Fe1-O5 1.861(2) Fe2-O10 1.916(2) Fe1-O6 1.979(2) Fe2-O9 1.979(2) Fe1-O2 1.984(2) Fe2-O7 1.991(2) Fe1-O1 2.067(2) Fe2-O6 2.006(2) Fe1-O3 2.120(2) Fe2-O8 2.065(2) Fe1-O4 2.157(2) Fe2-N1 2.221(3) Fe3-O10 1.860(2) Fe4-O18 1.966(2) Fe3-O15 1.968(2) Fe4-O16 1.972(2) Fe3-O12 2.001(2) Fe4-O9 1.977(2) Fe3-O11 2.068(2) Fe4-O10 2.024(2) Fe3-O13 2.131(2) Fe4-O17 2.038(2) Fe3-O14 2.141(2) Fe4-O5 2.044(2) Fe5-O5 1.918(2) Fe6-O17 1.861(2) Fe5-O18 1.977(2) Fe6-O21 1.976(2) Fe5-O20 1.993(2) Fe6-O24 1.992(2) Fe5-O21 2.011(2) Fe6-O25 2.051(2) Fe5-O19 2.057(2) Fe6-O22 2.093(2) Fe5-N2 2.218(3) Fe6-O23 2.204(2) Fe7-O17 1.916(2) Na1-O14 2.191(2) Fe7-O16 1.983(2) Na1-O22 2.235(3) Fe7-O26 2.078(2) Na1-O4 2.259(3) Fe7-O27 1.999(2) Na1-O5 2.507(2) Fe7-O15 2.003(2) Na1-O17 2.580(2) Fe7-N3 2.217(3) Na1-O10 2.584(2) O5-Fe1-O6 94.13(9) O5-Fe1-O2 104.64(9) O6-Fe1-O2 91.38(10) O5-Fe1-O1 91.19(9) O6-Fe1-O1 172.82(10) O2-Fe1-O1 91.94(10) O5-Fe1-O3 160.45(9) O6-Fe1-O3 87.79(9) O2-Fe1-O3 94.75(9) O1-Fe1-O3 85.59(9) O5-Fe1-O4 99.18(9) O6-Fe1-O4 89.43(9) O2-Fe1-O4 156.04(9) O1-Fe1-O4 84.96(9) O3-Fe1-O4 61.35(9) O10-Fe2-O9 81.75(9) O10-Fe2-O7 99.72(9) O9-Fe2-O7 175.86(10) O10-Fe2-O6 98.77(9) O9-Fe2-O6 94.57(9) O7-Fe2-O6 89.03(10) O10-Fe2-O8 96.45(9) O9-Fe2-O8 89.92(9) O7-Fe2-O8 86.08(10) O6-Fe2-O8 164.60(9) O10-Fe2-N1 161.48(10) O9-Fe2-N1 79.98(10) O7-Fe2-N1 98.71(10) O6-Fe2-N1 79.74(10) O8-Fe2-N1 86.57(10) O10-Fe3-O15 96.53(9) O10-Fe3-O12 103.22(9) O15-Fe3-O12 90.94(10) O10-Fe3-O11 94.82(9) O15-Fe3-O11 168.50(9) O12-Fe3-O11 88.26(10) O10-Fe3-O13 155.93(9) O15-Fe3-O13 85.14(9)

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197 O12-Fe3-O13 100.76(9) O11-Fe3-O13 83.74(9) O10-Fe3-O14 94.49(9) O15-Fe3-O14 89.30(9) O12-Fe3-O14 162.14(9) O11-Fe3-O14 87.97(9) O13-Fe3-O14 61.47(8) O18-Fe4-O16 95.49(9) O18-Fe4-O9 92.64(10) O16-Fe4-O9 94.08(9) O18-Fe4-O10 162.07(9) O16-Fe4-O10 100.94(9) O9-Fe4-O10 79.18(9) O18-Fe4-O17 101.13(9) O16-Fe4-O17 78.75(9) O9-Fe4-O17 164.97(9) O10-Fe4-O17 89.15(9) O18-Fe4-O5 78.85(9) O16-Fe4-O5 163.63(9) O9-Fe4-O5 101.47(9) O10-Fe4-O5 87.11(8) O17-Fe4-O5 87.21(9) O5-Fe5-O18 81.69(9) O5-Fe5-O20 99.48(9) O18-Fe5-O20 177.24(10) O5-Fe5-O21 97.05(9) O18-Fe5-O21 94.80(10) O20-Fe5-O21 87.55(10) O5-Fe5-O19 97.33(9) O18-Fe5-O19 90.94(10) O20-Fe5-O19 86.43(10) O21-Fe5-O19 165.15(9) O5-Fe5-N2 160.93(10) O18-Fe5-N2 79.70(10) O20-Fe5-N2 99.29(11) O21-Fe5-N2 80.45(10) O19-Fe5-N2 87.14(10) O17-Fe6-O21 96.85(10) O17-Fe6-O24 102.54(10) O21-Fe6-O24 89.40(10) O17-Fe6-O25 96.47(10) O21-Fe6-O25 166.60(10) O24-Fe6-O25 86.35(11) O17-Fe6-O22 95.98(9) O21-Fe6-O22 93.96(10) O24-Fe6-O22 160.65(10) O25-Fe6-O22 86.03(10) O17-Fe6-O23 156.74(9) O21-Fe6-O23 85.62(10) O24-Fe6-O23 100.60(9) O25-Fe6-O23 82.69(10) O22-Fe6-O23 60.76(9) O17-Fe7-O16 81.46(9) O17-Fe7-O27 101.45(10) O16-Fe7-O27 175.44(10) O17-Fe7-O15 98.66(9) O16-Fe7-O15 93.07(9) O27-Fe7-O15 89.97(10) O17-Fe7-O26 95.44(9) O16-Fe7-O26 87.97(10) O27-Fe7-O26 88.26(10) O15-Fe7-O26 165.86(9) O17-Fe7-N3 162.13(11) O16-Fe7-N3 80.87(10) O27-Fe7-N3 96.35(11) O15-Fe7-N3 79.63(10) O26-Fe7-N3 86.62(10) Fe1-O5-Fe5 114.34(10) Fe1-O5-Fe4 136.51(12) Fe5-O5-Fe4 97.81(9) Fe1-O6-Fe2 128.87(11) Fe4-O9-Fe2 97.24(10) Fe3-O10-Fe2 116.38(11) Fe3-O10-Fe4 134.39(11) Fe2-O10-Fe4 97.75(9) Fe3-O15-Fe7 129.71(11) Fe4-O16-Fe7 98.07(10) Fe6-O17-Fe7 116.00(11) Fe6-O17-Fe4 134.72(12) Fe7-O17-Fe4 98.04(10) Fe4-O18-Fe5 98.54(10) Fe6-O21-Fe5 129.19(11)

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198 Table A-8. Selected interatomic distances () and angles () for [Fe7O3(O2CPh)9(mda)3(H2O)] (8) Fe1-O7 1.879(2) Fe1-O1 2.012(3) Fe1-O2 1.980(2) Fe1-O3 2.080(3) Fe1-O5 2.005(3) Fe1-N1 2.229(3) Fe2-O2 1.994(2) Fe2-O7A 1.994(2) Fe2-O2A 1.994(2) Fe2-O7 1.994(2) Fe3-O7 1.835(2) Fe3-O1A 2.005(3) Fe3-O10 2.017(4) Fe3-O4 2.027(3) Fe3-O6 2.078(3) Fe3-O9 2.133(3) Fe3-O8 2.236(9) O7-Fe1-O2 80.99(10) O7-Fe1-O5 100.80(11) O2-Fe1-O5 176.27(11) O7-Fe1-O1 96.24(10) O2-Fe1-O1 95.68(10) O5-Fe1-O1 87.40(12) O7-Fe1-O3 96.18(10) O2-Fe1-O3 90.82(10) O5-Fe1-O3 85.74(12) O1-Fe1-O3 166.75(11) O7-Fe1-N1 159.23(11) O2-Fe1-N1 79.04(11) O5-Fe1-N1 99.47(11) O1-Fe1-N1 80.18(11) O3-Fe1-N1 89.77(12) O2-Fe2-O2A 91.30(10) O2-Fe2-O7A 162.66(10) O2-Fe2-O7 77.92(9) O2A-Fe2-O7 102.36(10) O2 -Fe2-O7 162.66(10) O7A-Fe2-O7 91.02(10) O7-Fe2-O7A 91.03(10) O7-Fe3-O1A 94.28(11) O7-Fe3-O10 109.72(14) O1A-Fe3-O10 91.48(14) O7-Fe3-O4 98.10(11) O1A-Fe3-O4 88.89(11) O10-Fe3-O4 152.06(14) O7-Fe3-O6 94.43(11) O1A-Fe3-O6 170.76(10) O10-Fe3-O6 88.49(14) O4-Fe3-O6 86.83(11) O7-Fe3-O9 170.80(13) O1A-Fe3-O9 85.95(11) O10-Fe3-O9 61.09(16) O4-Fe3-O9 91.09(13) O6-Fe3-O9 85.94(11) O7-Fe3-O8 82.8(3) O1A-Fe3-O8 97.9(2) O10-Fe3-O8 27.3(2) O4-Fe3-O8 173.1(2) O6-Fe3-O8 86.3(2) O9-Fe3-O8 88.1(3) Fe3A-O1-Fe1 128.59(13) Fe1-O2-Fe2 96.57(10) Fe3-O7-Fe1 119.52(12) Fe3-O7-Fe2 135.09(13) Fe1-O7-Fe2 99.92(10)

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199 Table A-9. Selected interatomic distances () and angles () for [Fe7O3(O2CtBu)9(mda)3(H2O)3] (9) Fe1-O1 1.987(4) Fe1-O2 2.021(4) Fe1-O1 1.987(4) Fe1-O2 2.021(4) Fe1-O1 1.987(4) Fe1-O2 2.021(4) Fe2-O2 1.881(4) Fe2-O3 2.009(4) Fe2-O1 1.977(4) Fe2-O5 2.025(4) Fe2-O4 2.046(4) Fe2-N1 2.233(5) Fe3-O2 1.863(4) Fe3-O3 1.987(4) Fe3-O7 2.031(4) Fe3-O10 2.036(4) Fe3-O6 2.076(4) Fe3-O8 2.083(4) O1-Fe1-O1 93.06(16) O1-Fe1-O1 93.06(16) O1 -Fe1-O1 93.06(16) O1-Fe1-O2 100.92(16) O1 -Fe1-O2 78.10(15) O1 -Fe1-O2 163.76(16) O1-Fe1-O2 78.10(15) O1 -Fe1-O2 163.76(16) O1 -Fe1-O2 100.92(16) O2 -Fe1-O2 90.11(16) O1-Fe1-O2 163.76(16) O1 -Fe1-O2 100.92(16) O1 -Fe1-O2 78.10(15) O2 -Fe1-O2 90.11(16) O2-Fe1-O2 90.11(16) O2-Fe2-O1 81.74(15) O2-Fe2-O3 98.11(17) O1-Fe2-O3 96.04(18) O2-Fe2-O5 101.74(17) O1-Fe2-O5 174.49(18) O3-Fe2-O5 87.74(17) O2-Fe2-O4 97.95(17) O1-Fe2-O4 91.31(17) O3-Fe2-O4 163.14(18) O5-Fe2-O4 84.00(17) O1-Fe2-N1 79.41(18) O3-Fe2-N1 80.27(18) O5-Fe2-N1 97.34(19) O4-Fe2-N1 86.23(17) O2-Fe2-Fe1 42.26(12) O2-Fe3-O3 95.62(16) O2-Fe3-O7 96.10(17) O3 -Fe3-O7 90.50(16) O2-Fe3-O10 175.18(17) O3 -Fe3-O10 89.08(17) O7-Fe3-O10 84.85(16) O2-Fe3-O6 90.87(17) O3 -Fe3-O6 173.42(18) O7-Fe3-O6 87.79(18) O10-Fe3-O6 84.44(16) O2-Fe3-O8 91.53(16) O3 -Fe3-O8 95.73(16) O7-Fe3-O8 169.64(16) O10-Fe3-O8 86.98(15) O6-Fe3-O8 85.09(16) Fe2-O1-Fe1 96.98(16) Fe3-O2-Fe2 119.8(2) Fe3-O2-Fe1 134.8(2) Fe2-O2-Fe1 98.99(17) Fe3 -O3-Fe2 127.9(2)

