Group Title: investigation of some magnetically anomalous cobalt (II) complexes
Title: An Investigation of some magnetically anomalous cobalt (II) complexes
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Title: An Investigation of some magnetically anomalous cobalt (II) complexes
Physical Description: ix, 128 l. : illus. ; 28 cm.
Language: English
Creator: Fisher, Harold Manly, 1940-
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 1966
Copyright Date: 1966
 Subjects
Subject: Cobalt   ( lcsh )
Magnetic measurements   ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
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Thesis: Thesis - University of Florida.
Bibliography: Bibliography: l. 124-127.
Additional Physical Form: Also available on World Wide Web
General Note: Manuscript copy.
General Note: Vita.
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Bibliographic ID: UF00097854
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000424018
oclc - 11069291
notis - ACH2423

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AN INVESTIGATION OF SOME

MAGNETICALLY ANOMALOUS COBALT(II)

COMPLEXES










By
HAROLD MANLY FISHER


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY











UNIVERSITY OF FLORIDA
August, 1966












ACKNOWLEDGMENTS


The author wishes to express his sincere appreciation

to Dr. R. C. Stoufer, chairman of the author's Supervisory

Committee, and to the other members of his Supervisory

Committee. For the patience, guidance, and advice given

by Dr. R. C. Stoufer, the author expresses his sincere

gratitude.

Special thanks are due those involved in the

measurement of the electron paramagnetic resonance spectra,

particularly Dr. W. S. Brey, Jr., Dr. M. R. Chakrabarty,

Mr. N. S. Morales, and Mr. D. L. Williams. The typing of

this manuscript by Mrs. Edwin N. Johnston is deeply

appreciated.

The author is especially grateful to his wife,

Mary Lee, without whose constant encouragement and faith

this dissertation might never have been completed.

Support of this research by the National Science

Foundation is gratefully acknowledged.













TABLE OF CONTENTS

Page

ACKNOLEDGENTS . . . . . . . . . ii

LIST OF TABLES. . . . .. . . . . iv

LIST OF FIGURES. . . . . . . . vi

INTRODUCTION. . . . . . . . .

EXERIENTAL PROCEDURES . . . . . . . 11

Apparatus. . . . . . . . . . 19

RESULTS . . . . . ..... . . 23

Magnetic Measurements. . . . . . . . 2

X-Ray Diffraction Measurements . . . . 61

Conductance Measurements . . . . . 77

Spectral Measurements . . . . . . 78

DISCUSS :. . . . . . ... . . .

SUlMAl RY . . . . . . . . . . . 97

APPE-DICES. . . . . . . . . . . 99

BIBLIOGRAPHY. . . . . . . . .... 124

BIOGRAPHICAL SKETCH . . . . . . . .. 128










iii












LIST OF TABLES


Table Page
1. Room-Temperature Magnetic Moments and
Temperature of 1/% Maxima of Cobalt(II)
Complexes Exhibiting Anomalous Curie-Weiss
Behavior . . . . . . . . . 6
2. Magnetic Moments of Solids and Solutions at
Room Temperature . . . . . . .. 2

3. Variation of Molar Susceptibilities and
Magnetic Moments of [Co(PvdH)3]I2 and
[Co(PvdH) ](C104)2 with Temperature. . . 29
4. Variation of Molar Susceptibilities and
Magnetic Moments of [Co(PvdH)3](N03)2 and
[Co(PvdH)3][B(C6H5)4]2 with Temperature. . 32
5. Variation of Molar Susceptibilities and
Magnetic Moments of [Co(BdH)3]Br2 and
[Co(BdH)3]I2 with Temperature. . . . .. 35
6. Variation of Molar Susceptibilities and
Magnetic Moments of [Co(BdH)3](C104)2 and
[Co(BdH)3](N03)2 with Temperature. . ... 38
7. Variation of Molar Susceptibilities and
Magnetic Moments of [Co(BdH) ][B(C6H5)4]2 and
[Co(terpy)2](N03)2 with Temperature. . . 41
8. Variation of Molar Susceptibilities and
Magnetic Moments of [Co(terpy)2]C12-5H20 and
[Co(terpy)2]C12.4H20 with Temperature. ... 44
9. Variation of Molar Susceptibilities and
Magnetic Moments of [Co(terpy)2]Br2-H20 and
[Co(terpy)212.*H20 with Temperature. . . 47









Table

10. Variation of Molar Susceptibilities and
;cn.-etic Moments of [Co(terpy)2](C104)2)HO
and Anoxic [Co(terpy)2](C014)2*H20 with
Temperature . . . . . . .

11. Variation of Molar Susceptibilities and
-: "netic Moments of [Co(terpy)2](C104)2 and
[Co(terpy)2][B(C6H5)4]2 with Temperature.

12. Variation of Molar Susceptibilities and
-r"netic Moments of [Co(terpy)2]SO4*2H20
with Temperature. . . . . . . .

13. Diffuse Reflectance Spectra and Electron
Paramagnetic Resonance g Values . . .

14. -Aproximate Sizes of Ions . . . . .

15. Susceptibility Corrections for Diamagnetism

16. Complete X-Ray Diffraction Patterns of
Complexes . . . . . . . . .


Page


. .


S 79

S. .95

S. 00


. 101













LIST OF FIGURES


Figure

1. Temperature dependent susceptibility of
[Co(PvdH) ]I . . . . . .

2. Temperature dependent susceptibility of
[Co(PvdH) ](C104)2. . . . ....

3. Temperature dependent susceptibility of
[Co(PvdH) ](NO3)2 . . . . .

4. Temperature dependent susceptibility of
[Co(PvdH) ][B(C6H5)4]2 . ....

5. Temperature dependent susceptibility of
[Co(BdH) ]Br2 . . . . . .

6. Temperature dependent susceptibility of
[Co(BdH)3]I12 . . . . . .

7. Temperature dependent susceptibility of
[Co(BdH)](ClO4)2 . . . . .

8. Temperature dependent susceptibility of
[Co(BdH)3](NO3)2 . . . ..

9. Temperature dependent susceptibility of
[Co(BdH) ][B(C6H5)4)2 . . . .

10. Temperature dependent susceptibility of
[Co(terpy)2](N03)2 . . . .

11. Temperature dependent susceptibility of
[Co(terpy)2]C12.5H20.. . . ..

12. Temperature dependent susceptibility of
[Co(terpy)2]C124H20. .. . ...

15. Temperature dependent susceptibility of
[Co(terpy)2]BrH2 . . . . .

14. Temperature dependent susceptibility of
[Co(terpy)2]12-H20. . . . .


Page


. . 27


S. 28


. 30


. .. 31


S. 33


34


36


37


39

40


42


. . 453


. . 45


. 46





















Figure Page

15. Temperature dependent susceptibility of
[Co(terpy)2](C104)2*H20 . . . . . 48

16. Temperature dependent susceptibility of
anoxic [Co(terpy)2](C104)2.H20. . . . 49

17. Temperature dependent susceptibility of
[Co(terpy)2](C104)2 . . . . . . 51
18. Temperature dependent susceptibility of
[Co(terpy)2][B(C6H5)4]2 .* .. . . .. 52
19. Temperature dependent susceptibility of
[Co(terpy)2]SO4"2H20. . . . . . . 54
20. Temperature dependent susceptibilities of
[Co(PvdH)3] complexes . . . .. .. 56
21. Temperature dependent susceptibilities of
[Co(BdH) ]2+ complexes. . . . . . 57
22. Temperature dependent susceptibilities of
some [Co(terpy)2]2+ complexes . . . . 58
23. Temperature dependent susceptibilities of
remaining [Co(terpy)2]2+ complexes. . . 59
24. Temperature dependent magnetic moments of
[Co(PvdH)3]2+ complexes . . . . . 62
25. Temperature dependent magnetic moments of
[Co(BdH)3]2+ complexes. . . . . . 63
26. Temperature dependent magnetic moments of
some [Co(terpy)2]2+ complexes . . ... 64
27. Temperature dependent magnetic moments of
remaining [Co(terpy)2]2+ complexes. . . 65
28. X-ray diffraction pattern of [Co(PvdH) ]Br2
at three temperatures . . . . . 66
29. X-ray diffraction pattern of [Co(PvdH) 3]2
at three temperatures . . .. . 66


