Title: Investigation of some tetragonally distorted cobalt (II) complexes
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Title: Investigation of some tetragonally distorted cobalt (II) complexes
Alternate Title: Tetragonally distorted cobalt II complexes
Physical Description: ix, 111 l. : illus. ; 28 cm.
Language: English
Creator: Ramirez, Oscar, 1940-
Publisher: s.n.
Place of Publication: Gainesville
Publication Date: 1965
Copyright Date: 1965
 Subjects
Subject: Cobalt   ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis - University of Florida.
Additional Physical Form: Also available on World Wide Web
General Note: Manuscript copy.
General Note: Vita.
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Bibliographic ID: UF00097908
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 - 000423998
oclc - 11062825
notis - ACH2403

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INVESTIGATION OF SOME TETRAGONALLY

DISTORTED COBALT(II) COMPLEXES





















By

OSCAR RAMIREZ, JR.










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, 1965












ACKNOWLEDGEMENTS

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 the author's Super-

visory Committee. For the patient guidance and encouragement

gi'.;n by Dr. R. C. Stoufer, the author expresses his sincere

gratitude.

The author wishes to thank Mr. Harold Fisher for trac-

ing mnnny of the figures in this manuscript, and Mrs. Edwin

Johnston who typed this manuscript.

The author gratefully acknowledges ohe support of the

National Aeronautics and Space Adm'u istration in the form of

a Traineeship for the academic year 1964-1965 and of the

National Science Foundation under Grant Number GP 1809 in

the form of materials and a Graduate Research Assistantship

.or the academic year 1963-1964.
















TABLE OF CONTENTS


Page


ACKNOWLEDGMENTS . .


LIST OF TABLES. . .


LIST OF FIGURES . .


INTRODUCTION. . . .


EXPERIMENTAL PROCEDURES


RESULTS AND DISCUSSION.


SUMMARY . . .


APPENDICES. . . .


BIBLIOGRAPHY. . . .


BIOGRAPHICAL SKETCH .


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* *


S. . . ii


. . . . iv


vii


* . .


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* . .


. . . . .


108

111


iii












LIST OF TABLES


Table

1. Specific Conductances at 25.0 C . .

2. Ultraviolet Absorptions. . . . . . .

3. Diffuse Reflectance Absorptions of Nickel(II)-
PAPI Complexes . . . . . . . .

4. Diffuse Reflectance Absorptions of Cobalt(II)-
PAPI Complexes . . . . . . .

5. Diffuse Reflectance Absorptions of Cobalt(II)-
PAT Complexes . . . . . . .


6. Assignments of Spectral Transitions of
Nickel(II)-PAPI Complexes. . . .

7. Assignments of Spectral Transitions of
Cobalt(II)-PAPI Complexes. . . .

8. Assignments of Spectral Transitions of
Cobalt(II)-PAT Complexes . . . .

9. Temperature Dependence of the Molar
Susceptibility and Magnetic Moment of
[CoC12(PAPI)]. . . . . . .

10. Temperature Dependence of the Molar
Susceptibility and Magnetic Moment of
[CoBr2(PAPI)]. . . . . . .

11. Temperature Dependence of the Molar
Susceptibility and Magnetic Moment of
[CoI2(PAPI)] . . . . . .

12. Temperature Dependence of the Molar
Susceptibility and Magnetic Moment of
[Co(NO2)2(PAPI)] . . . . .


* .


* 0


Page

18

25


45


44


46


.. 49


. 0


* 0







0 0



. 0










13. Temperature Depernence of the Molar
Susceptibility and Magnetic Moment of
[Co(CS)2(PAP )] . . . . . . .. 64

14. Temperature Dependence of the Kolar
Susceptibility and Magnetic Moment of
[Co(C10O)2(PAPI)]. . . . . . 65

15. Temperature Dependence of the Molar
Susceptibility and Magnetic Moment of
CoBr2(PAPI)(Green) . . . . . . .. 66

16. Temperature Dependence of the Molar
Susceptibility and Magnetic Moment of
[CoC12(PAT)2]. . . . . . . 67

17. Temperature Dependence of the Molar
Susceptibility and Magnetic Moment of
[CoBr2(PAT)2]. ...... . . . . 68

18. Temperature Dependence of the Molar
Susceptibility and Magnetic Moment of
CoI2(PAT) ] . . . . . . 69

19. Temperature Dependence of the Molar
Susceptibility and Magnetic Moment of
[Co(i02)2(PAT)2] . . . . . .. 70

20. Temperature Dependence of the Molar
Susceptibilit and Magnetic Moment of
[Co(NCS)2(PAT)2 . . . . . 71

21. Magnetic Moments of Cobalt(II) Complexes at
2980K and Curie and Weiss Constants. . . 80

22. Magnetic Moments of Nickel(II) Complexes . 81

23. Summary of A Values and Room Temperature
Magnetic Moments . . . . . .. 84
-1
24. Infrared Absorption Bands (cm- ) for
Cobalt(II)-PAT Complexes . .. . ... 9