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200 Table A-10. Selected interatomic distances () and angles () for (HNEt3)[Mn7(mda)6(Cl)6]MeCNEt2O (10MeCNEt2O) Mn1-O3 2.172(6) Mn2-O8 2.128(6) Mn1-O4 2.177(5) Mn2-O9 2.162(6) Mn1-O2 2.196(5) Mn2-O3 2.192(5) Mn1-O6 2.224(5) Mn2-N1 2.291(7) Mn1-O5 2.238(6) Mn2-O6 2.306(6) Mn1-O1 2.258(5) Mn2-Cl1 2.437(3) Mn3-O7 1.879(6) Mn4-O12 2.112(5) Mn3-O8 1.905(6) Mn4-O7 2.154(5) Mn3-O6 2.037(5) Mn4-O2 2.184(6) Mn3-N2 2.171(7) Mn4-O5 2.280(5) Mn3-O2 2.223(5) Mn4-N3 2.290(7) Mn3-Cl2 2.423(2) Mn4-Cl3 2.499(2) Mn5-O11 1.876(6) Mn6-O10 2.099(6) Mn5-O12 1.899(5) Mn6-O11 2.150(6) Mn5-O5 2.085(5) Mn6-O4 2.203(5) Mn5-O4 2.146(6) Mn6-N5 2.292(7) Mn5-N4 2.233(7) Mn6-O1 2.340(6) Mn5-Cl4 2.412(3) Mn6-Cl5 2.424(3) Mn7-O10 1.886(5) Mn7-O9 1.901(6) Mn7-O1 2.039(6) Mn7-O3 2.200(5) Mn7-N6 2.187(8) Mn7-Cl6 2.462(3) O3-Mn1-O4 99.0(2) O3-Mn1-O2 98.2(2) O4-Mn1-O2 97.66(19) O3-Mn1-O6 84.1(2) O4-Mn1-O6 176.5(2) O2-Mn1-O6 80.16(18) O3-Mn1-O5 176.8(2 O4-Mn1-O5 78.8(2) O2-Mn1-O5 84.4(2) O6-Mn1-O5 98.1(2) O3-Mn1-O1 79.7(2) O4-Mn1-O1 84.22(19) O2-Mn1-O1 177.4(2) O6-Mn1-O1 98.04(19) O5-Mn1-O1 97.8(2) O8-Mn2-O9 163.4(2) O8-Mn2-O3 97.4(2) O9-Mn2-O3 72.9(2) O8-Mn2-N1 106.6(2) O9-Mn2-N1 75.8(2) O3-Mn2-N1 141.2(2) O8-Mn2-O6 70.5(2) O9-Mn2-O6 94.4(2) O3-Mn2-O6 81.7(2) N1-Mn2-O6 78.2(2) O8-Mn2-Cl1 92.30(18) O9-Mn2-Cl1 103.76(19) O3-Mn2-Cl1 111.74(17) N1-Mn2-Cl1 97.6(2) O6-Mn2-Cl1 159.82(15) O7-Mn3-O8 170.9(2) O7-Mn3-O6 99.0(2) O8-Mn3-O6 81.0(2) O7-Mn3-N2 96.8(3) O8-Mn3-N2 80.3(3) O6-Mn3-N2 154.7(2) O7-Mn3-O2 77.9(2) O8-Mn3-O2 93.1(2) O6-Mn3-O2 83.72(19) N2-Mn3-O2 80.5(2) O7-Mn3-Cl2 92.69(18) O8-Mn3-Cl2 96.10(18) O6-Mn3-Cl2 104.35(15) N2-Mn3-Cl2 94.46(19)

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201 O2-Mn3-Cl2 168.56(16) O12-Mn4-O7 164.7(2) O12-Mn4-O2 98.1(2) O7-Mn4-O2 73.4(2) O12-Mn4-O5 71.21(19) O7-Mn4-O5 94.94(19) O2-Mn4-O5 83.7(2) O12-Mn4-N3 105.7(2) O7-Mn4-N3 76.9(2) O2-Mn4-N3 143.9(2) O5-Mn4-N3 78.9(2) O12-Mn4-Cl3 93.94(15) O7-Mn4-Cl3 100.84(16) O2-Mn4-Cl3 110.06(15) O5-Mn4-Cl3 161.46(16) N3-Mn4-Cl3 95.1(2) O11-Mn5-O12 172.6(3) O11-Mn5-O5 98.1(2) O12-Mn5-O5 79.8(2) O11-Mn5-O4 78.5(2) O12-Mn5-O4 94.2(2) O5-Mn5-O4 83.0(2) O11-Mn5-N4 99.3(2) O12-Mn5-N4 80.1(2) O5-Mn5-N4 151.9(2) O4-Mn5-N4 79.2(2) O11-Mn5-Cl4 91.5(2) O12-Mn5-Cl4 95.87(19) O5-Mn5-Cl4 107.04(17) O4-Mn5-Cl4 166.90(16) N4-Mn5-Cl4 94.3(2) O10-Mn6-O11 162.2(2) O10-Mn6-O4 97.7(2) O11-Mn6-O4 71.8(2) O10-Mn6-N5 105.7(3) O11-Mn6-N5 76.8(3) O4-Mn6-N5 140.8(3) O10-Mn6-O1 70.4(2) O11-Mn6-O1 93.4(2) O4-Mn6-O1 81.74(18) N5-Mn6-O1 77.3(2) O10-Mn6-Cl5 95.36(17) O11-Mn6-Cl5 101.87(16) O4-Mn6-Cl5 111.59(15) N5-Mn6-Cl5 97.2(2) O1-Mn6-Cl5 162.16(17) O10-Mn7-O9 171.4(3) O10-Mn7-O1 81.5(2) O9-Mn7-O1 98.1(3) O10-Mn7-N6 80.9(3) O9-Mn7-N6 96.7(3) O1-Mn7-N6 155.5(3) O10-Mn7-O3 93.5(2) O9-Mn7-O3 77.9(2) O1-Mn7-O3 84.0(2) N6-Mn7-O3 80.2(3) O10-Mn7-Cl6 94.69(19) O9-Mn7-Cl6 93.70(18) O1-Mn7-Cl6 105.32(17) N6-Mn7-Cl6 93.0(2)

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202 Table A-11. Selected interatomic distances () and angles () for {Na(HOMe)3[Mn7(mda)6(N3)6]}n (11) Mn1-O3 1.875(4) Mn2-O4 2.116(4) Mn1-O1 1.896(4) Mn2-N5 2.133(6) Mn1-N1 2.025(5) Mn2-O3 2.142(4) Mn1-O2 2.103(4) Mn2-O2 2.248(4) Mn1-O6 2.156(4) Mn2-O8 2.271(4) Mn1-N4 2.279(6) Mn2-N8 2.297(6) Mn3-O1 2.135(4) Mn3-N10 2.169(5) Mn3-O9 2.176(4) Mn3-O5 2.238(4) Mn3-O6 2.243(4) Mn3-N9 2.309(5) Mn4-O8 2.188(4) Mn4-O11 2.188(4) Mn4-O2 2.195(4) Mn4-O6 2.197(4) Mn4-O7 2.196(4) Mn4-O5 2.240(4) Mn5-O12 1.886(4) Mn5-O4 1.908(4) Mn5-N14 1.985(6) Mn5-O7 2.088(4) Mn5-O8 2.187(4) Mn5-N13 2.321(6) Mn6-O9 1.891(4) Mn6-O10 1.894(4) Mn6-N17 2.024(6) Mn6-O5 2.068(4) Mn6-O11 2.152(4) Mn6-N20 2.293(6) Mn7-O10 2.112(4) Mn7-N22 2.146(6) Mn7-O12 2.155(4) Mn7-O7 2.250(4) Mn7-O11 2.278(4) Mn7-N21 2.286(6) Na-O14 2.350(7) Na-O15 2.355(6) Na-N24 2.382(7) Na-O13 2.427(7) Na-N3 2.488(8) O3-Mn1-O1 177.44(19) O3-Mn1-N1 88.9(2) O1-Mn1-N1 93.5(2) O3-Mn1-O2 79.56(17) O1-Mn1-O2 98.06(18) N1-Mn1-O2 167.76(19) O3-Mn1-O6 99.37(18) O1-Mn1-O6 79.32(16) N1-Mn1-O6 104.0(2) O2-Mn1-O6 82.19(15) O3-Mn1-N4 101.1(2) O1-Mn1-N4 79.22(19) N1-Mn1-N4 99.8(2) O2-Mn1-N4 78.54(18) O6-Mn1-N4 148.69(19) O4-Mn2-N5 90.9(2) O4-Mn2-O3 169.96(17) N5-Mn2-O3 93.9(2) O4-Mn2-O2 99.07(16) N5-Mn2-O2 108.9(2) O3-Mn2-O2 71.01(15) O4-Mn2-O8 73.48(16) N5-Mn2-O8 162.1(2) O3-Mn2-O8 103.01(17) O2-Mn2-O8 82.76(14) O4-Mn2-N8 110.59(19) N5-Mn2-N8 99.7(2) O3-Mn2-N8 77.36(18) O2-Mn2-N8 138.19(17) O8-Mn2-N8 78.42(17) O1-Mn3-N10 88.66(19) O1-Mn3-O9 167.03(17) N10-Mn3-O9 96.64(19) O1-Mn3-O5 96.54(16) N10-Mn3-O5 115.0(2) O9-Mn3-O5 70.49(15) O1-Mn3-O6 72.60(16) N10-Mn3-O6 155.69(18)

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203 O9-Mn3-O6 105.01(16) O5-Mn3-O6 83.12(15) O1-Mn3-N9 113.45(18) N10-Mn3-N9 96.6(2) O9-Mn3-N9 77.80(18) O5-Mn3-N9 136.94(17) O6-Mn3-N9 77.70(17) O8-Mn4-O11 98.71(15) O8-Mn4-O2 85.94(15) O11-Mn4-O2 175.17(17) O8-Mn4-O7 77.90(15) O11-Mn4-O7 86.47(15) O2-Mn4-O7 95.85(15) O8-Mn4-O6 99.46(16) O11-Mn4-O6 98.65(15) O2-Mn4-O6 79.18(15) O7-Mn4-O6 174.58(16) O8-Mn4-O5 175.64(16) O11-Mn4-O5 78.19(15) O2-Mn4-O5 97.24(15) O7-Mn4-O5 98.75(15) O6-Mn4-O5 84.11(15) O12-Mn5-O4 178.52(19) O12-Mn5-N14 87.9(2) O4-Mn5-N14 93.5(2) O12-Mn5-O7 79.82(16) O4-Mn5-O7 98.70(17) N14-Mn5-O7 167.1(2) O12-Mn5-O8 100.34(18) O4-Mn5-O8 79.47(17) N14-Mn5-O8 106.0(2) O7-Mn5-O8 80.23(15) O12-Mn5-N13 101.05(19) O4-Mn5-N13 78.47(19) N14-Mn5-N13 100.4(2) O7-Mn5-N13 78.35(17) O8-Mn5-N13 146.34(18) O9-Mn6-O10 175.10(19) O9-Mn6-N17 94.5(2) O10-Mn6-N17 90.2(2) O9-Mn6-O5 79.98(17) O10-Mn6-O5 95.25(18) N17-Mn6-O5 174.1(2) O9-Mn6-O11 100.80(18) O10-Mn6-O11 79.54(17) O5-Mn6-O11 82.85(15) N17-Mn6-O11 100.3(2) O9-Mn6-N20 99.21(19) O10-Mn6-N20 78.81(18) N17-Mn6-N20 98.5(2) O5-Mn6-N20 80.50(17) O11-Mn6-N20 151.22(18) O10-Mn7-N22 90.0(2) O10-Mn7-O12 166.01(16) N22-Mn7-O12 94.3(2) O10-Mn7-O7 95.19(16) N22-Mn7-O7 110.6(2) O12-Mn7-O7 70.83(15) O10-Mn7-O11 72.41(16) N22-Mn7-O11 158.97(19) O12-Mn7-O11 105.49(16) O7-Mn7-O11 83.09(14) O10-Mn7-N21 114.89(18) N22-Mn7-N21 99.4(2) O12-Mn7-N21 77.53(17) O7-Mn7-N21 137.37(17) O11-Mn7-N21 78.55(17) N24-Na-N3 88.3(3) Mn1-O1-Mn3 110.37(19) Mn1-O2-Mn4 100.15(17) Mn1-O3-Mn2 110.4(2) Mn4-O2-Mn2 95.85(15) Mn5-O4-Mn2 110.8(2) Mn6-O5-Mn3 100.20(17) Mn6-O5-Mn4 99.91(16) Mn3-O5-Mn4 95.84(16) Mn1-O6-Mn4 98.46(16) Mn1-O6-Mn3 97.70(16) Mn4-O6-Mn3 96.91(16) Mn5-O7-Mn4 102.37(17) Mn5-O7-Mn7 99.20(16) Mn4-O7-Mn7 95.50(16) Mn5-O8-Mn4 99.47(17) Mn4-O8-Mn2 95.42(16) Mn5-O8-Mn2 96.05(16) Mn6-O9-Mn3 108.51(19) Mn6-O10-Mn7 111.3(2) Mn6-O11-Mn4 98.95(17) Mn6-O11-Mn7 96.66(17) Mn4-O11-Mn7 94.93(16)