vii










30. X-ray diffraction pattern of
[Co(PvdiH)3](C10)2 at three temperatures . 67

31. X-ray diffraction pattern of
[Co(PvdH)3](NO )2 at three temperatures. . 67

32. X-ray diffraction pattern of
[Co(PvdH) ][B(C6H5 ]2 at three temperatures 68

55. X-ray diffraction pattern of
[Co(BdH)3]Br2 at three temperatures. . . 68

54. X-ray diffraction pattern of
[Co(BdH) ]I2 at three temperatures . .. 69

35. X-ray diffraction pattern of
[Co(BdH)3](C104)2 at three temperatures. . 69

56. X-ray diffraction pattern of
[Co(BdH)3](NO3)2 at three temperatures . 70

37. X-ray diffraction pattern of
[Co(BdH)3][B(C6H )4]2 at three temperatures. 70

58. X-ray diffraction pattern of
[Co(terpy)2]C125H20 at three temperatures 71

59. X-ray diffraction pattern of
[Co(terpy)2]C124H20 at three temperatures 71
40. X-ray diffraction pattern of
[Co(terpy)2]Br2'H20 at three temperatures. 72
41. X-ray diffraction pattern of
[Co(terpy)2]32-H20 at three temperatures . 72
42. X-ray diffraction pattern of
[Co(terpy)2](C104)2-H20 at three
temperatures . ... . .. . . 75

43. X-ray diffraction pattern of
[Co(terpy)2](C104) at three temperatures . 75
44. X-ray diffraction pattern of
[Co(terpy)2][B(C6H5)4]2 at three
temperatures . . . . . 74


viii


Page


Figure









Figure


Page


45. X-ray diffraction pattern of
[Co(terpy)2]S04 2H20 at three temperatures . 74

46. X-ray diffraction pattern of
[Co(terpy)2](N03)2 at three temperatures . 75
7
47. Energy level diagram for the d7 configuration
in an octahedral field . . . . 82












INTRODUCTION


During the past sixty or seventy years, the field of

coordination chemistry has grown from a small and limited

area to what is presently the most active area of inorganic

chemical research. Many different approaches have been

used to investigate such properties as the stereochemistry

and bonding of coordination compounds. One such approach,

the measurement and interpretation of the magnetic proper-

ties of transition metal compounds, has been particularly

successful in contributing to the development and under-

standing of coordination chemistry.

For many years the magnetic moment has been used as

a reliable indication of structure, that is, whether a

complex is octahedral, tetrahedral, or square planar, the

spin and orbital angular moment contributions differing in

many instances with these three stereochemistries. Much of

the present interest in cobalt(II) is due to the fact that

its complexes are illustrative of a rather large spectrum

of stereochemical and magnetic properties common to transi-

tion metal complexes. The great majority of the complexes

of cobalt(II) are octahedral, exhibiting magnetic moments

between 4.7 and 5.2 Bohr magnetons (B.M.) (25,26). The








2

magnitude of magnetic moments in this range is attributable

to a spin contribution of three unpaired electrons and a

rather large orbital contribution. The large orbital

contribution arises from the fact that an octahedral field

about the cobalt(II) ion splits the F free ion term state

into three new levels, T1, T2, and A2, of which the

ground level is T4T (42). The threefold orbital degeneracy

in the ground level is responsible for a large contribution

to the magnetic moment of the complex (38,41). Additional

orbital contribution is attributed to mixing of spin states

of higher energy with the ground state (58). Octahedral

complexes as described above are said to be "high spin."

Not all octahedral cobalt(II) complexes are high

spin, however. When the ligand field strength is large,

the crystal field splitting of the d orbitals increases,

and eventually spin pairing occurs. The ground state cor-

responding to the new electronic configuration is 2E, and

the complex is said to be "low spin." A small number of

cobalt(II) complexes are known which fit into this category,

exhibiting magnetic moments in the vicinity of 1.8 to 2.2

3.K. (6,48).

In tetrahedral complexes the energy levels are in-

verted from the order of octahedral complexes and the ground

state for cobalt(II) is A2, an orbital singlet. Thus, the

orbital contribution to the magnetic moment is much less










than in the case of the octahedral complexes, arising

principally from the mixing in of spin states of higher

energy, and the resulting range of magnetic moments for

tetrahedral cobalt(II) complexes is 4.1 to 4.5 B.M. (50,

55,36,38). Low-spin tetrahedral cobalt(II) complexes are

not known.

Most square planar cobalt(II) complexes are of the

low-spin variety, exhibiting magnetic moments in the

vicinity of 2.1 to 2.9 B.M. (6,38,48). Only a few complexes

of cobalt(II) known to be square planar are high spin; these

exhibit magnetic moments between 4.8 and 5.2 B.M. (14,15,17).

Ranges such as those listed above, however, are not strict,

and exceptions are becoming more common as they are sought

and as more complexes are prepared.

Transition metal complexes exhibiting unusual inter-

mediate magnetic moments have uncovered several new areas

for research. In several instances unusual magnetic be-

havior has led to the discovery that the complex in question

was not a monomeric species, but a polymer, containing two,

three, or more metal ions per formula weight (31,32).

Nickel(II) complexes with various N-alkylsalicylaldimines

and other ligands have been found to exist in square planar-

tetrahedral equilibria, depending upon temperature, solvent,

and size and position of substituent groups (2,20,46,47).









Existence of a planar-tetrahedral equilibrium of some

cobalt(II) complexes in solution has been postulated (20,

40). Recently, however, increased interest has been

focused upon an area in which the equilibrium apparently

is not between structures but rather between electronic

states (9,11,21,22,34,53,54,55).

Normal magnetic behavior, which follows the Curie-

Weiss law, is described by the equation X= C/(T + 9).

This is represented graphically by plotting 1/X versus T,

in which case a straight line is obtained with a slope of

1/C and intercept of 0/C. Cambi and Szego reported a series

of closely related iron(III) complexes whose magnetic be-

havior is quite different from that usually followed by

transition metal complexes (11). The plots of the iron(III)

complexes in question are not straight lines. This anomalous

Curie-Weiss behavior led to the suggestion that the complexes

exist in a temperature-dependent equilibrium of high-spin

and low-spin forms, shifting toward the low-spin form at low

temperatures. The work by Cambi and Szego has been verified

and extended recently to a series of nineteen N,N-disubsti-

tuted dithiocarbamates of iron(III). The anomalous magnetic

moments were found to persist in chloroform and benzene

solutions as well as in the solid state (21,55).

In 1956 Stoufer and Busch reported anomalous Curie-

Weiss behavior for a cobalt(II) complex (55). A Boltzmann








5

distribution over high- and low-spin states was postulated.

Research in this area has continued and the 1/% versus T

curves of nine anomalous cobalt(II) complexes have now

been published (28,29,44,53,55). These are listed in Table

1 with their room-temperature magnetic moments.

In the various attempts to explain the anomalous

magnetic behavior of these cobalt(II) complexes, several

correlations have been attempted. It appears that a dis-

proportionate number of anomalous complexes have tridentate

ligands. A complex possessing two identical tridentate

ligands such as 2,6-pyridinaldihydrazone has a unique axis

of symmetry passing through the middle donor atoms of the

tridentate ligands, giving rise to the possibility of Jahn-

Teller-like distortion. Such an expansion along the z

axis gives to the complex a structure approaching that of

a square plane with the additional result that the magnetic

moment is lowered to the 2.1 to 2.9 B.M. range. Research

carried out along these lines by Ramirez showed some validity

in the correlation (44). An anomalous complex was prepared

by the use of a tetradentate ligand occupying the four

planar positions and perchlorate ions, very weak donors, in

the trans positions. Ramirez showed theoretically that

whether the distortion is expansion or contraction along

the z axis, the complex is more likely to be low spin than

if there is no distortion at all.