25. Infrared Absorption Bands (cm ) for
Cobalt(II)-PAPI Complexes. . . . . 96


Page


Table







Table Page

26. Infrared Absorption Bands (cm- ) for
Nickel(II)-PAPI Complexes . . . . .. 100

27. Molar Susceptibilities of Ligands and Anions. 102

28. d-Spacings and Relative Line Intensities. . 103










LIST OF FIGURES


Figure Page
1. d-Orbital energy level diagram in an octahedral
Yield and in an axially compressed field. .. 3
2. Diffuse reflectance spectra of [NiBr2(PAPI)],
[NiI2(PAPI)], [Ni(H20)(PA)(PAPI)](Cl10)2, and
[NiCl2(PAPI)] from 3,000 to 7,000 A . . .. 30
5. Diffuse reflectance spectra of [NiBr2(PAPI)]
and CNiC12(PAPI)] from 6,000 to 13,500 A. . 31
4. Diffuse reflectance spectra of [NiI2(PAPI)] and
[Ni(H20)(PA)(PAPI)](C104)2 from 6,000 to
13,500 A. . . . . . . . . .. 32
5. Diffuse reflectance spectra of [CoI2(PAPI)],
[CoBr2(PAPI)], and [CoC12(PAPI)] from 5,000 to
7,000 A . . ... . . . .. .. 33
6. Diffuse reflectance spectra of [CoBr2(PAPI)],
[CoC12(PAPI)] and [CoI2(PAPI)] from 6,000 to
13,500 A. . . . . . . . . 34
7. Diffuse reflectance spectra of [Co(C104)2(PAPI)]
[Co(N02)2(PAPI)] and [Co(NCS)2(PAPI)] from
3,000 to 7,000 A. . . . . . . .. 35
8. Diffuse reflectance spectra of [Co(NO2)2(PAPI)]
[Co(C104)2(PAPI)], and [Co(NCS)2(PAPI)J from
6,000 to 13,500 A . . . . . . . 36
9. Diffuse reflectance spectra of green
CoBr2(PAPI) and green CoC12(PAPI) from 5,000 to
7,000 A . . . . . . . . .. 37


vii









Figure Page
10. Diffuse reflectance spectra of green
CoC12(PAPI) and green CoBr2(PAPI) from 6,000
to 13,500 A. . . . . . . .. . 38
11. Diffuse reflectance spectra of [CoBr2(PAT)2],
[CoI2(PAT)2] and [CoC12(PAT)2] from 5,000 to
7,000 A. . . . . . .. . . . 39
12. Diffuse reflectance spectra of [CoC12(PAT)2],
[CoBr2(PAT)2], and [CoI2(PAT)2] from 6,000 to
13,500 A . . . . . . . . . 40
15. Diffuse reflectance spectra of [Co(NCS)2(PAT)23
and [Co(NO2)2(PAT)2] from 3,000 to 7,000 A . 41
14. Diffuse reflectance spectra of [Co(NO2)2(PAT)2]
and CCo(NCS)2(PAT)2] from 6,000 to 15,500 A. 42
8
15. Partial energy level diagram for the d8
configuration in an octahedral field . . 48
16. Energy level diagram for the d7 configuration
in an octahedral field . . . . . 54
17. Temperature dependent susceptibility of
[Co(NO2)2(PAPI)], [Co(NCS)2(PAPI)], and
[CoC12(PAPI)] ..... .. . . 72
18. Temperature dependent susceptibility of
CCoBr2(PAPI)]. . . . . . . . 7
19. Temperature dependent susceptibility of
[CoI2(PAPI) . . . . . . . 74
20. Temperature dependent susceptibility of
CCo(C104)2(PAPI)]. . . . . . . 75
21. Temperature dependent susceptibility of green
CoBr2(PAPI). . . . . . . . 76


viii








Figure Page
22. Temperature dependent susceptibility of
[CoBr2(PAT)2] and [CoC12(PAT)] . . . 77
23. Temperature dependent susceptibility of
[Co(NO2)2(PAT)2] and [CoI2(PAT)2 . . .. 78
24. Temperature dependent susceptibility of
[Co(NCS)2(PAT)2]. . . . . . . . 79
25. Temperature dependent magnetic moment of
CCo(C104)2(PAPI)] . . . . . . . 86












INTRODUCTION


In general, six-coordinate compounds of cobalt(II)

exhibit high-spin magnetic moments (4.3-5.2 B.M.) (27).