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204 Table A-12. Selected interatomic distances () and angles () for [Mn18O11(OH)(N3)12(tea)3(teaH)3(OMe)(HOMe)]CH2Cl2Et2O (12CH2Cl2Et2O) Mn1-O32 1.928(4) Mn1-N4 1.953(4) Mn1-O4 1.930(3) Mn1-O16 1.963(3) Mn1-O1 2.229(3) Mn1-O10 2.345(3) Mn2-O4 1.896(3) Mn2-O11 1.929(3) Mn2-O6 2.019(3) Mn2-O9 2.163(3) Mn2-O10 2.238(3) Mn2-N7 2.249(4) Mn2-O8 2.295(3) Mn3-O4 1.891(3) Mn3-O2 1.929(3) Mn3-O3 1.939(3) Mn3-O5 2.114(3) Mn3-O1 2.210(3) Mn3-N8 2.364(4) Mn4-O9 1.878(3) Mn4-O6 1.918(3) Mn4-N9 1.957(4) Mn4-N12 1.979(4) Mn4-O2 2.122(4) Mn5-O20 1.839(3) Mn5-O32 1.949(4) Mn5-N15 1.969(5) Mn5-O16 2.025(3) Mn5-O23 2.210(3) Mn5-O26 2.326(3) Mn6-O8 1.899(3) Mn6-O21 1.915(3) Mn6-O23 1.915(3) Mn6-O10 1.970(3) Mn6-O16 2.110(3) Mn6-N23 2.304(4) Mn7-O5 1.870(3) Mn7-O26 1.922(3) Mn7-O16 1.960(3) Mn7-N18 2.130(4) Mn7-O18 2.134(3) Mn7-O1 2.166(3) Mn8-O22 1.839(3) Mn8-O11 1.936(3) Mn8-O8 1.957(3) Mn8-N36 1.981(4) Mn8-N26 2.326(4) Mn8-N23 2.358(4) Mn9-O6 1.875(3) Mn9-O19 1.921(3) Mn9-O8 1.940(3) Mn9-O7 1.955(3) Mn9-O5 2.157(3) Mn9-N26 2.417(4) Mn10-O13 1.873(3) Mn10-O3 1.893(3) Mn10-O17 1.918(3) Mn10-O5 1.926(3) Mn10-O7 2.243(3) Mn10-N18 2.520(4) Mn11-O20 1.869(3) Mn11-O24 1.937(3) Mn11-O25 1.979(3) Mn11-O21 1.995(3) Mn11-N22 2.400(4) Mn11-N42 2.451(4) Mn12-O20 2.111(3) Mn12-O27 2.179(3) Mn12-O28 2.228(3) Mn12-O18 2.235(3) Mn12-N21 2.296(4) Mn12-O26 2.369(3) Mn12-N42 2.379(4) Mn13-O22 1.864(3) Mn13-O25 1.948(3) Mn13-N39 1.960(5) Mn13-O21 1.989(3) Mn13-O30 2.281(3) Mn13-N23 2.429(4) Mn14-O18 1.895(3) Mn14-O19 1.944(3) Mn14-O30 1.957(3) Mn14-N42 1.997(4) Mn14-O21 2.212(3) Mn14-N33 2.346(4) Mn15-O27 1.876(3)

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205 Mn15-O17 1.915(3) Mn15-O18 1.920(3) Mn15-N30 1.995(4) Mn15-N33 2.330(4) Mn15-N18 2.448(4) Mn16-O22 2.096(3) Mn16-O31 2.157(3) Mn16-O29 2.262(4) Mn16-O19 2.276(3) Mn16-O30 2.319(3) Mn16-N45 2.351(4) Mn17-O14 1.884(3) Mn17-O31 1.905(3) Mn17-O17 1.930(3) Mn17-O19 1.965(3) Mn17-O7 2.316(3) Mn17-N33 2.371(4) Mn18-O13 2.201(3) Mn18-O12 2.216(3) Mn18-O14 2.248(3) Mn18-N30 2.254(4) Mn18-O15 2.280(4) Mn18-O17 2.290(3) Mn18-N29 2.315(4) O32-Mn1-O4 178.03(16) O32-Mn1-N4 86.78(17) O4-Mn1-N4 94.17(16) O32-Mn1-O16 79.03(14) O4-Mn1-O16 100.02(13) N4-Mn1-O16 165.81(17) O32-Mn1-O1 103.33(15) O4-Mn1-O1 78.14(13) N4-Mn1-O1 103.55(17) O16-Mn1-O1 79.93(13) O32-Mn1-O10 103.08(15) O4-Mn1-O10 74.99(13) N4-Mn1-O10 106.50(16) O16-Mn1-O10 77.13(12) O1-Mn1-O10 140.69(12) O4-Mn2-O11 172.55(14) O4-Mn2-O6 84.99(13) O11-Mn2-O6 97.63(14) O4-Mn2-O9 98.08(14) O11-Mn2-O9 89.36(14) O6-Mn2-O9 72.45(12) O4-Mn2-O10 78.31(13) O11-Mn2-O10 95.16(14) O6-Mn2-O10 136.80(12) O9-Mn2-O10 148.88(12) O4-Mn2-N7 102.57(14) O11-Mn2-N7 79.07(14) O6-Mn2-N7 146.63(14) O9-Mn2-N7 74.31(13) O10-Mn2-N7 76.37(13) O4-Mn2-O8 102.81(12) O11-Mn2-O8 71.47(12) O6-Mn2-O8 73.55(12) O9-Mn2-O8 137.98(12) O10-Mn2-O8 71.85(11) N7-Mn2-O8 133.80(13) O4-Mn3-O2 93.64(14) O4-Mn3-O3 172.69(14) O2-Mn3-O3 89.82(15) O4-Mn3-O5 98.04(13) O2-Mn3-O5 138.13(14) O3-Mn3-O5 75.17(13) O4-Mn3-O1 79.42(13) O2-Mn3-O1 146.19(14) O3-Mn3-O1 101.16(14) O5-Mn3-O1 75.66(12) O4-Mn3-N8 109.46(14) O2-Mn3-N8 76.81(15) O3-Mn3-N8 77.60(14) O5-Mn3-N8 134.36(14) O1-Mn3-N8 74.58(14) O9-Mn4-O6 81.34(13) O9-Mn4-N9 94.97(18) O6-Mn4-N9 172.01(19) O9-Mn4-N12 170.47(17) O6-Mn4-N12 92.14(16) N9-Mn4-N12 90.60(19) O9-Mn4-O2 90.41(15) O6-Mn4-O2 84.58(13) N9-Mn4-O2 102.59(18) N12-Mn4-O2 95.92(17) O20-Mn5-O32 176.80(14) O20-Mn5-N15 96.46(18) O32-Mn5-N15 86.73(19) O32-Mn5-O16 77.05(14) N15-Mn5-O16 160.76(19)

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206 O20-Mn5-O23 82.28(14) O32-Mn5-O23 96.21(15) O20-Mn5-O16 99.86(13) N15-Mn5-O23 113.44(19) O16-Mn5-O23 79.01(12) O20-Mn5-O26 80.75(13) O32-Mn5-O26 99.03(15) N15-Mn5-O26 99.63(19) O16-Mn5-O26 73.22(12) O23-Mn5-O26 144.22(12) O8-Mn6-O21 89.96(13) O8-Mn6-O23 177.65(14) O21-Mn6-O23 89.66(14) O8-Mn6-O10 86.84(13) O21-Mn6-O10 176.74(14) O23-Mn6-O10 93.51(14) O8-Mn6-O16 93.74(13) O21-Mn6-O16 96.72(12) O23-Mn6-O16 84.01(14) O10-Mn6-O16 82.88(13) O8-Mn6-N23 85.45(14) O21-Mn6-N23 84.11(14) O23-Mn6-N23 96.82(14) O10-Mn6-N23 96.25(14) O16-Mn6-N23 178.85(14) O5-Mn7-O26 176.87(14) O5-Mn7-O16 92.91(13) O26-Mn7-O16 84.30(14) O5-Mn7-N18 86.54(15) O26-Mn7-N18 96.26(15) O16-Mn7-N18 179.42(15) O5-Mn7-O18 90.28(13) O26-Mn7-O18 88.63(13) O16-Mn7-O18 96.51(12) N18-Mn7-O18 83.66(14) O5-Mn7-O1 81.83(13) O26-Mn7-O1 99.12(13) O16-Mn7-O1 81.57(13) N18-Mn7-O1 98.18(15) O18-Mn7-O1 171.75(12) O22-Mn8-O11 173.23(14) O22-Mn8-O8 94.18(13) O11-Mn8-O8 79.31(13) O22-Mn8-N36 96.51(16) O11-Mn8-N36 90.10(16) O8-Mn8-N36 168.91(16) O22-Mn8-N26 83.22(14) O11-Mn8-N26 94.31(14) O8-Mn8-N26 85.29(14) N36-Mn8-N26 98.89(17) O22-Mn8-N23 80.32(14) O11-Mn8-N23 100.51(14) O8-Mn8-N23 82.71(14) N36-Mn8-N23 96.16(16) N26-Mn8-N23 158.81(14) O6-Mn9-O19 176.96(13) O6-Mn9-O8 85.57(13) O19-Mn9-O8 95.21(13) O6-Mn9-O7 93.91(13) O19-Mn9-O7 85.20(12) O8-Mn9-O7 177.88(13) O6-Mn9-O5 85.97(13) O19-Mn9-O5 96.80(12) O8-Mn9-O5 98.70(12) O7-Mn9-O5 83.30(13) O6-Mn9-N26 87.68(14) O19-Mn9-N26 89.50(13) O8-Mn9-N26 83.19(13) O7-Mn9-N26 94.73(14) O5-Mn9-N26 173.21(13) O13-Mn10-O3 95.49(14) O13-Mn10-O17 87.11(13) O3-Mn10-O17 173.00(15) O13-Mn10-O5 176.32(14) O3-Mn10-O5 80.83(13) O17-Mn10-O5 96.54(13) O13-Mn10-O7 99.56(13) O3-Mn10-O7 106.46(13) O17-Mn10-O7 79.44(12) O5-Mn10-O7 81.69(12) O13-Mn10-N18 105.50(15) O3-Mn10-N18 97.77(15) O17-Mn10-N18 75.25(13) O5-Mn10-N18 75.04(14) O7-Mn10-N18 143.07(13) O20-Mn11-O24 90.51(15) O20-Mn11-O25 171.98(14) O24-Mn11-O25 96.03(15) O20-Mn11-O21 95.15(13) O24-Mn11-O21 157.74(14) O25-Mn11-O21 77.06(13) O20-Mn11-N22 108.15(14)