TABLE 1

ROOM-TEMPERATURE MDAGNETIC NMOKITS AND TEMPERATURE OF 1/%,
MAXINA OF COBALT(II) COL:L I:IG ANOMALOUS
CURIE-WIS) ..VIOR


Complex


[Co(PHI)3](BF4)2
[Co(PBI)2],2

[Co(BMI) ]I2

[Co(PdAdH)2]I2

[Co(terpy)2]Br2"H20

[Co(DTPH)](ClO4)2

[Co(PvdH) ]Br2

[Co(GdH)3]Br2

[Co(PAPI)(C104)2]


eff


4.31

3.72
2.91

2.85

2.61

2.36

4.22

3.18
2.44


Temperature Reference
K of 1/X
maxima

1250 55

1750 55
2050 55

3000 55

2200 34

2850 55

(no maximum) 27

2850 27

2600 44


Abbreviations: PHI, 2-pyridinalmethylimine; PBI, 2,6-

pyridindialbis(benzylimine); BMI, biacetylbis(methylimine);

?dAdH, 2,6-pyridindialdihydrazone; terpy, 2,2',2"-terpyridine;

DTPH, 1,12-bis(2-pyridyl)-l,2,11,12-tetrakisaza-5,8-dithia-

A2'10-dodecadiene; PvdH, pyruvaldihydrazone; GdH, glyoxaldi-

hydrazone; PAPI, bis(2-pyridinal)-o-phenylenediimine.


_ __ _~~ ~_










Further research in the area of anomalous cobalt(II)

complexes has shown that ligand field strength and pi-bond-

ing capabilities of the ligand are definite factors involved

in causing the complex to exhibit an intermediate magnetic

moment (27,28,29). It was shown that by decreasing steric

repulsion and thus increasing the capability of pi-bonding,

the ligand field strength for a particular type of co-

ordinating group could be increased sufficiently to cause

the cobalt(II) complex to exhibit anomalous Curie-Weiss

behavior.

One argument for the lower magnetic moments of the

anomalous compounds was based on the possibility of the

complex actually being a mixture of high-spin cobalt(II)

and diamagnetic cobalt(III) (55). The ease of oxidation of

cobalt(II) complexes is well known (3,8,12,49). However,

it has now been proved conclusively by Schmidt that the

lower magnetic moments of the anomalous complexes are due

to the presence of appreciable concentrations of the low-

spin cobalt(II) species (50,51). Cobalt(III), being dia-

magnetic, does not exhibit an electron paramagnetic resonance

(EPR) spectrum, and the EPR spectrum of high-spin cobalt(II)

is extremely broad, with a g value of approximately 4. On

the other hand, the narrowness of the EPR spectrum of low-

spin cobalt(II), with a g value of approximately 2.1, makes










low-spin cobalt(II) especially well suited for EPR in-

vestigation (50,51).

Williams has shown that spin-orbit coupling affords

an explanation of the existence of intermediate magnetic

moments of cobalt(II) complexes near the cross-over point.

But it does not resolve the problem of anomalous Curie-Weiss

behavior in that the curves of 1/X versus T calculated by

including spin-orbit coupling do not contain maxima and/or

minima as do the experimental curves. However, if in

addition the ligand field strc. *' is considered to be a

function of temperature, the experimental 1// versus T

curves could be reproduced (57).

Host of the complexes which show anomalous magnetic

behavior are either perchlorate or iodide salts. From the

statistical point of view, there should indeed be more

anomalous complexes with perchlorate and iodide anions be-

cause these salts are usually the easiest to prepare because

of their insolubility and therefore are considerably more

prominent.

EC"3 and Wilkins investigated the complexes of

0Co(terpyridine)2]2+ with chloride, bromide, iodide, and

perchlorate anions, finding their room-temperature magnetic

moments decidedly different (54). They found the bromide

monohydrate salt to exhibit anomalous Curie-Weiss behavior.

The others were not investi-*ted as a function of temperature










because their magnetic moments were thought to inUicate

normal high-spin or low-spin complexes.

The research rith which this dissertation is con-

cerned deals with various effects of the solid state on the

magnetic susceptibility of some complexes which are known

to be near the cross-over point of cobalt(II), the cross-

over point being defined as the point at which the 4T1 and
E term states have the same energy. Since the .;netic

behavior of anomalous cobalt(II) complexes has been measured

on solid compounds, with the exception of two solution

susceptibility measurements (54), there is the possibility

that the anomalies observed might be caused by effects of

the solid state. The purpose of this investigation, then,

is threefold: (1) to determine whether the variation of

the room-temperature magnetic moment as a function of the

anion, as in the case of [Co(terpyridine)2 2+, is an iso-

lated case or a general phenomenon; (2) to determine how

the anion effect is manifested as a function of temperature;

and (5) to determine whether the unusual magnetic behavior

observed is a result of an alteration of the stereochemistry

of the complex in the solid state.

Three series of cobalt(II) complexes incorporating

different ligands were chosen. Two of the ligands, ter-

pyridine and pyruvaldihydrazone (Structures I and II), co-

ordinate with cobalt(II) to produce anomalous salts (27,28,










54). These salts are bis(terpyridine)cobalt(II) bromide
monohydrate and tris(pyruvaldihydrazine)cobalt(II) bromide.

The third ligand, biacetyldihydrazone (Structure III), is

also known to produce a rather 1-2ge crystal field split-

ting; the complex tris(biacetyldihydrazone)cobalt(II)

iodide is reported to exhibit normal Curie-Weiss behavior

with a Weiss constant of 142 (55). A series of anions

was chosen with the intention of illustrating any effect of

size and charge on the magnetic susceptibility. It was de-

cided to employ X-ray diffractometry as a means of detecting

crystalline alterations as a function of temperature. The

entire investigation was centered, however, around proving

a solid state anion effect by temperature-dependent

measurements of the magnetic susceptibility by the Gouy

method.




HC H HC CH

% N Y HN N $ c N
NH N N NH2 H2N N N NH2


Structure III


Structure I


Structure II












EXPERIMENTAL PROCEDURES


Many of the following preparations are similar in

procedure. The differences in detail were found to be

necessary modifications in the general method for the

synthesis of the complexes. Therefore, each synthetic pro-

cedure is presented separately.

Pyruvaldihydrazone, PvdH.-Pyruvaldihydrazone was

made by a method similar to that previously reported (28).

Tris(pyruvaldihydrazone)cobalt(II) bromide,

[Co(PvdH)3]I2.-A solution of anhydrous cobalt(II) iodide

(3.21 g, 0.0100 mole) in a minimum volume of warm absolute

ethanol was added slowly with constant stirring to a solu-

tion of pyruvaldihydrazone (3.00 g, 0.0300 mole) in a

minimum volume of warm absolute ethanol. The green micro-

crystalline product which formed immediately was collected

on a sintered glass filter, washed with absolute ethanol,

and dried over PO 10 in vacuo. Yield, 85 per cent. Anal.

for CoC9H24N12I2: C, 17.63; H, 3.83; N, 27.42. Found:

C, 17.44; H, 3.86; N, 27.60.

Tris(pyruvaldihydrazone)cobalt(II) nitrate,

[Co(PvdH)3](NO )2.-This product was prepared by a method









analogous to that used for [Co(PvdH) ]I2 using cobalt(II)
nitrate hexahydrate. Yield of the dark green product was
90 per cent. Anal. calcd. for CoC9H24N1406: C, 22.36; H,

5.01; N, 40.57. Found: C, 22.47; H, 4.99; N, 40.62.

Tris(Dyruvaldihydrazone)cobalt(II) perchlorate,

[Co(PvdH) ] (ClO)2.-This green product was prepared by a

method analogous to that used for [Co(PvdH) ]I2 using

cobalt(II) perchlorate hexahydrate. Yield, 90 per cent.

Anal. calcd. for CoC9H24N12C1208: C, 19.36; H, 4.33; N,

30.11. Found: C, 19.18; H, 4.32; N, 30.20.

Tris(pyruvaldihydrazone)cobalt(II) tetraphenylboron,

[Co(PvdH)3][B(C6H5 )42.-A solution of anhydrous cobalt(II)
chloride (0.65 g, 0.0050 mole) in warm absolute ethanol
(25 ml) was added slowly with constant stirring to a solu-
tion of pyruvaldihydrazone (1.50 g, 0.015 mole) in warm
absolute ethanol (25 ml). The solution darkened immediately,
and after approximately one-half of the cobalt chloride

solution was added, a solution of sodium tetraphenylboron
(3.42 g, 0.0100 mole) in absolute ethanol (15 ml) was
stirred in and then the remaining cobalt chloride solution
was added. The dark green precipitate which formed was

subsequently collected on a sintered glass filter, washed
with hot absolute ethanol several times, then washed with
a solution of 40 ml of water and 10 ml of ethanol, and dried










over P4010 in vacuo. Yield, 90 per cent. Anal. calcd. for
CoC57H64N12B: C, 69.36; H, 6.54; N, 17.03. Found: C,
67.72; H, 6.50; N, 16.80.