There are, in contrast, few examples of six-coordinate

complexes exhibiting low-spin magnetic moments (1.8-2.0

B.M.) (15,27). However, compounds such as bis(2,6-

pyridindialdihydrazone)cobalt(II) iodide, 2.9 B.M., ex-

hibit magnetic moments which are too small for high-spin

complexes and too large for low-spin complexes. Complexes

exhibiting these intermediate moments are believed to be

near the cross-over between high-spin ( Tlg) and low-spin
(2E ) states (14,17,44).
-g
The characterization of the transition between low-

and high-spin states is one of the many intriguing problems

yet to be solved in the area of transition metal chemistry.

Few relevant examples exist and little is known of the

actual transition between these states. Recently, several

cobalt(II) compounds reported to exhibit unusual magnetic

behavior, have been discussed in terms of an equilibrium

mixture of several states characterized by different spin-

multiplicities (14,17,44). In most of these examples, the

ligands forming these complexes contain the dimethine link-

age, -N=C-C=N- .







2

It has been demonstrated that ligands containing the

dimethine linkage produce very large ligand field split-

tings in their six-coordinate cobalt(II) compounds (ca.

14,000 cm-1) (17,39); nonetheless, Griffith has estimated

the pairing energy for cobalt(II) in an octahedral environ-

ment to be 22,000 cm-1 (20). Liehr has estimated a value

of 16,300 cm1 (28); and Ballhausen has estimated a minimum

value of 15,400 cm-1; however there appears to be an error

in his calculation. Correcting his calculation gives a

minimum value of 17,500 cm-1 (2). Because these ligands

produce splitting considerably lower than the pairing

energy quoted by the above authors, it has been suggested

that a tetragonal distortion of some of these complexes may

be the factor causing pairing of electrons.

The assertion that a tetragonal distortion will

facilitate spin-pairing in these complexes is based on the

following crude extrapolations and observations (45).

A compression (increase in ligand field strength)

along the z-axis of an octahedral complex (Figure 1) will

increase the energies of the d 2 xz and dyz orbitals;

however, the energy of the d 2 orbital will be increased to
z
a greater extent than that of the latter two. To a first

approximation, the energies of the d 2 and dxy orbitals
x -y
will remain the same as in the regular octahedral environment.

It can easily be seen that the energy separation (A') which

















d d2 A
z


1 1 1d _L
22 z2 -y2
x -y x -y


nIi,"
-dy dxz
-xY -xz


.0 y xz


I y 11
-yz dxy


Fig. l.-d-Orbital energy level diagram in an octa-
Eedral field and in an axially compressed
field.


-yz


v










determines whether or not spin-pairing will occur in the

distorted complex is larger than that in the regular octa-

hedral complex.

An extension along the z-axis of an octahedral

complex produces, in the limit, a planar complex. Because

planar complexes of cobalt(II) containing unsaturated

nitrogen donor atoms are low-spin (2.1-2.9 B.M.), one

would expect a tetragonal distortion to favor pairing of

electrons.

The purpose of the investigations reported in this

dissertation was to test the above postulates by preparing

and characterizing a series of six-coordinate cobalt(II)

complexes in which the magnitude of a tetragonal component

is varied. The complexes are of the type, CoX2L2 and

CoX2L', where X is a monodentate ligand, L is 2-pyridinal-

p-tolylimine (PAT)* (Structure I), and L' is bis(2-

pyridinal)-o-phenylenediimine (PAPI)* (Structure II).

Several other metal complexes containing these ligands have

been prepared in order to facilitate the characterization

of the analogous cobalt(II) complexes.






These abbreviations will be used throughout this
dissertation.












H


CH / DN




Structure I


Structure II












EXPERIMENTAL PROCEDURES


2-Pyridinal-p-tolylimine, PAT.--This ligand was
prepared essentially in the manner given by G. Bahr and
H. Thamlitz (1) except that the product was not frac-
tionally distilled but merely recrystallized from hexane;

m.p. 57-580C.