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207 O24-Mn11-N22 77.36(14) O25-Mn11-N22 77.91(14) O21-Mn11-N22 120.71(14) O20-Mn11-N42 81.62(13) O24-Mn11-N42 81.88(13) O25-Mn11-N42 94.70(14) O21-Mn11-N42 77.69(12) N22-Mn11-N42 157.01(14) O20-Mn12-O28 85.97(13) O27-Mn12-O28 103.83(13) O20-Mn12-O18 94.53(12) O27-Mn12-O18 71.65(11) O28-Mn12-O18 149.74(13) O20-Mn12-N21 115.65(13) O27-Mn12-N21 77.39(13) O28-Mn12-N21 76.43(14) O18-Mn12-N21 128.91(14) O20-Mn12-O26 74.62(12) O27-Mn12-O26 104.96(12) O28-Mn12-O26 132.47(12) O18-Mn12-O26 76.04(11) N21-Mn12-O26 74.01(13) O20-Mn12-N42 78.80(13) O27-Mn12-N42 92.35(13) O28-Mn12-N42 80.00(13) O18-Mn12-N42 70.50(12) N21-Mn12-N42 151.05(14) O26-Mn12-N42 134.93(12) O22-Mn13-O25 175.99(14) O22-Mn13-N39 92.97(16) O25-Mn13-N39 88.94(17) O22-Mn13-O21 100.43(13) O25-Mn13-O21 77.91(14) N39-Mn13-O21 166.13(16) O22-Mn13-O30 79.18(13) O25-Mn13-O30 96.90(13) N39-Mn13-O30 106.13(16) O21-Mn13-O30 80.11(12) O22-Mn13-N23 77.95(13) O25-Mn13-N23 105.19(14) N39-Mn13-N23 100.22(17) O21-Mn13-N23 79.35(13) O30-Mn13-N23 145.74(13) O18-Mn14-O19 93.51(13) O18-Mn14-O30 178.40(13) O19-Mn14-O30 87.59(13) O18-Mn14-N42 86.40(15) O19-Mn14-N42 176.47(14) O30-Mn14-N42 92.43(15) O18-Mn14-O21 98.39(12) O19-Mn14-O21 99.85(12) O30-Mn14-O21 82.54(12) N42-Mn14-O21 83.65(13) O18-Mn14-N33 84.14(13) O19-Mn14-N33 81.92(12) O30-Mn14-N33 94.88(13) N42-Mn14-N33 94.56(14) O21-Mn14-N33 176.78(13) O27-Mn15-O17 178.41(14) O27-Mn15-O18 85.78(13) O17-Mn15-O18 93.24(13) O27-Mn15-N30 97.44(15) O17-Mn15-N30 83.60(15) O18-Mn15-N30 175.52(16) O27-Mn15-N33 101.46(14) O17-Mn15-N33 79.67(13) O18-Mn15-N33 84.05(14) N30-Mn15-N33 92.24(16) O27-Mn15-N18 101.48(15) O17-Mn15-N18 77.10(14) O18-Mn15-N18 80.23(14) N30-Mn15-N18 102.08(17) N33-Mn15-N18 151.02(14) O22-Mn16-O31 161.14(12) O22-Mn16-O29 90.73(13) O31-Mn16-O29 102.50(13) O22-Mn16-O19 90.67(11) O31-Mn16-O19 72.01(11) O29-Mn16-O19 157.84(12) O22-Mn16-O30 73.93(11) O31-Mn16-O30 106.44(12) O29-Mn16-O30 129.46(12) O19-Mn16-O30 71.95(11) O22-Mn16-N45 120.10(13) O31-Mn16-N45 77.13(13) O29-Mn16-N45 73.10(13) O19-Mn16-N45 124.41(12) O30-Mn16-N45 74.16(12) O14-Mn17-O31 96.41(14) O14-Mn17-O17 85.16(13) O31-Mn17-O17 177.56(13) O14-Mn17-O19 178.87(14)

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208 O31-Mn17-O19 84.72(13) O17-Mn17-O19 93.71(12) O14-Mn17-O7 104.68(13) O31-Mn17-O7 103.99(12) O17-Mn17-O7 77.35(12) O19-Mn17-O7 75.09(12) O14-Mn17-N33 98.88(13) O31-Mn17-N33 99.56(14) O17-Mn17-N33 78.32(13) O19-Mn17-N33 80.83(13) O7-Mn17-N33 144.28(12) O13-Mn18-O12 137.57(13) O13-Mn18-O14 102.13(12) O12-Mn18-O14 101.19(13) O13-Mn18-N30 122.87(14) O12-Mn18-N30 86.03(13) O14-Mn18-N30 101.34(14) O13-Mn18-O15 74.09(14) O12-Mn18-O15 80.07(15) O14-Mn18-O15 175.04(14) N30-Mn18-O15 83.50(16) O13-Mn18-O17 71.10(11) O12-Mn18-O17 151.06(12) O14-Mn18-O17 69.30(11) N30-Mn18-O17 70.01(12) O15-Mn18-O17 111.83(15) O13-Mn18-N29 75.45(13) O12-Mn18-N29 76.81(13) O14-Mn18-N29 75.46(14) N30-Mn18-N29 161.41(15) O15-Mn18-N29 100.29(16) O17-Mn18-N29 123.82(13) Mn7-O1-Mn3 94.73(12) Mn7-O1-Mn1 91.60(13) Mn3-O1-Mn1 90.39(12) Mn3-O2-Mn4 107.59(15) Mn10-O3-Mn3 105.17(16) Mn3-O4-Mn2 114.94(16) Mn3-O4-Mn1 111.00(15) Mn2-O4-Mn1 115.72(16) Mn7-O5-Mn10 112.86(15) Mn7-O5-Mn3 107.64(14) Mn10-O5-Mn3 97.64(13) Mn7-O5-Mn9 130.82(16) Mn10-O5-Mn9 99.10(13) Mn3-O5-Mn9 103.76(13) Mn9-O6-Mn4 147.55(18) Mn9-O6-Mn2 105.83(15) Mn4-O6-Mn2 104.69(13) Mn9-O7-Mn10 95.40(13) Mn9-O7-Mn17 93.17(12) Mn10-O7-Mn17 89.75(11) Mn6-O8-Mn9 138.92(17) Mn6-O8-Mn8 107.90(15) Mn9-O8-Mn8 108.02(14) Mn6-O8-Mn2 100.51(13) Mn9-O8-Mn2 94.06(13) Mn8-O8-Mn2 97.30(12) Mn4-O9-Mn2 100.78(14) Mn6-O10-Mn2 100.28(13) Mn6-O10-Mn1 95.78(13) Mn2-O10-Mn1 89.92(12) Mn2-O11-Mn8 111.81(15) Mn10-O13-Mn18 102.85(15) Mn17-O14-Mn18 104.28(14) Mn7-O16-Mn1 106.88(15) Mn1-O16-Mn5 99.90(14) Mn7-O16-Mn6 136.91(16) Mn1-O16-Mn6 104.06(13) Mn5-O16-Mn6 97.51(14) Mn15-O17-Mn10 121.59(16) Mn15-O17-Mn17 114.23(15) Mn10-O17-Mn17 113.45(15) Mn15-O17-Mn18 103.52(13) Mn10-O17-Mn18 98.28(12) Mn17-O17-Mn18 101.23(13) Mn14-O18-Mn15 108.70(15) Mn14-O18-Mn7 134.80(16) Mn15-O18-Mn7 106.07(14) Mn14-O18-Mn12 105.09(14) Mn15-O18-Mn12 99.31(13) Mn7-O18-Mn12 96.73(12) Mn9-O19-Mn14 128.40(15) Mn9-O19-Mn17 106.43(14) Mn14-O19-Mn17 110.62(14) Mn9-O19-Mn16 107.54(13) Mn14-O19-Mn16 101.17(13) Mn17-O19-Mn16 98.48(12) Mn5-O20-Mn11 122.86(17) Mn5-O20-Mn12 114.48(16) Mn11-O20-Mn12 112.67(15) Mn6-O21-Mn13 110.02(14)

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209 Mn6-O21-Mn11 111.36(14) Mn13-O21-Mn11 101.49(14) Mn6-O21-Mn14 128.25(16) Mn8-O22-Mn16 118.02(16) Mn13-O21-Mn14 99.03(13) Mn13-O22-Mn16 114.11(15) Mn11-O21-Mn14 103.17(13) Mn6-O23-Mn5 97.56(14) Mn8-O22-Mn13 116.65(16) Mn13-O25-Mn11 103.54(16) Mn7-O26-Mn5 96.40(13) Mn7-O26-Mn12 98.56(13) Mn5-O26-Mn12 90.15(12) Mn14-O30-Mn13 97.72(12) Mn15-O27-Mn12 102.73(14) Mn14-O30-Mn16 99.28(13) Mn13-O30-Mn16 92.57(11) Mn17-O31-Mn16 104.67(14)

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210 Table A-13. Selected interatomic distances () and angles () for [Mn31O20(N3)4(O2CMe)23(tea)2(dea)2(OMe)7(MeOH)]n26MeCN (136MeCN) Mn1-O30 1.813(8) Mn1-O3 1.912(10) Mn1-O2 1.895(7) Mn1-O1 1.968(8) Mn1-O4 2.187(8) Mn2-O4 1.908(9) Mn2-O7 1.952(7) Mn2-O6 1.958(9) Mn2-N1 1.959(11) Mn2-O8 2.124(9) Mn2-O3 2.326(9) Mn3-O3 2.159(8) Mn3-O2 2.190(9) Mn3-O10 2.201(8) Mn3-N4 2.262(13) Mn3-O5 2.263(8) Mn3-O7 2.340(8) Mn3-O11 2.373(8) Mn4-O17 1.886(8) Mn4-O7 1.894(8) Mn4-O18 1.916(11) Mn4-O6 1.957(9) Mn4-O9 2.134(10) Mn4-O10 2.371(8) Mn5-O21 1.845(8) Mn5-O19 1.935(11) Mn5-O10 1.943(8) Mn5-O11 1.982(8) Mn5-O13 2.239(8) Mn5-O17 2.401(8) Mn6-O7 1.891(8) Mn6-O12 1.895(8) Mn6-O17 1.915(9) Mn6-O16 1.921(7) Mn6-O15 2.208(9) Mn6-O11 2.341(7) Mn7-O2 1.852(8) Mn7-O11 1.957(8) Mn7-O12 1.960(7) Mn7-O16 2.014(8) Mn7-O21 2.037(9) Mn8-O13 1.877(9) Mn8-O5 1.931(8) Mn8-O16 1.934(9) Mn8-O12 1.956(8) Mn8-O14 2.123(9) Mn8-O11 2.287(7) Mn9-O23 2.116(9) Mn9-O16 2.129(7) Mn9-O25 2.129(9) Mn9-O24 2.204(9) Mn9-O5 2.225(9) Mn9-O2 2.256(8) Mn10-O21 1.876(8) Mn10-O31 1.917(7) Mn10-O25 1.949(8) Mn10-O27 1.988(9) Mn10-O30 2.204(8) Mn10-O26 2.367(10) Mn11-O17 2.121(8) Mn11-O22 2.144(9) Mn11-O20 2.152(11) Mn11-O26 2.226(10) Mn11-O25 2.269(8) Mn11-O28 2.283(9) Mn12-O30 1.862(7) Mn12-O38 1.940(7) Mn12-O31 1.967(8) Mn12-O36 1.976(9) Mn12-O33 2.092(11) Mn12-O35 2.429(9) Mn13-O29 1.873(11) Mn13-O25 1.880(7) Mn13-O31 1.934(8) Mn13-O34 1.970(8) Mn13-O28 2.157(10) Mn14-N11 2.060(16) Mn14-O39 2.120(10) Mn14-O32 2.139(10) Mn14-O31 2.200(8) Mn14-O34 2.230(10) Mn14-O38 2.291(9) Mn15-N6 2.070(15) Mn15-O37 2.114(11) Mn15-O40 2.216(11) Mn15-O38 2.221(9)