Biacetyldihydrazone, BdH.-The following method is an

improvement over that followed by Busch and Bailar (7).

Biacetyl (43.0 g, 0.050 mole) was added slowly with constant
stirring to an excess of anhydrous hydrazine (65 g, 2.0
moles). The mixture was cooled in an ice bath, and the
product was collected on a sintered glass filter, washed
with cold absolute ethanol followed by ether, and dried
over P4010 in vacuo. Yield, 78 per cent.

Tris(biacetyldihydrazone)cobalt(II) bromide,

[Co(BdH)3]Br2.-A solution of anhydrous cobalt(II) bromide

(2.19 g, 0.0100 mole) in warm absolute ethanol (20 ml) was
added slowly with constant stirring to a warm solution of
excess biacetyldihydrazone (5 g, 0.05 mole) in 75 ml of
ethanol and 75 ml of methanol. The dark brown product which

slowly formed was collected on a sintered glass filter,
washed with absolute ethanol followed by ether, and dried
over P4010 in vacuo. Anal. calcd. for CoC12H30N12Br2: C,
25.68; H, 5.39; N, 29.95. Found: C, 25.89; H, 5.46; N,

29.73.

Tris(biacetyldihydrazone)cobalt(II) iodide,

[Co(BdH) ]I2.-This product was prepared by the method of









Stoufer and Busch (53). Anal. calcd. for CoC12H30N12:2
C, 22.00; H, 4.62; N, 25.65. Found: C, 22.19; H, 4.52;
N, 25.37.

Tris(biacetyldihydrazone)cobalt(II) nitrate,
[Co(BdH)3](N03)2.-This product was prepared by a method
analogous to that used for [Co(PvdH)3](N03)2 using biacetyl-
dihydrazone. Yield, 65 per cent. Anal. calcd. for
CoC12H30N1406: C, 27.43; H, 5.76; N, 37.32. Found: C,
27.57; H, 5.56; N, 37.30.

Tris(biacetyldihydrazone)cobalt(II) perchlorate,
[Co(BdH) ](C104)2.-This product was prepared by a method
analogous to that used for [Co(BdH)3](N03)2 using cobalt(II)
perchlorate hexahydrate. The green product was washed
thoroughly with warm absolute ethanol followed by ether.
Yield, 90 per cent. Anal. calcd. for CoC12H30N12C1208:
C, 24.01; H, 5.04; N, 28.00. Found: C, 24.25; H, 5.16;
N, 27.73.

Tris(biacetyldihydrazone)cobalt(II) tetraphenylboron,
[Co(BdH)3][B(C6H5)4]2.-This product was prepared by a method
analogous to that used for [Co(PvdH)3][B(C6H5)4]2 using
biacetyldihydrazone. Yield, 90 per cent. Anal. calcd. for
CoC60H70N12B: C, 70.03; H, 6.86; N, 16.33. Found: C,
68.53; H, 6.61; N, 16.11.









Bis(terpyridine)cobalt(II) chloride pentahydrate,
[Co(terpy)2]C12*H20.-This product was prepared by the method
of Hogg and Wilkins (34). Anal. calcd. for CoC30H22N6C1205:
C, 52.49; H, 4.70; N, 12.24. Found: C, 52.27; H, 4.80;
N, 12.07.

Bis(terpyridine)cobalt(II) chloride tetrahydrate,
[Co(terpy)2]C12.4H20.-This product was prepared by a method
analogous to that used for [Co(PvdH)3]I2 using anhydrous
cobalt(II) chloride and terpyridine. Yield, 65 per cent.
Anal. calcd. for CoC30H30N6C1204: C, 55.90; H, 4.52; N,
12.57, Found: C, 54.07; H, 4.34; N, 12.28.

Bis(terpyridine)cobalt(II) bromide monohydrate,
[Co(terpy)2]Br2-H20.-This product was prepared by the method
of Morgan and Burstall (39). Anal. calcd. for
CoC30H24N6Br20: C, 51.23; H, 3.44; N, 11.95. Found: C,
50.95; H, 3.59; N, 11.67.

Bis(terpyridine)cobalt(II) iodide monohydrate,
[Co(terpy)2]I2.H20.-This product was prepared by the method
of Morgan and Burstall (39). Anal. calcd. for CoC30H24N6I20:
C, 45.31; H, 2.79; N, 10.57. Found: C, 45.02; H, 2.91; N,
10.32.

Bis(terpyridine)cobalt(II) nitrate,
[Co(terpy)2](NO3)2.-This product was prepared by a method
analogous to that used for [Co(PvdH)3](N03)2 using









terpyridine. The yield of the brown product was about 60

per cent. Anal. calcd. for CoC30H22N806: C, 55.48; H,

3.41; N, 17.25. Found: C, 54.97, 54.98; H, 5.46, 3.65;
N, 16.93, 17.11.

Bis(terpyridine)cobalt(II) perchlorate,

[Co(terpy)2](C104)2.-This product was prepared by a method
analogous to that used for [Co(PvdH) ](C104)2 using ter-
pyridine. The light or-n-e-brown product was collected on
a sintered glass filter, washed with absolute ethanol
followed by ether, and dried over P4010 in vacuo. Yield,
80 per cent. Anal. calcd. for CoC30H22N6C120g: C, 49.74;

H, 5.06; N, 11.60. Found: C, 49.90; H, 3.20; N, 11.40.

Bis(terpyridine)cobalt(II) perchlorate monohydrate,
[Co(terpy)2](C104)2'H20.-A solution of Co(C104)2-6H20 (1.85

g, 0.0050 mole) in water (50 ml) was added slowly with
constant stirring to a warm solution of terpyridine (2.55

g, 0.010 mole) in equal parts of water, ethanol, and
methanol (30 ml total). The orange-brown product which

formed immediately was collected on a sintered glass filter,
washed with water, absolute ethanol, and ether, in that

order. It was dried over P.010 in vacuo. Yield, 90 per cent.

Anal. calcd. for CoC30H24N6C1209: C, 48.55; H, 3.26; N,

11.32. Found: C, 48.38; H, 3.14; N, 11.08.









Anoxic bis(terpyridine)cobalt(II) perchlorate mono-
hydrate, [Co(terpy)2](C104)2.H20.-This product was prepared
by decreasing the atmospheric pressure over bis(terpyridine)-
cobalt(II) perchlorate monohydrate. The anoxic compound is
darker in color than the compound exposed to air. Anal.
calcd. for CoC30H24N6C1209: C, 48.55; H, 3.26; N, 11.52.
Found: C, 48.67; H, 5.55; N, 11.13. (Analysis of this
compound was performed by Schwarzkopf Microanalytical
Laboratory, Woodside, N.Y.)

Bis(terpyridine)cobalt(II) tetraphenylboron,
[Co(terpy)2][B(C6H5)4]2.-To an aqueous solution of
[Co(terpy)2]C12-5H20 (1.5 g, 0.0019 mole) was added an
aqueous solution of sodium tetraphenylboron (1.2 g, 0.0038
mole). The mixture thickened immediately, and the addition
of a small amount of ethanol caused the formation of a light
orange very finely divided precipitate. The product was
collected on a sintered glass filter, dried overnight, and
then washed with absolute ethanol followed by ether. The
material was then dried over P4010 in vacuo. Yield, about
60 per cent. Anal. calcd. for CoC78H 9N6B: C, 81.24; H,

5.42; N, 7.29. Found: C, 79.17; H, 5.23; N, 7.58.

Bis(terpyridine)cobalt(II) sulfate dihydrate,
[Co(terpy)2]SO4*2H20.-A solution of cobalt(II) sulfate
heptahydrate (1.41 g, 0.0050 mole) in warm water was added
slowly with constant stirring to a mixture of hot water and










terpyridine (2.33 g, 0.010 mole). The mixture was heated

above the melting point of terpyridine (880C) for several

minutes while stirring cot' ed. The mixture was allowed

to cool and a small amount of unreacted terpyridine was

filtered off. The slow addition of acetone caused the

formation of very shiny red-brown crystals. The product was

collected on a sintered glass filter, and washed thoroughly

with hot absolute ethanol. 7_e product was recrystallized

several times by dissolving in methanol and then adding

acetone dropwise. The material was dried over P4010 in vacuo.

Anal. calcd. for CoC,0H26 N6S6: C, 54.80; H, 3.99; N, 12.78.