Dichlorobis(2-pyridinal-p-tolylimine)cobalt(II),
CCoC12(PAT)2].--A solution of 2-pyridinal-p-tolylimine

(3.72 g, 0.019 mole) in absolute ethanol (approximately
25 ml) was added slowly with constant agitation to a solu-
tion of cobalt(II) chloride hexahydrate (2.58 g, 0.01 mole)
in absolute ethanol (approximately 25 ml). The orange-red
microcrystalline product which formed when placed on an
ice-bath was collected on a sintered glass filter under an
abundant flow of nitrogen, washed with a few ml of cold
absolute ethanol, and dried over P4010 in vacuo at 95C
for five hours.
Anal. Calcd. for CoC26H24N4C12: C, 59.79; H, 4.63;
N, 10.73. Found: C, 59.49; I, 4.52; N, 10.46. Yield 7.0 g.

Dibromobis(2-pyridinal-p-tolylimine)cobalt(II),
[CoBr2(PAT)2].--A solution of 2-pyridinal-p-tolylimine









(7.84 g, 0.04 mole) in absolute ethanol (approximately 25

ml) was added slowly with constant agitation to a solution

of cobalt(II) bromide (4.38 g, 0.02 mole) in absolute

ethanol (approximately 18 ml). The orange-red product

crystallized from the solution at room temperature, was

collected on a sintered glass filter under an abundant flow

of nitrogen, washed with a few ml of cold absolute ethanol,

and dried over P4010 in vacuo at room temperature.
Anal. Calcd. for CoC26H24N4Br2: C, 51.09; H, 3.96;

N, 9.17. Found: C, 51.18; H, 4.05; N, 9.19. Yield 11.3 g.

Diiodobis(2-pyridinal-p-tolylimine)cobalt(II),

ECoI2(PAT)2].--This product was prepared by a method analo-
gous to that used for [CoBr2(PAT)23, except that anhydrous

cobalt(II) iodide was used. A gummy material formed when

the solution was placed on an ice-bath. Upon addition of

excess concentrated aqueous potassium iodide solution with

stirring, the gum slowly crystallized. The orange product

was collected on a sintered glass filter under an abundant

flow of nitrogen, washed with several portions of distilled

water, and dried over P4010 in vacuo at 90C for about five
hours.

Anal. Calcd. for CoC26H24N4I2: C, 44.28; H, 3.45;

N, 7.94. Found: C, 43.95; H, 3.60; N, 7.81. Yield 8.3 g.








Dinitritobis(2-pyridinal-p-tolylimine)cobalt(II),

[Co(NO2)2(PAT)2].--A solution of 2-pyridinal-p-tolylimine

(7.84 g, 0.04 mole) in water was added slowly with constant
agitation to a solution of cobalt(II) chloride hexahydrate

(4.76 g, 0.02 mole) in water. A gummy material was formed
upon the addition of a solution of sodium nitrite (2.76 g,
0.04 mole) in water. Excess sodium nitrite solution was

added to the mixture with agitation. The gum slowly crystal-
lized. The orange product was collected and washed with

several portions of distilled water, and dried over P4010

in vacuo at 1000C for six hours.

Anal. Calcd. for CoC26H24N604: C, 57.45; H, 4.45;

N, 15.47. Found: C, 57.21; H, 4.51; N, 15.21. Yield 7.7 g.

Diisothiocyanatobis(2-pyridinal-p-tolylimine)-
cobalt(II), [Co(NCS)2(PAT)2].--This product was prepared by

a method analogous to that used for [Co(NO2)2(PAT)] except

that absolute ethanol was used as the solvent and potassium
thiocyanate was used in excess. A gummy material was formed
which eventually crystallized. The product was filtered,

dissolved in dimethyl formamide, refiltered, then recrystal-
lized by reducing the volume of the solution. The orange
product was collected, washed with absolute ethanol, and
dried over P4010 in vacuo at room temperature.
Anal. for CoC28H24N6S2: C, 59.25; H, 4.26; N, 14.81.
Found: C, 59.14; H, 4.24; N, 14.55. This complex can be









made more easily by using anhydrous cobalt thiocyanate and
following the procedure used for [CoBr2(PAT)]. Yield 5.7 g.

Dichloro[bis(2-pyridinal)-o-phenylenediimine]-

cobalt(II), [CoC12(PAPI)].--Five ml (0.055 mole) of 2-
pyridinecarboxaldehyde was added slowly and with constant

stirring under an abundant flow of nitrogen to a solution
(2.60 g, 0.02 mole) of anhydrous cobalt(II) chloride in
absolute ethanol (40 ml). To this solution was added a
solution of freshly sublimed o-phenylenediamine (2.16 g,

0.02 mole) in absolute ethanol (25 ml) with constant stir-
ring and under nitrogen. On continued stirring a butter-
scotch-colored product formed, which was collected on a
sintered glass filter under nitrogen, washed thoroughly
with absolute ethanol, and dried first at room temperature
over P4010 in vacuo, then at 1000C for six hours. The use
of nitrogen was a precautionary measure because these
complexes appear quite stable to oxidation in air.
Anal. Calcd. for CoC14H18N4C12: C, 51.95; H, 5.59;

N, 15.46. Found: C, 51.90; H, 5.50; N, 15.29. Yield 6.4

g.