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211 Mn15-O34 2.221(9) Mn15-O35 2.257(9) Mn16-O42 2.125(12) Mn16-O41 2.185(12) Mn16-O43 2.216(12) Mn16-O40 2.221(13) Mn16-O45 2.242(12) Mn16-N6 2.275(13) Mn17-O84 2.109(11) Mn17-O44 2.131(12) Mn17-O47 2.201(10) Mn17-O53 2.241(10) Mn17-O45 2.252(10) Mn17-O49 2.312(9) Mn18-N9 2.052(13) Mn18-O52 2.112(10) Mn18-O46 2.140(11) Mn18-O51 2.217(8) Mn18-O47 2.245(10) Mn18-O53 2.269(10) Mn19-O58 1.863(8) Mn19-O51 1.910(9) Mn19-O47 1.921(8) Mn19-O48 1.940(11) Mn19-O50 2.194(11) Mn19-O49 2.504(11) Mn20-O59 1.839(8) Mn20-O60 1.929(9) Mn20-O53 1.937(8) Mn20-O51 1.967(9) Mn20-O65 2.076(10) Mn20-O49 2.405(11) Mn21-O67 2.105(8) Mn21-O57 2.160(10) Mn21-O61 2.168(12) Mn21-O63 2.207(10) Mn21-O58 2.248(9) Mn21-O50 2.280(9) Mn22-O68 1.869(8) Mn22-O51 1.924(8) Mn22-O58 1.950(8) Mn22-O64 1.993(9) Mn22-O59 2.172(9) Mn22-O63 2.303(10) Mn23-O71 2.120(8) Mn23-O54 2.128(10) Mn23-O58 2.144(9) Mn23-O55 2.175(10) Mn23-O70 2.260(9) Mn23-O69 2.265(8) Mn24-O59 1.859(9) Mn24-O69 1.912(8) Mn24-O56 1.934(9) Mn24-O76 1.989(9) Mn24-O75 2.199(9) Mn25-O76 2.166(9) Mn25-O77 2.185(9) Mn25-O69 2.211(8) Mn25-N13 2.247(15) Mn25-O70 2.286(9) Mn25-O80 2.352(9) Mn25-O73 2.379(9) Mn26-O69 1.817(9) Mn26-O73 1.941(9) Mn26-O74 1.941(8) Mn26-O68 2.021(8) Mn26-O71 2.026(8) Mn27-O68 1.845(8) Mn27-O7 1.945(9) Mn27-O66 1.970(9) Mn27-O73 1.993(8) Mn27-O72 2.230(9) Mn27-O67 2.441(8) Mn28-O74 1.906(9) Mn28-O71 1.911(9) Mn28-O72 1.933(9) Mn28-O70 1.948(10) Mn28-O82 2.125(9) Mn28-O73 2.278(8) Mn29-O80 1.867(10) Mn29-O67 1.910(8) Mn29-O71 1.927(8) Mn29-O74 1.934(8) Mn29-O81 2.208(10) Mn29-O73 2.345(8) Mn30-O67 1.899(9) Mn30-O80 1.912(9) Mn30-O62 1.943(10) Mn30-O78 1.947(9) Mn30-O83 2.203(10) Mn30-O77 2.352(9) Mn31-O75 1.924(9)

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212 Mn31-O80 1.961(9) Mn31-N16 1.967(15) Mn31-O78 1.982(9) Mn31-O79 2.155(10) Mn31-O76 2.309(9) O30 -Mn1-O2 93.8(3) O30 -Mn1-O3 175.5(3) O2-Mn1-O3 84.6(4) O30 -Mn1-O1 95.9(4) O2-Mn1-O1 162.8(4) O3-Mn1-O1 84.6(4) O30 -Mn1-O4 104.4(3) O2-Mn1-O4 97.2(3) O3-Mn1-O4 80.0(3) O1 -Mn1-O4 94.0(3) O4-Mn2-O7 92.4(3) O4-Mn2-O6 166.2(3) O7-Mn2-O6 76.8(3) O4-Mn2-N1 97.8(4) O7-Mn2-N1 166.3(5) O6-Mn2-N1 91.7(4) O4-Mn2-O8 96.3(4) O7-Mn2-O8 94.3(3) O6-Mn2-O8 93.0(4) N1-Mn2-O8 93.7(4) O4-Mn2-O3 76.6(3) O7-Mn2-O3 83.1(3) O6-Mn2-O3 93.4(4) N1-Mn2-O3 90.3(4) O8-Mn2-O3 172.3(4) O3-Mn3-O2 72.2(3) O3-Mn3-O10 122.1(3) O2-Mn3-O10 155.0(3) O3-Mn3-N4 79.6(4) O2-Mn3-N4 129.2(4) O10-Mn3-N4 75.6(4) O3-Mn3-O5 113.5(3) O2-Mn3-O5 78.0(3) O10-Mn3-O5 109.8(3) N4-Mn3-O5 75.9(4) O3-Mn3-O7 78.6(3) O2-Mn3-O7 88.1(3) O10-Mn3-O7 76.1(3) N4-Mn3-O7 126.6(4) O5-Mn3-O7 157.0(3) O3-Mn3-O11 145.6(3) O2-Mn3-O11 84.1(3) O10-Mn3-O11 73.4(3) N4-Mn3-O11 134.6(3) O5-Mn3-O11 84.4(3) O7-Mn3-O11 76.0(3) O17-Mn4-O7 83.8(4) O17-Mn4-O18 101.2(4) O7-Mn4-O18 168.7(4) O17-Mn4-O6 161.5(4) O7-Mn4-O6 78.2(4) O18-Mn4-O6 95.9(4) O17-Mn4-O9 96.6(4) O7-Mn4-O9 98.9(4) O18-Mn4-O9 90.6(4) O6-Mn4-O9 90.1(4) O17-Mn4-O10 79.9(3) O7-Mn4-O10 81.3(3) O18-Mn4-O10 89.6(4) O6-Mn4-O10 93.4(3) O9-Mn4-O10 176.5(3) O21-Mn5-O19 95.7(4) O21-Mn5-O10 171.1(4) O19-Mn5-O10 89.9(4) O21-Mn5-O11 86.6(3) O19-Mn5-O11 175.2(4) O10-Mn5-O11 88.4(3) O21-Mn5-O13 90.8(3) O19-Mn5-O13 97.3(4) O10-Mn5-O13 95.4(3) O11-Mn5-O13 78.4(3) O21-Mn5-O17 93.9(3) O19-Mn5-O17 103.9(3) O10-Mn5-O17 78.1(3) O11-Mn5-O17 80.1(3) O13 -Mn5-O17 157.7(3) O7-Mn6-O12 94.5(3) O7-Mn6-O17 83.1(3) O12-Mn6-O17 171.6(3) O7-Mn6-O16 165.0(3) O12-Mn6-O16 83.3(3) O17-Mn6-O16 97.0(3) O7-Mn6-O15 106.0(3) O12-Mn6-O15 95.7(3)

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213 O17-Mn6-O15 92.7(4) O16-Mn6-O15 88.9(3) O7-Mn6-O11 85.9(3) O12-Mn6-O11 88.7(3) O17-Mn6-O11 83.1(3) O16-Mn6-O11 79.2(3) O15-Mn6-O11 166.8(3) O2 -Mn7-O11 172.7(3) O2 -Mn7-O12 97.5(3) O11-Mn7-O12 88.3(3) O2 -Mn7-O16 85.8(3) O11-Mn7-O16 87.1(3) O12 -Mn7-O16 158.0(3) O2 -Mn7-O21 101.1(3) O11-Mn7-O21 82.2(3) O12 -Mn7-O21 99.7(3) O16-Mn7-O21 101.0(3) O13-Mn8-O5 96.0(4) O13-Mn8-O16 167.3(3) O5 -Mn8-O16 84.0(4) O13-Mn8-O12 97.1(3) O5 -Mn8-O12 164.5(4) O16-Mn8-O12 81.4(3) O13-Mn8-O14 93.1(4) O5 -Mn8-O14 94.5(3) O16-Mn8-O14 99.6(4) O12-Mn8-O14 93.0(3) O13-Mn8-O11 79.3(3) O5 -Mn8-O11 94.8(3) O16-Mn8-O11 88.0(3) O12-Mn8-O11 79.6(3) O14-Mn8-O11 168.5(3) O23-Mn9-O16 110.7(3) O23-Mn9-O25 92.3(4) O16-Mn9-O25 89.2(3) O23-Mn9-O24 90.6(3) O16-Mn9-O24 155.1(3) O25-Mn9-O24 103.2(3) O23-Mn9-O5 90.8(4) O16-Mn9-O5 72.8(3) O25-Mn9-O5 161.6(3) O24-Mn9-O5 94.8(3) O23-Mn9-O2 165.7(4) O16-Mn9-O2 73.8(3) O25-Mn9-O2 101.5(3) O24-Mn9-O2 82.5(3) O5 -Mn9-O2 77.4(3) O21-Mn10-O31 177.1(4) O21-Mn10-O25 94.9(3) O31-Mn10-O25 82.3(3) O21-Mn10-O27 93.8(4) O31-Mn10-O27 89.2(3) O25-Mn10-O27 164.4(3) O21-Mn10-O30 98.2(3) O31-Mn10-O30 81.7(3) O25-Mn10-O30 99.4(3) O27-Mn10-O30 92.2(3) O21-Mn10-O26 86.0(3) O31-Mn10-O26 94.5(3) O25-Mn10-O26 86.5(3) O27-Mn10-O26 81.2(4) O30-Mn10-O26 172.4(3) O17-Mn11-O22 94.8(3) O17-Mn11-O20 90.2(4) O22-Mn11-O20 92.4(4) O17-Mn11-O26 96.6(3) O22-Mn11-O26 168.3(3) O20-Mn11-O26 84.7(4) O17-Mn11-O25 100.2(3) O22-Mn11-O25 98.1(3) O20-Mn11-O25 164.6(3) O26-Mn11-O25 82.8(3) O17-Mn11-O28 175.0(3) O22-Mn11-O28 88.4(3) O20-Mn11-O28 93.5(4) O26-Mn11-O28 80.5(4) O25-Mn11-O28 75.6(3) O30-Mn12-O38 171.8(3) O30-Mn12-O31 89.8(3) O38-Mn12-O31 84.3(3) O30-Mn12-O36 95.5(4) O38-Mn12-O36 89.7(4) O31-Mn12-O36 170.6(4) O30-Mn12-O33 92.7(3) O38-Mn12-O33 93.0(4) O31-Mn12-O33 90.0(4) O36-Mn12-O33 97.6(4) O30-Mn12-O35 91.8(3) O38-Mn12-O35 81.9(3) O31-Mn12-O35 82.4(3) O36-Mn12-O35 89.6(4) O33-Mn12-O35 171.1(3)