Found: C, 55.38; H, 4.60; N, 12.48.

All analytical measurements were made by Galbraith

Nicroanalytical Laboratories, Knoxville, Tennessee, unless

otherwise noted. The analyses of the three complexes con-

taining the tetraphenylboron anion and the one complex con-

taining the sulfate anion were not as close to the calculated

values as desired. Nevertheless, these compounds are in-

cluded because of the importance of the size of the tetra-

phenylboron anion and the charge of the sulfate anion.

The complexes containing terpyridine appear to be

stable in air. All of the complexes containing pyruvaldi-

" -razone or biacetyldihydrazone decompose in air, some

considerably more rapidly than others. Those with the

largest anions were the most stable.










Apparatus

Magnet

The magnetic susceptibilities were determined by the

Gouy method. The equipment has been described previously

(13). The magnet used was a Varian Associates Model V-40004

equipped with four-inch cylindrical pole pieces, separated

by an air gap of 2-1/4 inches. A Varian Associates Model

V-2301-A current regulator was used to provide a constant

current (+ 1 x 103 amp). The maximum field strength

attained was 6812 + 40 oersteds. The magnetic field was

calibrated by using water, solid nickel ammonium sulfate

hexahydrate, tris(ethylenediamine)nickel(II) thiosulfate

(16), and mercury(II) tetrathiocyanatocobaltate(II) (38).

Cryostat and temperature control

The cryostat and temperature control apparatus used

were of the basic design of Figgis and Nyholm (24,25).

Temperatures between 1000 and 4000 K could be controlled

with less than 0.1 degree fluctuation.

Sample tubes

Separate sample tubes were used for solution and

solid state measurements. For magnetic measurements of the

solids, a quartz tube, approximately 3.5 mm inside diameter

and approximately 19.0 cm in length, was suspended in the

cryostat from a semi-micro balance by a diamagnetic gold










chain attached to a tapered Teflon plug. The dir-:-nnetic

correction of the tube was measured as a function of the

temperature between 1000 and ^0 K. For solution magnetic

measurements, a pyrex tube, approximately 15.6 mm inside

diameter and approximately 21.0 cm in length, was suspended

from the balance into a large glass tube which protected

the sample tube from air currents. Measurements were made

on solutions of known concentration. The diamagnetic cor-

rection for the sample tube filled with pure solvent was

subtracted from the observed change in apparent weight.

Balance

A settler Model B-6 semi-micro balance of 0.01 mg

sensitivity was used to measure the force exerted by the

magnetic field upon the sample.

Spectrometers

The solid state electronic spectral measurements were

obtained by using a Cary Hodel 14 recording spectrophoto-

meter with a Cary Model 1411 Diffuse Reflectance Accessory.

Magnesium carbonate was used as the reference. Infrared

spectra were obtained using a Beckman Model IR-10 equipped

with sodium chloride optics and calibrated with polystyrene.

Both the Nujol mull and pressed potassium bromide pellet

technique were used.










Conductance apparatus

All conductances were measured using an Industrial

Instruments, Inc., Model RC-18 Conductivity Bridge and a

cell with a constant of 1.485 cm A constant temperature

of 25.OC + 0.010 was maintained by the use of a silicone

oil bath, regulated by a Sargent Thermonitor, Model SW.
_^
Concentrations of approximately 2 x 10-2 M in reagent grade

dimethyl sulfoxide were used. This dimethyl sulfoxide had
-7 -1
a conductance of less than 8 x 10 mhos cm-

X-ray diffraction apparatus

The X-ray diffraction patterns were obtained by the

use of a Phillips Electronic Instruments Recording Diffracto-

meter equipped with a copper target. A curved single crystal

monochromator was used to reduce fluorescence. Low tempera-

tures of approximately -500C + 50 were obtained by passing

a stream of gaseous nitrogen through a copper coil submerged

in liquid nitrogen and then onto the sample. Temperatures

of approximately +450C + 30 were obtained by passing gaseous

nitrogen through a heated copper tube and then onto the

sample.

Electron paramagnetic resonance spectrometer

The equipment used has been described previously (50).

A Varian Associates electron paramagnetic resonance spectro-

meter system, V-4502-14, was used. The system consists of

a V-4501 console, a V-4500-41A microwave bridge, a V-4500







22

100 Kc field modulation and control unit, a V-3601 twelve-

inch magnet, and a V-Fr2503 magnet power supply unit. A

V-4531 multi-purpose cavity was used in combination with a

variable temperature accessory V-4557.












RESULTS


Magnetic Measurements

The room-temperature magnetic moments of the solids

and their solutions prepared during the course of this

investigation are listed in Table 2. All magnetic measure-

ments were obtained at two different field strengths,

namely, 6812 and 5724 oersteds. The close agreement of the

magnetic moments at different field strer.uhs indicates

that metal-metal interaction does not exist in any of the

complexes (38). For solution magnetic measurements, con-

centrations of 0.020 molar in dimethyl sulfoxide or water

were used. The data given are averages of two or more

separate measurements on different portions of the same

solution. The solvent was dimethyl sulfoxide unless other-

wise noted.

The acetylacetonate complex of iron(III) was chosen

as a reference standard for the solution magnetic measure-

ments. It is an uncharged complex and consequently there

is no anion which might possibly affect the magnetic be-

havior. The magnetic moment of solid is reported to be

5.95 B.M. (10). The solution magnetic moment was found in
the present investigation to be 5.93 and 5.90 B.M. in two









TABLE 2
MAGNETIC MOMENTS OF SOLIDS AND SOLUTIONS AT ROCK ?'7 ERATURE


Complex

[Co(PvdH) ](NO )2
[Co(PvdH)3]Br2
[Co(PvdH)3 ]I
[Co(PvdH)3](C104)2
[Co(PvdH)3][B(C H5)4]2
iCo(BdH)3](N03)2
[Co(Bdi)3]Br2
[Co(BdH) ]I2
[Co(BdH) ](C104)2
[Co(BdH)3][B(C6H5)4]2
[Co(terpy)2](NO )2c
[Co(terpy)2]C12.4H20c
[Co(terpy)2]C12 5H20c
[Co(terpy)2]Br2 H20
[Co(terpy)2]I2'H20
[Co(terpy)2](C104)2
[Co(terpy)2](C10 )2.H20
[Co(terpy)2](C104)2-H20
anoxicc)


a b a
Peff )3eff Peff
4.10 4.11 4.78
4.23 4.23 4.73
4.41 4.40 4.84
4.50 4.49 4.74
4.40 4.40 4.81

3.04 3.03 4.62
4.26 4.26 4.57
4.07 4.07 4.61
4.34 4.34 4.59
3.61 3.61 4.65
2.96 2.96 3.29
2.41 2.41 3.31
2.51 2.52 3.21
2.61 2.61 3.27
3.30 3.30 3.51
4.05 4.04 3.35
4.21 4.20 3.40


I


3.84 3.83


b
Peff
4.80
4.70
4.83
4.72
4.79
4.59
4.54
4.54
4.57
4.65
3.23
3.29
3.18
3.25
3.49
3.31
3.35










Table 2 (cont'd
Solid Solution
Complex a b a -
Peff Peff Peff Reff

[Co(terpy)2]SO4 2H20C 2.98 2.98 3.25 3.23
[Co(terpy)2]3B(C6H5 )]2 5.23 3.25 3.21 3.20


aField strength = 6812 oersteds.
Field strength = 5724 oersteds.
CSolution moment in water.










independent measurements, indicat'.-- excellent precision of

measurement of the solution 7netic moments.

The room-temperature tic moment of each complex

in the solid state is in the r ion inter eiae between

normal high-spin and low-spin octahedral cobalt(II) magnetic

moments. In order to determine the possibility of a

Boltzmann distribution over 11 -h- and low-spin states, the

magnetic susceptibility of each complex was determined as a

function of temperature. The temperature r- qe was from

1100 to 3500K or the temperature at which sample began

to decompose. All susceptibilities were corrected for the

diamagnetic contribution of the ligands using Pascal's

constants, and of the anions, the metal ion, and the water

of hydration using experimentally determined values (52)

(see Appendix I).