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214 O29-Mn13-O25 97.7(4) O29-Mn13-O31 168.6(4) O25-Mn13-O31 83.6(3) O29-Mn13-O34 92.3(4) O25-Mn13-O34 169.7(4) O31-Mn13-O34 86.1(4) O29-Mn13-O28 93.1(4) O25-Mn13-O28 87.1(3) O31-Mn13-O28 98.3(4) O34-Mn13-O28 94.8(4) N11 -Mn14-O39 98.5(5) N11 -Mn14-O32 90.6(5) O39-Mn14-O32 101.7(4) N11 -Mn14-O31 100.8(4) O39-Mn14-O31 155.9(4) O32-Mn14-O31 92.4(3) N11 -Mn14-O34 173.0(4) O39-Mn14-O34 87.8(4) O32-Mn14-O34 85.0(4) O31-Mn14-O34 74.0(3) N11 -Mn14-O38 101.9(4) O39-Mn14-O38 90.6(3) O32-Mn14-O38 161.1(3) O31-Mn14-O38 71.4(3) O34-Mn14-O38 81.1(3) N6-Mn15-O37 90.3(5) N6-Mn15-O40 81.0(5) O37-Mn15-O40 94.5(4) N6-Mn15-O38 173.0(4) O37-Mn15-O38 89.2(4) O40-Mn15-O38 92.1(4) N6-Mn15-O34 98.2(5) O37-Mn15-O34 170.8(4) O40-Mn15-O34 90.5(4) O38-Mn15-O34 82.9(3) N6-Mn15-O35 106.7(5) O37-Mn15-O35 95.9(4) O40-Mn15-O35 166.9(4) O38-Mn15-O35 80.3(3) O34-Mn15-O35 78.2(3) O42-Mn16-O41 95.0(5) O42-Mn16-O43 86.7(5) O41-Mn16-O43 168.7(5) O42-Mn16-O40 93.0(5) O41-Mn16-O40 81.8(5) O43-Mn16-O40 87.0(5) O42-Mn16-O45 94.4(4) O41-Mn16-O45 96.8(5) O43-Mn16-O45 94.2(4) O40-Mn16-O45 172.6(4) O42-Mn16-N6 169.0(5) O41-Mn16-N6 86.9(5) O43-Mn16-N6 89.3(5) O40-Mn16-N6 76.5(5) O45-Mn16-N6 96.2(5) O84-Mn17-O44 94.4(5) O84-Mn17-O47 167.4(4) O44-Mn17-O47 90.1(5) O84-Mn17-O53 91.0(4) O44-Mn17-O53 163.8(4) O47-Mn17-O53 81.6(3) O84-Mn17-O45 99.6(4) O44-Mn17-O45 101.0(4) O47-Mn17-O45 91.0(4) O53-Mn17-O45 93.1(4) O84-Mn17-O49 92.7(4) O44-Mn17-O49 86.6(4) O47-Mn17-O49 75.9(3) O53-Mn17-O49 77.9(3) O45-Mn17-O49 164.9(4) N9-Mn18-O52 92.6(5) N9-Mn18-O52 92.6(5) O52-Mn18-O46 103.5(4) N9-Mn18-O51 100.9(4) O52-Mn18-O51 93.0(3) O46-Mn18-O51 153.6(5) N9-Mn18-O47 172.6(4) O52-Mn18-O47 84.8(4) O46-Mn18-O47 88.4(4) O51-Mn18-O47 72.4(3) N9-Mn18-O53 100.9(5) O52-Mn18-O53 160.5(4) O46-Mn18-O53 88.5(4) O51-Mn18-O53 70.8(3) O47-Mn18-O53 80.1(3) O58-Mn19-O51 83.9(4) O58-Mn19-O47 170.8(4) O51-Mn19-O47 87.0(4) O58-Mn19-O48 97.4(4) O51-Mn19-O48 170.8(5) O47-Mn19-O48 91.8(4) O58-Mn19-O50 87.3(4)

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215 O51-Mn19-O50 97.1(4) O47-Mn19-O50 92.7(4) O48-Mn19-O50 92.1(5) O58-Mn19-O49 102.8(3) O51-Mn19-O49 78.9(4) O47-Mn19-O49 76.5(4) O48-Mn19-O49 91.9(4) O50-Mn19-O49 168.5(3) O59-Mn20-O60 97.4(4) O59-Mn20-O53 170.5(4) O60-Mn20-O53 89.8(4) O59-Mn20-O51 88.8(3) O60-Mn20-O51 170.8(4) O53-Mn20-O51 83.4(4) O59-Mn20-O65 91.1(4) O60-Mn20-O65 95.9(4) O53-Mn20-O65 94.5(4) O51-Mn20-O65 90.8(4) O59-Mn20-O49 91.7(4) O60-Mn20-O49 92.5(4) O53-Mn20-O49 81.7(4) O51-Mn20-O49 80.4(4) O65-Mn20-O49 170.7(4) O67-Mn21-O57 94.6(3) O67-Mn21-O61 91.2(4) O57-Mn21-O61 92.2(4) O67-Mn21-O63 96.4(4) O57-Mn21-O63 168.7(4) O61-Mn21-O63 84.9(4) O67-Mn21-O58 99.6(3) O57-Mn21-O58 100.2(4) O61-Mn21-O58 162.7(4) O63-Mn21-O58 80.6(4) O67-Mn21-O50 174.6(3) O57-Mn21-O50 90.0(4) O61-Mn21-O50 91.4(4) O63-Mn21-O50 79.1(4) O58-Mn21-O50 76.8(3) O68-Mn22-O51 176.0(4) O68-Mn22-O58 95.0(3) O51-Mn22-O58 81.2(4) O68-Mn22-O64 94.0(4) O51-Mn22-O64 90.0(4) O58-Mn22-O64 164.7(4) O68-Mn22-O59 98.8(3) O51-Mn22-O59 80.9(3) O58-Mn22-O59 100.0(4) O64-Mn22-O59 90.8(4) O68-Mn22-O63 86.6(4) O51-Mn22-O63 94.1(4) O58-Mn22-O63 84.9(4) O64-Mn22-O63 83.3(4) O59-Mn22-O63 172.3(3) O71-Mn23-O54 109.3(4) O71-Mn23-O58 89.7(3) O54-Mn23-O58 91.5(4) O71-Mn23-O55 153.6(3) O54-Mn23-O55 92.6(4) O58-Mn23-O55 104.7(3) O71-Mn23-O70 72.7(4) O54-Mn23-O70 90.1(4) O58-Mn23-O70 161.8(3) O55-Mn23-O70 93.3(3) O71-Mn23-O69 73.2(3) O54-Mn23-O69 166.6(4) O58-Mn23-O69 101.7(3) O55-Mn23-O69 82.2(3) O70-Mn23-O69 78.0(3) O59-Mn24-O69 92.6(4) O59-Mn24-O56 94.4(4) O69-Mn24-O56 165.4(4) O59-Mn24-O76 174.6(4) O69-Mn24-O76 86.0(4) O56-Mn24-O76 85.8(4) O59-Mn24-O75 105.9(4) O69-Mn24-O75 96.9(3) O56-Mn24-O75 93.5(4) O76-Mn24-O75 79.4(4) O76-Mn25-O77 120.2(3) O76-Mn25-O69 74.9(3) O77-Mn25-O69 154.4(4) O76-Mn25-N13 78.1(4) O77-Mn25-N13 75.5(4) O69-Mn25-N13 129.8(4) O76-Mn25-O70 114.3(3) O77-Mn25-O70 109.2(3) O69-Mn25-O70 78.5(3) N13-Mn25-O70 75.3(4) O76-Mn25-O80 78.6(3) O77-Mn25-O80 76.3(3) O69-Mn25-O80 88.0(3) N13-Mn25-O80 126.7(4)

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216 O70-Mn25-O80 157.6(4) O76-Mn25-O73 146.9(4) O77-Mn25-O73 73.7(3) O69-Mn25-O73 83.1(3) N13-Mn25-O73 134.7(3) O70-Mn25-O73 84.5(3) O80-Mn25-O73 76.1(3) O69-Mn26-O73 172.4(4) O69-Mn26-O74 99.2(4) O73-Mn26-O74 86.8(3) O69-Mn26-O68 100.1(3) O73-Mn26-O68 83.4(3) O74-Mn26-O68 99.4(3) O69-Mn26-O71 85.6(3) O73-Mn26-O71 87.1(3) O74-Mn26-O71 158.1(3) O68-Mn26-O71 100.8(3) O68-Mn27-O77 170.4(4) O68-Mn27-O66 96.8(4) O77 -Mn27-O66 88.8(4) O68-Mn27-O73 86.7(4) O77 -Mn27-O73 88.2(4) O66-Mn27-O73 175.4(4) O68-Mn27-O72 92.1(3) O77 -Mn27-O72 95.0(4) O66-Mn27-O72 96.9(4) O73-Mn27-O72 79.9(3) O68-Mn27-O67 93.4(3) O77 -Mn27-O67 77.8(3) O66-Mn27-O67 102.0(3) O73-Mn27-O67 80.7(3) O72-Mn27-O67 159.5(3) O74-Mn28-O71 82.8(3) O74-Mn28-O72 96.7(4) O71 -Mn28-O72 167.7(4) O74-Mn28-O70 166.3(4) O71 -Mn28-O70 84.7(4) O72-Mn28-O70 94.4(4) O74-Mn28-O82 94.0(4) O71 -Mn28-O82 99.1(4) O72-Mn28-O82 93.2(4) O70 -Mn28-O82 93.3(4) O74-Mn28-O73 78.7(3) O71 -Mn28-O73 87.9(3) O72-Mn28-O73 80.0(3) O70 -Mn28-O73 95.6(3) O82-Mn28-O73 169.2(3) O80-Mn29-O67 84.3(4) O80-Mn29-O71 165.5(4) O67 -Mn29-O71 97.1(4) O80-Mn29-O74 95.0(4) O67 -Mn29-O74 172.4(3) O71 -Mn29-O74 81.6(3) O80-Mn29-O81 104.5(4) O67 -Mn29-O81 91.8(4) O71 -Mn29-O81 89.9(4) O74-Mn29-O81 95.8(4) O80-Mn29-O73 86.9(4) O67 -Mn29-O73 85.0(3) O71 -Mn29-O73 78.9(3) O74-Mn29-O73 87.4(3) O81-Mn29-O73 167.8(3) O67 -Mn30-O80 83.4(4) O67 -Mn30-O62 102.2(4) O80-Mn30-O62 169.7(5) O67 -Mn30-O78 163.1(4) O80-Mn30-O78 79.8(4) O62 -Mn30-O78 94.2(4) O67 -Mn30-O83 94.8(4) O80-Mn30-O83 97.0(4) O62 -Mn30-O83 91.2(4) O78-Mn30-O83 89.0(4) O67 -Mn30-O77 81.0(3) O80-Mn30-O77 81.6(4) O62 -Mn30-O77 90.7(4) O78-Mn30-O77 94.9(4) O83-Mn30-O77 175.6(4) O75-Mn31-O80 91.6(4) O75-Mn31-N16 98.7(5) O80-Mn31-N16 167.0(5) O75-Mn31-O78 166.7(4) O80-Mn31-O78 77.7(4) N16-Mn31-O78 91.0(5) O75-Mn31-O79 96.5(4) O80-Mn31-O79 93.0(4) N16-Mn31-O79 93.8(4) O78-Mn31-O79 92.0(4) O75-Mn31-O76 78.0(4) O80-Mn31-O76 83.8(3) N16-Mn31-O76 90.4(4) O78-Mn31-O76 92.8(4) O79-Mn31-O76 173.6(4)

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217 Table A-14. Selected interatomic distances () and angles () for [Mn4O3Cl4(O2CEt)3(py)3]4MeCN (14MeCN) Mn1 O3 1.926(3) Mn1 N1 2.055(4) Mn1 O1 2.153(3) Mn1 Cl1 2.2334(16) Mn1 Cl2 2.6347(14) Mn2 O3 1.871(3) Mn2 O2 1.949(3) O3 Mn1 N1 171.26(17) O3 Mn1 O1 91.59(13) O3 Mn1 N1 91.04(15) O3 Mn1 O1 85.70(13) N1 Mn1 O1 91.68(15) O3 Mn1 O3 81.13(19) O3 Mn1 Cl1 93.50(11) O3 Mn1 Cl1 174.63(11) N1 Mn1 Cl1 94.29(13) O1 Mn1 Cl1 94.77(11) O3 Mn1 Cl2 84.86(10) O3 Mn1 Cl2 84.11(9) N1 Mn1 Cl2 90.51(12) O1 Mn1 Cl2 169.62(11) Cl1 Mn1 Cl2 95.18(5) O3 Mn2 O3 85.07(14) O3 Mn2 O2 177.77(15) Mn2 O3 Mn 1 95.70(15) Mn2 O3 Mn1 94.39(15) Mn1 O3 Mn 1 114.31(15)

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218 Table A-15. Selected interatomic di stances () and angles () for [Mn4O3Cl4(O2CEt)3(d5py)3]4MeCN (15MeCN) Mn1 O4 1.860(2) Mn2 O4 1.920(3) Mn1 O3 1.942(3) Mn2 N1 2.044(3) Mn2 O2 2.146(3) Mn2 Cl2 2.6310(12) Mn2 Cl1 2.2300(12) O4 Mn2 1.920(3) O4 Mn1 O4 84.87(11) O3 Mn1 O3 87.25(11) O4 Mn1 O3 95.25(11) O4 Mn2 O4 80.60(15) O4 Mn1 O3 92.64(11) O4 Mn2 N1 171.09(13) O4 Mn2 O2 91.63(10) N1 Mn2 O2 91.73(12) O4 Mn2 O2 85.58(10) O4 Mn2 Cl1 93.67(8) O4 Mn2 Cl1 174.27(8) N1 Mn2 Cl1 94.25(10) O2 Mn2 Cl1 94.91(9) O4 Mn2 Cl2 84.81(8) O2 Mn2 Cl2 169.44(8) Cl1 Mn2 Cl2 95.23(4) Mn1 O4 Mn2 96.05(12) Mn2 O4 Mn2 114.47(12) O4 Mn2 Cl2 84.03(7) N1 Mn2 Cl2 90.43(9) O4 Mn1 O3 177.49(12) O4 Mn2 N1 91.43(12)

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219 Table A-16. Selected interatomic distances () and angles () for [Mn4O3Cl4(O2CEt)3(py)3]C6H14 (16C6H14) Mn1-O2 1.9267(16) Mn1-O2 1.9516(16) Mn1-N1 2.057(2) Mn1-O1 2.1430(17) Mn1-Cl1 2.2328(7) Mn1-Cl2 2.6298(7) Mn2-O2 1.8704(16) Mn2-O2 1.8704(16) Mn2-O2 1.8704(16) Mn2-O3 1.9392(18) O2 -Mn1-O2 81.24(9) O2 -Mn1-N1 171.15(8) O2-Mn1-N1 90.44(8) O2 -Mn1-O1 90.76(7) O2'-Ni-O1' 92.94(5) O1'-Ni-N1' 82.31(5) O2-Mn1-O1 86.41(7) N1-Mn1-O1 91.74(8) O2 -Mn1-Cl1 93.56(5) O2-Mn1-Cl1 174.58(5) N1-Mn1-Cl1 94.67(6) O1-Mn1-Cl1 95.23(6) O2 -Mn1-Cl2 84.75(5) O2-Mn1-Cl2 84.28(5) N1-Mn1-Cl2 91.45(6) O1-Mn1-Cl2 170.18(5) Cl1-Mn1-Cl2 93.77(2) O2-Mn2-O2 84.91(7) O3-Mn2-O3 87.24(8) O2-Mn2-O3 93.52(7) O2-Mn2-O3 178.30(8) O2-Mn2-O3 94.31(7) Mn1-Cl2-Mn1 76.58(2) Mn2-O2-Mn1 95.46(7) Mn2-O2-Mn1 94.63(7) Mn1 -O2-Mn1 114.35(8)

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220 APPENDIX B LIST OF COMPOUNDS [Mn12(O2CMe)14(mda)8] (1) [Mn4(O2CPh)4(mda)2(mdaH)2] (2) [Mn6O2(OH)2(dpa)8(mdaH)2] (3) [Ni24(O2CMe)42(mdaH)6(EtOH)6] (4) [Ni(mdaH2)2](O2CMe)2 (5) [Fe22O14(OH)3(O2CMe)21(mda)6](ClO4)2 (6) [Fe7NaO3(O2CPh)9(mda)3]ClO4 (7) [Fe7O3(O2CPh)9(mda)3(H2O)] (8) [Fe7O3(O2CtBu)9(mda)3(H2O)3] (9) (HNEt3)[Mn7(mda)6Cl6] (10) (HNEt3)[Mn7(mda)6Cl6] (11) {Na(HOMe)3[Mn7(mda)6(N3)6]}n (12) [Mn18O11(OH)(N3)12(tea)3(teaH)3(OMe)(HOMe)] (13) [Mn31O20(N3)4(O2CMe)23(tea)2(dea)2(OMe)6(MeOH)2]n (14) [Mn4O3Cl4(O2CEt)3(py)3]4MeCN (15) [Mn4O3Cl4(O2CEt)3(d5-py)3]4MeCN (16) [Mn4O3Cl4(O2CEt)3(py)3]C6H14 (17) [Mn4O3Cl4(O2CEt)3(py)3]C6H12 (18) [Mn4O3Cl4(O2CEt)3(py)3]C8H16 (19) [Mn4O3Cl4(O2CEt)3(py)3]o-Cl2C6H4 (20)

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221 APPENDIX C PHYSICAL MEASUREMENTS IR spectra were recorded as KBr discs on a Nicolet model 510P spectrophotometer. Raman spectra were obtained using a JY Horiba LabRam HR800 microRaman spectrograph at room temperature. An 80 mW laser emitting at 785 nm was used as the excitation source. Care was taken to minimize laser damage to the sample as previously discussed. A 50 X 0.10 NA (numerical apertu re) objective with exposure times of 60 s averaged through ten scans was found to be su fficient for obtaining a reasonably strong spectrum. Elemental analyses were performed at the in -house facilities of the University of Florida Chemistry Department. Magnetic susceptibility data (direct current (dc) and alternating current (ac)) were recorded on a Quantum Design MPMS-XL SQ UID magnetometer equipped with a 7 T magnet and capable of operating in the 1. 8 400 K temperature range. Dc magnetic susceptibility data were collected on crushed cr ystalline samples that were restrained in eicosane to prevent torquing. Ac magnetic susceptibility measurements were performed in an oscillating ac field of 3.5 G and a zero dc field. The ac oscillation frequencies were in the 25 1488 Hz range. Pascal’s constant s were used to estimate the diamagnetic correction, which was subtracted from the expe rimental susceptibility to give the molar paramagnetic susceptibility ( M). Magnetic studies below 1.8 K were carried out on single crys tals using a microSQUID apparatus operating down to 0.04 K.

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222 Inelastic Neutron Scattering (INS) experiments were performed on IRIS at the ISIS Facility, CCLRC Rutherford Appleton Laborator y in Chilton, UK, and on IN5 at the Institut Laue-Langevin (ILL) in Grenoble, France. Spectra were acquired in the temperature range 1.5 K 20 K on 4.4 grams of an undeuterated ([Mn4O3Cl4(O2CEt)3(py)3]28MeCN) and a partially deuterated ([Mn4O3Cl4(O2CEt)3(pyd5)3]2MeCN), microcrystal line sample of (Mn4)2 sealed in a annular shaped aluminium cylinder with dimensions din = 20 mm, dout = 24 mm, h = 50 mm (IRIS) and din = 9 mm, dout = 15 mm, h = 50 mm (IN5). On IRIS, spectra of both, the partially deuterated and undeuterated compound were recorded using a pyrolytic graphite (P G002) analyzer with a final wavelength f = 6.6 (FWHM = 17.5 eV at zero energy transfer) in the energy transfer range from -0.3 meV to 1.2 meV. The accessible Q range was 0.4 -1 to 1.6 -1. The time-of-flight to energy conversion and re duction of IRIS data were done with the ISIS Facility analysis packages IDA and MSLICE.15 The IN5 data were measured on an undeuterated sample with an incident wavelength i = 7.0 corresponding to a FWHM = 31 eV at zero energy transfer. The energy transfer range was -0.9 meV to 1.1 meV with an accessible Q range from 0.2 -1 to 1.6 -1. The time-of-flight to energy conversion and the data reduction employed the standa rd program INX (ILL). The data were corrected for detector efficiency by means of a spectrum of vanadium metal. In both experiments the data correspond to the sum of all available detectors. Further data treatment included subtraction of the bac kground by approximating it with a suitable analytical function. Computational Methods were performed at Indiana University-Purdue University Indianapolis. The ZILSH method estimates the exchange constants of a complex by

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223 assuming that wavefunctions for various spin components fit a Heisenberg Hamiltonian with energies given by B A i B A AB 0 iS S J 2 E E (C-1) where E0 includes all spin-independen t terms. The energies Ei of the spin components are obtained from semiempirical molecular or bital calculations w ith the INDO/S method, and spin couplings B AS S are calculated for each component from the INDO/S density with Davidson’s local spin formalism. Given these quantities, the exchange parameters JAB are obtained by simultaneous solution of equations (C-1) for a number of spin components equal to the number of paramete rs. While both energies and spin couplings calculated for component wavefunctions suffe r from spin contamination, it has been shown that the exchange constants ar e approximately free of this error.i The spin states of a complex can be studied by substituting exchange constants found as just described into the Heisenberg spin Hamiltonian (HSH). Assuming that the metals retain their formal spin values (e.g., SA = 2 5 for Fe3+), diagonalization in a basis of spin components N N 2 2 1 1M S M S M S (more succinctly, N 2 1M M M) yields state energies and wavefunctions. This can be done for all spin states for small complexes of up to six metal ions. For larger complexes such as those considered here, standard sparse matrix techniques can be us ed to obtain the energi es and wavefunctions of the lowest-energy state of each spin . The wavefunctions are of the form i i N 2 1 M iM M M C SM (C-2) where labels states with spin S and z-co mponent M, i labels components with N 2 1M M M M , and M iC are expansion coefficients.

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224 Several quantities provide information about spin alignments in the ground state. For ground states of nonzero spin, the component with the largest e xpansion coefficient indicates the directions of spin for each meta l, although the actual spin moment of each is generally attenuated by the admixture of ot her components. For a more quantitative description, the z-components of spin of each metal in the ground state can be calculated directly via the local spin forma lism. Finally, the spin couplings B AS S computed for the ground state wavefunction are diagnostic for sp in frustration. The exchange constant reflects the preferred spin alignmen t over an exchange pathway, while B AS S reflects the actual alignment, so the pathway is fr ustrated if these two quantities have opposite sign. Furthermore, in a more quantitative se nse, the contribution of each pathway to the total energy of the ground state is given by the HSH as B A ABS S J 2 . Frustrated pathways are then easily identified as thos e that increase the ener gy of the ground state. All of these approaches were used to analyze spin alignments in complexes 7, 8, and 9. The ZILSH method has been applied previ ously to fourteen exchange-coupled Fe3+ complexes, yielding reasonable estimates of the exchange constants and correctly predicting the spin of the ground state in each case. All ZILSH calculations followed the procedure described in reference 45. After the calculations, assuming a S = 2 5 ground state, the spin alignments in the complexes 7, 8 and 9 are clearly established by both the wavefunctions and properties computed from them. The leading compone nt of the wavefunction in each case is 2 5 2 5 2 5 2 5 2 5 2 5 2 5 . This component makes up about 25% of the wavefunction for each complex, with the remainder composed of components with the same pattern of spin

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225 directions, but reduced z-components of spin fo r the various metal ions. For example, the second leading component of the ground state of complex 7 is 2 5 2 3 2 5 2 5 2 3 2 5 2 5 , representing about 3% of the wavefunction. The admixture of these other components lowers the absolute values of the zcomponents of spin of each metal below 2 5, but the spin alignments are still clea rly reflected by the resulting values (see Chapter 4, point 4.3.4., Table 4-6): three of the spins in the outer ring are aligne d parallel to the spin of the central metal ion, while the othe r three are aligned antiparallel to it, leading to a total spin of + 2 5.