The reciprocal of the corrected magnetic suscepti-

bility versus the absolute temperature are shown in Figures

1 through 19. Tables 3 through 12 contain susceptibility

and magnetic moment data for the complexes. The plots for

all [Co(PvdH) 32+ complexes (data for [Co(PvdH)3]Br2 taken

from reference (27)) are represented in Figure 20, for all

[Co(BdH) 12+ complexes in Figure 21, and for all [Co(terpy)2 2+

complexes in Figures 22 and 23. The broken lines represent

plots for ideal high- and low-spin cobalt(II) complexes

obeying the Curie-Weiss law with Weiss constants of 0























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corresponding to temperature-independent magnetic moments

of 4.9 B.M. (lower line) and 1.9 B.M. (upper line). Only

one compound, [Co(PvdH)] CB(C H5)4]2 with a Weiss constant

of 260, obeys the Curie-Weiss law over the entire '" oera-

ture range studied. Two compounds, [Co(BdH)3]I2 and

[Co(terpy)2](Cl04)2"H20, have been reported previously to

follow the Curie-Weiss law exhibiting rather high values of

the Weiss constant of 1420 and 650, respectively (55). How-

ever, the present investigation indicates that although

Curie-Weiss behavior is normal over a portion of each of the

curves, deviations occur at the upper temperatures. This

was detected by taking a greater number of measurements over

smaller temperature intervals.

In addition, the data here differ in part with those

reported by Hogg and Wilkins (34) on [Co(terpy)2]Br2 H20.

The general shape of the 1/Xversus T curves are similar,

but the values of the susceptibility reported are incon-

sistent within themselves in that the text data do not agree

with the listed data. There are other obvious errors in

the article (34).

Some differences in experimental values should not

be unexpected, however, in view of the extreme sensitivity

of the magnetic moment of anomalous complexes to the crystal

lattice (see Discussion). It has been reported previously

that small differences in the procedure of preparation can

be very important on the magnetic behavior (4).









The graphical presentations of the magnetic moments

as a function of temperature in Figures 24 through 27

illustrate the fact that none of the magnetic moments falls

below the low-spin octahedral cobalt(II) range nor above

the high-spin octahedral cobalt(II) range. All of the

magnetic moments are dependent upon the temperature.

It is interesting to note in Table 2 that the moments

of [Co(PvdH) ]2+, [Co(BdH)3]2+, and [Co(terpy)22+ in

solution are 4.77 + 0.10, 4.60 + 0.10, and 3.55 + 0.15 B.M.,

respectively. It was assumed that dissolving a complex in

a suitable solvent would remove any effects of the solid

state and the anion, if such effects were present. In that

the magnetic moments of identical cations in solution are

the same within experimental error, the assumption was a

valid one. The solution magnetic moments are therefore used

as reference standards from which deviations in the solid

state can be based.

X-Ray Diffraction Measurements


The X-ray diffraction patterns of compounds prepared

during the course of this investigation are illustrated

graphically in Figures 28 through 46. One compound, anoxic

[Co(terpy)2](C104)2.H20, could not be kept sufficiently free

of oxygen for its diffraction pattern to be obtained. For a

single complex at a given temperature the peak of greatest































CH N
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O a


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0
100


50


0
100


50

0





100


50


0
100


50


0
100


Fig. 29.- X-ray diffraction pattern of [Co(PvdH) ]I2
at three temperatures


3 4 5 6 7
d, A


8 9 10 11


-500







+250






+450
--.5




2 3 4 5 6 7 9 10 11 12
d, A
Fig. 28.- X-ray diffraction pattern of [Co(PvdH) ]Er2
at three temperatures

-500



1 I0






I I I I I
+250







+450







100


50


0
100


50


0
100


50
5o


0





100


50


0
100


50


0
100


50


0


2 3 4 5 6 7
d, A


8 9


10 11


Fig. 31.- X-ray diffraction pattern
at three temperatures.


of [Co(PvdH)3](N03)2


+450





2 3 4 5 6 7 o 8 9 10 11 12
d, A
Fig. 30.- X-ray diffraction pattern of [Co(PvdH) ](Cl10)2
at three temperatures


-500







+250







+450


- --- -- ----- ------







100


50


0
100


50


0
100


50


0





100


50


5o
0
100


50


0
100


2 3 4 5


6 7
d, A


Fig. 33.- X-ray diffraction pattern
at three temperatures


9 10 11


of [Co(BdH) 3Br2


68


S_500







+250

-I



----.----------
+450





2 3 5 6 7 o 8 9 10 11 12
d, A

Fig. 32.- X-ray diffraction pattern of [Co(Pvd)31 [B(C6H5)4 2
at three temperatures

-500







+250






+450
+450




i I Il--







100


50


0
100


50


o
100


50

o
0





100


50


o
0
100


50


0
100


3 4 5 6 7 8
d, A

Fig. 35.- X-ray diffraction pattern
at three temperatures


of [Co(BdH)3](C104)2


-500







+250




II I I I I

+450





2 3 4 5 6 7 8 9 10 11 1;
d, A
Fig. 34.- X-ray diffraction pattern of [Co(BdH)3]I2
at three temperatures


-500








lII II+2I

I -
















+250







+450



III I I I|
3 8 9 10 11 12
O
d, A

Fig. 36.- X-ray diffraction pattern of [Co(EdH) 3(NO )2
at three temperatures

-50






+25







+450




I I I 1 I I I


4 5


Fig. 37--


6 7
0
d, A


X-ray diffraction pattern
at three temperatures


8 9 10 11


of [Co(BdH)3][B(C6H5)4]2


50


0
o








50


0
100


50


0
100







100


lO100
-+250

0 0
00


100

550
S4450

50 -i

Q i I I I i I I
o
2 3 4 5 6 7 8 9 10 11 12
d, A
Fig. 38.- X-ray diffraction pattern of [Co(terpy)2]C12'5H20
at three temperatures


I I -500


*I R i


SI I i i I + I


+250


- --5-


II I 7 *


2 3 5 6
0
d, A


9 10 1 1
9 10 11 12


Fig. 39.- X-ray diffraction pattern of [Co(terpy)2]Cl124H20
at three temperatures


100


50


$ 0
U) 100
00
100


50
,r-0
+-0
- 0

100


50


0


-


-


+450


1 111







72


0
100


50


0
100


50


0





o
100


50


0
100


50


0
100


2 3 4 5 6 7 8
d, A
Fig. 41.- X-ray diffraction pattern
at three temperatures


9 10 11 1;


of [Co(terpy)2] I2H20


-500






+250







+450



-@

2 3 4 5 6 7 8 9 10 11 12
0
d, A
Fig. 40.- X-ray diffraction pattern of [Co(terpy)2]Br2.H20
at three temperatures


-500




SI I I


+250







-450




i I i I







100


50


io
0
100


50

o
0
100


2 3

Fig. 42.-


4 5 6 7 8
d, A
X-ray diffraction pattern of
at three temperatures


9 10 11 12

[Co(terpy)2] (C104)2H20


I 1 I I I I I I III I II ,[II ,


+250






+450
SI II






I i ,


2 3 4 5 6 7
d,
d, A


8 9 10 11 12


X-ray diffraction pattern of [Co(terpy)2](ClO4)
at three temperatures


+450


100


50


0
100


50


0
100


50


0


Fig. 43.-







100


50

o
0
100


50

0
o
100


50

0


2 3 4 5 6 7 8 9 10 11
d, A


Fig. 44.-


X-ray diffraction pattern of
at three temperatures


2 3 4 5 6


7
o
d, A


[Co(terpy)2 ][B(C6H5)4]2


8 9 10


11 12


Fig. 45.-


X-ray diffraction pattern of
at three temperatures


[Co(terpy)2]SO4*2H20


-500






+250






+450

-


100


50

o
0
100


50

0
100


+450
---__.-_______

















































2 3 4 5


6 7
0
d, A


8 9


10 11


Fig. 46.- X-ray diffraction pattern of [Co(terpy)2](N03)2
at three temperatures


-500




I I |


100


50


0
S100
4)

50


r- 0
100


50


0


+250


n i


+450




III I


-


-







-


I I









intensity is given a relative intensity of 100, upon which

value all other relative intensities are based. Relative

intensities less than 10 are generally omitted for reasons

of clarity. Since most structural calculations are based on

data other than d-spacings, a computer program was written

with the aid of David L. Williams to calculate values of

the angle theta, sine theta, sine2 theta, and the d-spacings

from the diffractometer measured value of two theta. The

data are presented in Appendix II.