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226 APPENDIX D VAN VLECK EQUATIONS D-1. Van Vleck equation for [Mn4(O2CPh)4(mda)2(mdaH)2] (2) Mn4 Mn2 Mn1 Mn3 JbbJwbJww Mn4 Mn2 Mn1 Mn3 JbbJwbJww M = [(1-p)(C g2)/ T) + [630 exp (0 l+ 0 m+ 0 n) + 6 exp (2 l+ 0 m+ 0 n) + 0 exp (2 l+ 4.0 m+ 2 n) + 630 exp (2 l+ -2 m+ 2 n) + 30 exp (2 l+ 2 m+ 2 n) + 6 exp (2 l+ -6 m+ 6 n) + 84 exp (2 l+ 4 m+ 6 n) + 30 exp (2 l+ -8 m+ 12 n) + 180 exp (2 l+ 6 m+ 12 n) + 84 exp (2 l+ -10 m+ 20 n) + 330 exp (2 l+ 8 m+ 20 n) + 180 exp (2 l+ -12 m+ 30 n) + 546 exp (2 l+ 10 m+ 30 n) + 114 exp (6 l+ 0 m+ 0 n) + 630 exp (6 l+ -6 m+ 2 n) + 30 exp (6 l+ -2 m+ 2 n) + 414 exp (6 l+ 4 m+ 2 n) + 30 exp (6 l+ -12 m+ 6 n) + 6 exp (6 l+ -10 m+ 6 n) + 180 exp (6 l+ 8 m+ 6 n) + 186 exp (6 l+ -16 m+ 12 n) + 180 exp (6 l+ 2 m+ 12 n) + 330 exp (6 l+ 12 m+ 12 n) + 30 exp (6 l+ -20 m+ 20 n) + 84 exp (6 l+ -14 m+ 20 n) + 546 exp (6 l+ 16 m+ 20 n) + 84 exp (6 l+ -24 m+ 30 n) + 546 exp (6 l+ 6 m+ 30 n) + 840 exp (6 l+ 20 m+ 30 n) + 630 exp (12 l+ 0 m+ 0 n) + 30 exp (12 l+ -8 m+ 2 n) + 414 exp (12 l+ 2 m+ 2 n) + 510 exp (12 l+ 6 m+ 2 n) + 6 e xp (12 l+ -16 m+ 6 n) + 624 exp (12 l+ -12 m+ 6 n) + 84 exp (12 l+ -6 m+ 6 n) + 180 e xp (12 l+ 2 m+ 6 n) + 330 exp (12 l+ 12 m+ 6 n) + 0 exp (12 l+ -24 m+ 12 n) + 186 exp ( 12 l+ -22 m+ 12 n) + 30 exp (12 l+ -18 m+ 12 n) + 180 exp (12 l+ -4 m+ 12 n) + 546 exp ( 12 l+ 18 m+ 12 n) + 90 exp (12 l+ -30 m+ 20 n) + 30 exp (12 l+ -26 m+ 20 n) + 84 exp ( 12 l+ -20 m+ 20 n) + 546 exp (12 l+ 10 m+ 20 n) + 840 exp (12 l+ 24 m+ 20 n) + 30 exp ( 12 l+ -36 m+ 30 n) + 840 exp (12 l+ 14 m+ 30 n) + 1224 exp (12 l+ 30 m+ 30 n) + 180 exp (20 l+ 0 m+ 0 n) + 414 exp (20 l+ -10 m+ 2 n) + 510 exp (20 l+ -2 m+ 2 n) + 330 exp (20 l+ 8 m+ 2 n) + 624 exp (20 l+ -20 m+ 6 n) + 84 exp (20 l+ -14 m+ 6 n) + 180 exp (20 l+ -6 m+ 6 n) + 330 exp (20 l+ 4 m+ 6 n) + 1386 exp (20 l+ 16 m+ 6 n) + 186 exp (20 l+ -3 0 m+ 12 n) + 30 exp (20 l+ -26 m+ 12 n) + 180 exp (20 l+ -12 m+ 12 n) + 546 exp (20 l+ 10 m+ 12 n) + 840 exp (20 l+ 24 m+ 12 n) + 0 exp (20 l+ -40 m+ 20 n) + 90 exp ( 20 l+ -38 m+ 20 n) + 30 exp (20 l+ -34 m+ 20 n) + 84 exp (20 l+ -28 m+ 20 n) + 546 exp (20 l+ 2 m+ 20 n) + 1224 exp (20 l+ 32 m+ 20 n) + 6 exp (20 l+ -48 m+ 30 n) + 30 exp (20 l+ -44 m+ 30 n) + 546 exp (20 l+ -8 m+ 30 n) + 840 exp (20 l+ 6 m+ 30 n) + 1224 exp (20 l+ 22 m+ 30 n) + 1710 exp (20 l+ 400 m+ 300 n)/ + 36 exp (0 l+ 0 m+ 0 n) + 3 exp (2 l+ 0 m+ 0 n) + 1 exp (2 l+ -4 m+ 2 n) + 35 exp (2 l+ -2 m+ 2 n) + 5 exp (2 l+ 2 m+ 2 n) + 3 exp (2 l+ -6 m+ 6 n) + 7 exp (2 l+ 4 m+ 6 n) + 5 exp (2 l+ -8 m+ 120 n) + 9 exp (2 l+ 6 m+ 12 n) + 7 exp (2 l+ -10 m+ 20 n) + 11

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227 exp (2 l+ 8 m+ 20 n) + 9 exp (2 l+ -12 m+ 30 n) + 13 exp (2 l+ 10 m+ 30 n) + 12 exp (6 l+ 0 m+ 0 n) + 35 exp (6 l+ -6 m+ 2 n) + 5 exp (6 l+ -2 m+ 2 n) + 18 exp (6 l+ 4 m+ 2 n) + 6 exp (6 l+ -120 m+ 6 n) + 3 exp (6 l+ -10 m+ 6 n) + 9 exp (6 l+ 8 m+ 6 n) + 12 exp (6 l+ -16 m+ 12 n) + 9 exp (6 l+ 2 m+ 12 n) + 11 exp (6 l+ 12 m+ 12 n) + 5 exp (6 l+ -20 m+ 20 n) + 7 exp (6 l+ -14 m+ 20 n) + 13 exp (6 l+ 16 m+ 20 n) + 7 exp (6 l+ -24 m+ 30 n) + 13 exp (6 l+ 6 m+ 30 n) + 1 exp (6 l+ 20 m+ 30 n) + 20 exp (12 l+ 0 m+ 0 n) + 5 exp (12 l+ -8 m+ 2 n) + 18 exp (12 l+ -2 m+ 2 n) + 20 exp (12 l+ 6 m+ 2 n) + 3 exp (12 l+ -16 m+ 6 n) + 32 exp (12 l+ -12 m+ 6 n) + 7 exp (12 l+ -6 m+ 6 n) + 9 exp (12 l+ 2 m+ 6 n) + 11 exp (12 l+ 12 m+ 6 n) + 1 exp (12 l+ -24 m+ 12 n) + 12 exp (12 l+ -22 m+ 12 n) + 5 exp (12 l+ -18 m+ 12 n) + 9 exp (12 l+ -4 m+ 12 n) + 13 exp (12 l+ 18 m+ 12 n) + 10 exp (12 l+ -30 m+ 20 n) + 5 exp (12 l+ -26 m+ 20 n) + 7 exp (12 l+ -20 m+ 20 n) + 13 exp (12 l+ 10 m+ 20 n) + 15 exp (12 l+ 24 m+ 20 n) + 5 exp (12 l+ -36 m+ 30 n) + 15 exp (12 l+ 14 m+ 30 n) + 17 exp (12 0 l+ 30 m+ 30 n) + 9 exp (20 l+ 0 m+ 0 n) + 18 exp (20 l+ 10 m+ 2 n) + 20 exp (20 l+ -2 m+ 2 n) + 11 e xp (20 l+ 8 m+ 2 n) + 32 exp (20 l+ -20 m+ 6 n) + 7 exp (20 l+ -14 m+ 6 n) + 9 exp (20 l+ -6 m+ 6 n) + 11 exp (20 l+ 4 m+ 6 n) + 28 exp (20 l+ 16 m+ 6 n) + 12 exp (20 l+ -30 m+ 12 n) + 5 exp (20 l+ -26 m+ 12 n) + 9 exp (20 l+ -12 m+ 12 n) + 13 exp (20 l+ 10 m+ 12 n) + 15 exp (20 l+ 24 m+ 12 n) + 1 exp (20 l+ -40 m+ 20 n) + 10 exp (20 l+ -38 m+ 20 n) + 5 exp (20 l+ -34 m+ 20 n) + 70 exp (20 l+ -28 m+ 20 n) + 13 exp (20 l+ 2 m+ 20 n) + 17 exp (20 l+ 32 m+ 20 n) + 3 exp (20 l+ 48 m+ 30 n) + 5 exp (20 l+ -44 m+ 30 n) + 13 exp (20 l+ -8 m+ 30 n) + 15 exp (20 l+ 6 m+ 30 n) + 17 exp (20 l+ 22 m+ 30 n) + 19 exp (20 l+ 40 m+ 30 n)]+TIP+(35/4) Cg2p] p = paramagnetic impurity C = N B/3k N = Avogadro's number g = Lande's factor B = Bohr magneton k = Boltzmann constant T = Temperature TIP = Temperature inde pendent paramagnetism l=Jbb/k/T m=Jwb/k/T n=Jww/k/T

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228 D-2. Van Vleck equation for complexes [Mn4O3Cl4(O2CEt)3(py/d5-py)3] J33 J34 J33 J34 M = [(1-p)(C g2)/ T) + [7.5 exp (-5.25 m+ 6 n) + 75 exp (-2.25 m+ 6 n) + 262.5 exp (2.75 m+ 6 n) + 630 exp (9.75 m+ 6 n) + 4.5 exp (-1.25 m+ 2 n) + 45 exp (1.75 m+ 2 n) + 57.5 exp (6.75 m+ 2 n) + 60 exp (-8.25 m+ 12 n) + 210 exp (-3.25 m+ 12 n) + 504 exp (3.75 m+ 12 n) + 990 exp (12.75 m+ 12 n) + 15 exp (3.75 m+ 0 n) + 157.5 exp (-11.25 m+ 20 n) + 378 exp (-4.25 m+ 20 n) + 742.5 exp (4.75 m+ 20 n) + 1287 exp (15.75 m+ 20 n) + 252 exp (-14.25 m+ 30 n) + 495 exp (-5 .25 m+ 30 n) + 858 exp (5.75 m+ 30 n) + 1365 exp (18.75 m+ 30 n) + 247.5 exp (-17.25 m+ 42 n) + 429 exp (-6.25 m+ 42 n) + 682.5 exp (6.75 m+ 42 n) + 1020 exp (21.75 m+ 42 n) / + 10 exp (-5.25 m+ 6 n) + 20 exp (-2.25 m+ 6 n) + 30 exp (2.75 m+ 6 n) + 40 e xp (9.75 m+ 6 n) + 6 exp (-1.25 m+ 2 n) + 12 exp (1.75 m+ 2 n) + 18 exp (6.75 m+ 2 n) + 16 exp (-8.25 m+ 12 n) + 24 exp (-3.25 m+ 12 n) + 32 exp (3.75 m+ 12 n) + 40 exp ( 12.75 m+ 12 n) + 4 exp (3.75 m+ 0 n) + 18 exp (-11.25 m+ 20 n) + 24 exp (-4.25 m+ 20 n) + 30 exp (4.75 m+ 20 n) + 36 exp (15.75 m+ 20 n) + 16 exp (-14.25 m+ 30 n) + 20 exp (5.25 m+ 30 n) + 24 exp (5.75 m+ 30 n) + 28 exp (18.75 m+ 30 n) + 10 exp (-17.25 m+ 42 n) + 12 exp (-6.25 m+ 42 n) + 14 exp (6.75 m+ 42 n) + 16 exp (21.75 m+ 42 n)]+TIP] p = paramagnetic impurity C = N B/3k N = Avogadro's Number g = Lande's factor B = Bohr magneton k = Boltzmann constant T = Temperature TIP = Temperature inde pendent paramagnetism m=J34/k/T n=J33/k/T

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241 BIOGRAPHICAL SKETCH Dolos Foguet-Albiol was born in Vinars, Spain on February 25, 1973. She received a Bachelor of Science degree from the University of Barcelona in February 2000. During her undergraduate studies, sh e was a journalist for the magazine Food Science and Technology , and also performed several intern ships in the industry. After her undergraduate studies, she was awarded the pr estigious “Leonardo Da Vinci” fellowship to work in a company, in The Netherlands , investigating the development of a low chemical oxygen demand wet-temper rolli ng agent, and studing the effect and reproducibility of different test methods by design of experiments. Thereafter, she worked in a multinational pharmaceutical co mpany in Spain. Finally, she joined the research group of Professor George Chri stou in the Chemistry Department at the University of Florida in January 2002, to pursue her doctoral studies. Her doctoral research focuses on the synthesis and physic al and magnetic char acterization of high nuclearity polynuclear transition metal comp lexes, some of which behave as singlemolecule magnets.