The three temperatures at which the diffraction

measurements were made, -500, +250, and +45C, gave a wide

temperature range over which to observe possible changes

of the gross crystal structure. [Co(terpy)2]C12*5H20 and

[Co(terpy)2]C12-4H20 undergo changes in their patterns as

the compounds are heated from room temperature to 45. Al-

though their patterns differ at room temperature, they become

identical at 450. The most plausible explanation for the

crystal change is that some water of hydration is being lost

from each of the solids,with the result that both compounds

possess the same structure and the same number of water

molecules of hydration, if any, at +45. Pronounced struc-

ture changes are not apparent in any of the other complexes

prepared during the course of this investigation.

It was hoped that from the X-ray diffraction data the

complexes could be indexed according to crystal system, thus








77

enabling calculation of lattice parameters. Correlation of

changes of the lattice parameters as a function of tempera-

ture with the magnetic behavior of the solid could perhaps

yield valuable information concerning distortions as a

function of temperature. Unfortunately, indexing was not

successfully accomplished on the compounds because of the

low symmetry typical of many coordination compounds (1,19).

Conductance Measurements

The equivalent conductance of several complexes was

determined in dimethyl sulfoxide to detect the possible

formation of ion pairs as experimentally observed in dimethyl

formamide. Concentrations of 0.020 molar were used. The

values observed were 27.5, 28.5, and 23.6 cm equiv-1 ohm-1

for [Co(terpy)2](C104)2, [Co(BdH)3](C104)2, and

[Co(terpy)2]Br2.H20. In addition, the conductance of a

typical complex, [Co(terpy)2](Cl04)2, was measured over a

tenfold range of concentrations. The linearity of the plot

of equivalent conductance versus the square root of the

equivalent concentration indicates that the existence of ion
pairs in dimethyl sulfoxide is not an important factor in

the concentrations used in this investigation (5).










Spectral Measurements

Diffuse reflectance spectra of the complexes were

measured and the positions of the peaks and shoulders are

compiled in Table 13. Quantitative determinations of ab-

sorptivities are not possible with diffuse reflectance

measurements and therefore are not reported.

Unfortunately, cobalt(II) complexes incorporating a-

diimine coordinating groups seldom give informative resolved

spectra and therefore few interpretations have been reported.

An energy level diagram (Figure 47) for the d7 ion in an

octahedral field reveals that the three spin-allowed transi-

tions are from the 4T1( F) ground state to the excited

states T2' A2, and 4T1( P). The corresponding energies

are 0.8 A, 1.8 A, and 0.6 A + 15,400 cm-1, respectively (58).

It is difficult to assign electronic transitions in the

complexes prepared in this investigation according to this

scheme. For example, if the lowest energy absorption of

[Co(terpy)2 2+ complexes (15,000 cm- ) is assigned the T1
1
T2 transition, the calculated value for A would be

18,600 cm-1. On the other hand, if the lowest energy ab-

sorption is assigned the T1 -> A2 transition, the calculated
value of A would be 8,300 cm-1. Since the expected value of

A is in the vicinity of 14,000 cm-1 (28,55), the two assign-

ments normally possible are either unrealistically large or

small. Nevertheless, the solution spectrum of [Co(terpy)2]2+










TABLE 13

DIFFUSE REFLECTANCE SPECTRA AND ELECTRON PARAMAGNETIC
RESONANCE g VALUES


Complex Wavelength,
Ao


[Co(PvdH) ](NO )2


[Co(PvdH) ]Br2


[Co(PvdRH)3]I2


[Co(PvdH)3](C104)2


[Co(PvdH) ][B(C6H5)4]2


[Co(BdH) 3](N03)2

[Co(BdH) ]Br2


[Co(BdH)3]I2






[Co(BdH) ](C104)2

[Co(BdiH)3][B(C6H5)/4]2


9,200 sh
4,000
9,000
4,050

6,000 sh
3,400 sh

3,900
3,500
9,200 sh
4,000

3,900

8,750
4,000

12,000 sh
9,200 sh
6,200 sh
5,150
4,000

3,500 sh

3,500
4,000


Wave-
number
-1
cm

10,880
25,000

11,000
24,690

16,650
29,400

25,600
28,550
10,880
25,000

25,600

11,450
25,000

8,530
10,880
16,130
19,430
25,000

28,550

28,550
25,000


g
Value


2.14


2.13a


2.14


2.13


2.13

2.13


2.11a






2.09

2.09b









Table 15 (cont'd)
Complex Wavelength, Wave- g
A number Value
-1
cm


[Co(terpy)23](NO)2




[Co(terpy)2 ]C12"H20





.[Co(terpy)2]C12-5H20



[Co(terpy)2]Br2-H20





[Co(terpy)2]I2.H20





[Co(terpy)2](C104)2





[Co(terpy)2](C104)2*H20


6,700
5,550
5,050
4,000

6,700
5,550
5,050
4,500

6,700
5,500
4,700

6,700
5,550
5,150
4,500

6,700
5,600
5,100
5,700
6,700
5,550
5,100
5,600

5,500
5,100
5,600


14,920
18,000
19,800
25,000

14,920
18,000
19,800
22,200

14,920
18,180
21,500

14,920
18,000
19,400
22,200

14,920
17,850
19,600
27,000

14,920
18,000
19,600
27,800

18,200
19,600
27,800


2.11





2.08





2.09a



2.08a





2.06





2.11





2.06









Table 13 (cont'd)
Complex Wavelength, Wave- g
A number Value
-1
cm

[Co(terpy)2](Cl0o)2.H20 2.09
anoxicc)

[Co(terpy)2]SO0-2H20 7,200 13,900 2.06
5,600 17,850
5,100 19,600
4,500 22,200
3,550 28,200

[Co(terpy)2] B(C6H5)4]2 6,800 14,700 2.11b
5,550 18,000
5,100 19,600
4,500 22,200
3,250 30,800

aReference 50.
bAveraged over hyperfine splitting.






















2A A2 2A












A-1
47
4 2




2
ST



2G T.




F 1 / 2E




Fig. 47.- Energy level diagram for the d conr
in an octahedral field


figuration










indicate that the lowest energy absorption must be a d-d

transition because of its broadness and absorptivity index

(about 80). Similar difficulties are encountered in

attempting to assign the absorptions of [Co(PvdH) ]2+ and

[Co(BdH)3]2+ complexes.

The differences of the magnetic susceptibilities of

[Co(terpy)2]2+ complexes indicate that the cobalt(II) ion

experiences a wide range of ligand field strengths contin-

gent upon the anion in the crystal. This variation in the

ligand field strength should be reflected in the electronic

spectra (d-d transitions) of the complexes since both the

magnetic moment and the spectra result from the electronic

structure of the complex. The fact that the spectra ob-

served for the [Co(terpy)2] complexes are almost identical

suggests that the absorptions are due to charge transfer

transitions which are, to a first approximation, independent

of the ligand field strength. On the other hand, the room-

temperature magnetic moments of the complexes of the other

two series are more nearly the same; therefore, the d-d

transitions should occur at approximately the same positions.

The positions of the absorptions of lowest energy typical of

d-d transitions are not the same and consequently assignment

of these absorptions is tenuous.

Each complex reported herein displays an electron

paramagnetic resonance spectrum which is characteristic of









low-spin cobalt(II). The g values were calculated and are

presented in Table 13. All values lie in the vicinity of

2.10 + 0.04, within the range reported by Schmidt (50). It

is concluded that every compound reported in this investiga-

tion, even [Co(PvdH)-][B(C6H 5)]2 which exhibits normal

Curie-Weiss behavior, has a significant amount of low-spin

species present at liquid nitrogen temperatures. Thus, in

agreement with Schmidt (50), anomalous Curie-Weiss behavior

is not a requisite for the existence of a Boltzmann distri-

bution over spin states.












DISCUSSION


Theoretically, there has been little reason to believe

that a non-coordinated anion should have a significant effect

upon the magnetic behavior of a coordination compound. In

general, the crystal field spectra of inorganic complexes

are independent (to within approximately 2 per cent) of the

effect of anything outside the primary coordination sphere

(38). Since both spectra and magnetic characteristics are

intimately related to the electronic structure of the com-

plex, the magnetic moment should be similarly independent

of the effect of chemical species outside the primary co-

ordination sphere. It is significant, therefore, that the

anion of each complex prepared during the course of this

investigation has a marked effect upon the magnetic

susceptibility.

Dissolving the complexes in dimethyl sulfoxide or

water removed the effects of the crystalline lattice. The

solution magnetic moments observed were 4.77 + 0.10 B.M. for

the [Co(PvdH) ]2+ series, 4.60 + 0.10 B.M. for the [Co(BdH) ]2+

series, and 3.35 + 0.15 B.M. for the [Co(terpy)2]2+ series.

These moments indicate that the order of increasing ligand

strength for these three ligands with cobalt(II) is PvdE H










BdH < terpy. This order is reversed from the order with

nickel(II): terpy < BdH < PvdH, indicative of differences

of pi-bonding characteristics of the metal (38).

A few 1/X versus T curves have been reported previ-

ously for anomalous cobalt(II) complexes (27,28,44,53,54,55).

But the variety of curves has been increased considerably

by the work done in the present study (Figures 1 through 23).

Of the twenty complexes investigated, thirteen are reported

for the first time, and seventeen are shown, for the first

time, to exhibit anomalous Curie-Weiss behavior.

There are several possible explanations for the un-

usual effect of the anion. Considering the [Co(PvdH)] 2+

series, it is seen that the order of decreasing contribution

of the anion to the low-spin character of the complex is

NO > Br > I- > C10o B(C6 H)4-. It is immediately

apparent that this is also the order of increasing anion

size. The questionable ordering of NO- with respect to

size is reasonable if the planar D3h symmetry of the ion is

recalled. Whereas the other ions may be roughly considered

to be spherical ions, that is, little change in apparent

size by changing orientation, the effective size of the

nitrate ion along the D3 axis is less than that along one

of the C2 axes and is, in fact, less than the size of the

other ions. Thus, the variation of the magnetic suscepti-









2+
abilities of the salts of [Co(PvdH)3] +is correlated with

the size of the anion.

The order listed above follows, incidentally, the

order of the spectrochemical series (38). It must be pointed

out, however, that the spectrochemical series applies to

coordinated groups only. In all probability the anions of

the compounds reported herein are not coordinated. Indeed,

all available data indicate that pyruvaldihydrazone and bi-

acetyldihydrazone act as bidentate ligands (28,45) and that

terpyridine acts as a tridentate ligand (34,45). For ex-

ample, infrared spectra provide convincing evidence that

the anions are not within the coordination sphere. Non-

coordinated nitrate and perchlorate ions customarily exhibit
-1
strong absorptions between 1300 and 1400 cm1 and between

1050 and 1170 cm1, respectively (18,33). Upon coordina-

tion, however, the strong band of the nitrate ion is split

into two new bands, one lying at 1480-1530 cm1 and the

other at 1250-1290 cm1 ; the perchlorate band is similarly

split into two bands occurring at approximately 1200 and

1000 cm-1 (18,33). Splitting characteristic of coordinated

anions such as this is not observed in the nitrate and

perchlorate complexes prepared in this investigation.

[Co(PvdH)3](N03)2 and [Co(terpy)2]N03)2 have bands which
-i
are only slightly split, absorbing at 1372 and 1332 cm

&- 1341 and 1368 cm-1, respectively. The nitrate band of










[Co(BdH)3](NO )2 is unsplit, appearing at 1370 cm-1. All

the perchlorate salts prepared herein exhibit single broad
-1
absorption at approximately 1085 cm Thus, the infrared

data of the nitrate and perchlorate salts indicate distinct

non-coordinated ions by virtue of the positions of their

absorption maxima. Similar data are unobtainable for the

halide salts. But since the nitrate and perchlorate anions

represent the extremes of the anomalous magnetic behavior,

it is improbable that the halide salts, exhibiting inter-

mediate anomalous magnetic behavior, would lie within the

coordination sphere. Furthermore, if terpyridine were

acting as a bidentate rather than a tridentate ligand, this

would be evidenced in its infrared spectrum by a doubling

of its ring vibrations; such doubling was not observed.

Similar arguments obtain for the dihydrazone complexes.

The [Co(EdH)] ]2 system is similar to the [Co(Pvd~)3]2

system in several ways. Again a pronounced dependence of

the susceptibility upon the anion is noted. Excluding, for

the moment, the discussion of [Co(BdH) ](C100)2 at tempera-

tures below 1750K, it is observed that the anion order of

decreasing contribution to the low-spin character of the

complex is now KNO >B(C H5) > > Br C10~ This
6 65 4
order cannot be directly correlated with the size of the

anion as was done for the PvdH series. However, a rationali-

zation for this difference can be found from a detailed









examination of the X-ray diffraction patterns of these

complexes. Whereas the diffraction data of [Co(PvdH)3]Br2

and [Co(PvdH)3]12 have similar line positions, indicating

that these compounds are isomorphous, the complexes

[Co(BdH)3]Br2 and [Co(BdH) ]I2 are distinctly not iso-

morphous since the bromide salt has considerably more lines

than the iodide salt, denoting lower symmetry for this

crystal system. Thus, it is probable that the reversal of
2+
the bromide and iodide order relative to [Co(BdH) ]2+ arises

from the change in the crystal system. A similar circum-

stance exists with the tetraphenylboron salts.

Another exception to the size correlation is found

in the magnetic behavior of [Co(BdH)3](C100)2. Above 1750K

the complex behaves as expected, with the perchlorate anion

producing a small contribution to the low-spin character of

the complex; but, below 1750 the magnetic moment drops

sharply from 4.42 B.M. at 1750 to 2.68 BM. at 1550. As

evidenced by the crystal structure and magnetic character-

istics of [Co(BdH)3]I2 and [Co(SdH) ]Br2, it appears that

the crystal habit of the complex salt has an appreciable

influence upon its degree of low-spin character. According

to these observations, the unusual change in the 1/X versus

T curve of [Co(BdH) ](C10 )2 can be accounted for by a

change in the crystal habit of the complex from one of large

low-spin contribution to one of large high-spin contribution.










In order to fully substantiate this argument, it would be

necessary to measure the X-ray diffraction pattern before

and after the apparent change of phase. Unfortunately, the

low temperatures required for such measurement could not be

obtained by using the diffraction equipment available.

Similar observations concerning unusual magnetic behavior

resulting from an apparent change of phase have been re-

ported by Ewald et al. (21).

The data for the complexes containing terpyridine are

not quite so readily explained. The ordering of the anions

with respect to the degree of contribution to low-spin

character is more complicated in that there is a dependence

of the order upon the temperature. In addition to the

simple anion effect, there are effects arising from the

number of water molecules of hydration and adsorbed oxygen.

At room temperature the order of contribution of the

anion to the low-spin species is Cl~(4E20) > C1-(5H20)>

Br-(H20) > ,0N SO =(2E2O) > -(H20) > 3(C6E5),- (excluding

the perchlorate systems). Magnetic measurements made at

intermediate temperatures gave a rat'-r different order:

:,o- > C01(4H 20) 3r (H20) > C1-(5HE) > I(H20) >
SO =(2H20) > 3(C6H5)4~. The lowest temperatures at which

the measurements were made gave a still different order:

3r (H20) -T > Cl (4H20) > C1-(5H20) > I!(H20)>
r- (n2) > i 3-> -,











SO (2H20) >B(C6H5)7 o Thus, at no temperature can it be

said that the order strictly is the same as that observed

with the [Co(PvdH) ]2+ or [Co(BdH) ]2+ systems.
) 3
Several items here deserve further attention. It

has been shown in a concurrent investigation that anomalous

1/X versus T curves can be theoretically duplicated by

allowing the ligand field strength to be a function of

temperature (56). The observations concerning the relative

contributions of the nitrate and the bromide monohydrate

with respect to the degree of low-spin character of the

complex indicate that the change in the ligand field strength

over the temperature range studied is not the same in each

case. It is apparent from Figure 22 that the ligand field

strength of the nitrate complex is changing at a more rapid

rate than is that of the bromide monohydrate complex.

Furthermore, since the curves are so nearly identical over

a temperature range of approximately 1000, the sudden change

of the nitrate indicates that the change in the ligand field

strength with temperature is not uniform; rather, it is

variable. Ostensibly, both the amount of change in the

ligand field strength and its rate of change are very sensi-

tive to the crystal system and other undetermined solid

state effects.
2-1
The three [Co(terpy)2] perchlorate complexes are

quite illustratve of the extreme sensitivity of the magnetic




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