Dibromo[bis(2-pyridinal)-o-phenylenediimine]-
cobalt(II), [CoBr2(PAPI)].--This rich brown product was

prepared by a method analogous to that used for [CoC12(PAPI)]
except that anhydrous cobalt(II) bromide was used.








Anal. Calcd. for CoC14H18N4Br2: C, 42.80; H, 2.79;
N, 11.09. Found: C, 42.90; H, 2.95; N, 11.19. Yield 7.5

g.

Diiodo[bis(2-pyridinal)-o-phenylenediimine]cobalt(II),
[CoI2(PAPI)].--This rust-colored product was prepared by a
method analogous to that used for [CoC12(PAPI)] except that
anhydrous cobalt(II) iodide was used.
Anal. Calcd. for CoC14H18N4I2: C, 56.09; H, 2.36;
N, 9.54. Found: C, 56.27; H, 2.54; N, 9.15. Yield 9.1 g.

Diisothiocyanato[bis(2-pyridinal)-o-phenylenedi-
imine]cobalt(II), [Co(NCS)2(PAPI)].--This straw-colored
product was prepared by a method analogous to that used
for [CoC12(PAPI)] except that anhydrou.s cobalt(II) thio-
cyanate was used.
Anal. Calcd. for CoC16H18N6S2: C, 52.06; H, 3.06;
N, 18.21. Found: 0, 52.21; H, 3.20; N, 18.14. Yield
5.4 g.

Diperchlorato[bis(2-pyridinal)-o-phenylenediimine]-
cobalt(II), [Co(C104)2(PAPI)].--This dark maroon product
was prepared by a method analogous to that used for
CCoC12(PAPI)] except that cobalt(II) perchlorate hexa-
hydrate was used.
Anal. Calcd. for CoC14H18N4C1208: C, 39.73; H,
2.59; N, 10.50. Found: C, 40.08; H, 2.70; N, 10.27.
Yield 9.0 g.










Dinitro[bis(2-pyridinal)-o-phenylenediimine]-
cobalt(II), [Co(NO2)2(PAPI)].--Three grams (0.044 mole) of
sodium nitrite were added to a solution (4.76 g, 0.02 mole)
of cobalt(II) chloride hexahydrate in a 3:1 ethanol:water
mixture (25 ml). All the sodium nitrite did not dissolve

but was kept in suspension by constant stirring. Five ml

(0.055 mole) of 2-pyridinecarboxaldehyde was added slowly
under an abundant flow of nitrogen and with constant stir-
ring to the above solution. To the resulting solution was
added slowly a solution of recrystallized (from chloroform)

o-phenylenediamine (2.16 g, 0.02 mole) in 3:1 ethanol:water
mixture (25 ml) with constant stirring under nitrogen. On
continued stirring a rust-colored product formed, which
was collected on a sintered glass filter under nitrogen,
washed once with 3:1 ethanol:water mixture, followed by a
thorough washing with 95 per cent ethanol, then with abso-

lute ethanol, and dried first at room temperature over
P4010 in vacuo, then at 100C for six hours.

Anal. Calcd. for CoC14H18N604 0 C, 49.44; H, 3.23;

N, 19.22. Found: C, 49.33; H, 3.35; N, 19.20. Yield 3.0

g.
Green dichloro[bis(2-pyridinal)-o-phenylenediimine]-
cobalt(II), CoCl2(PAPI).--This green product was prepared
in a manner analogous to that used by Petrofsky (37). Four

ml (0.042 mole) of 2-pyridinecarboxaldehyde was added to a









solution (2.16 g, 0.02 mole) of freshly sublimed o-phenylene-
diamine in absolute ethanol (25 ml) and the mixture was re-
fluxed for twenty minutes. To this previously cooled
solution was added a solution (4.76 g, 0.02 mole) of
cobalt(II) chloride hexahydrate in absolute ethanol (25 ml)
with stirring and under a flow of nitrogen. A dark green
gummy material was immediately formed which crystallized on

continued stirring. The product was collected on a sintered
glass filter under nitrogen, washed thoroughly with absolute
ethanol, and dried at 900C over P4010 in vacuo for six hours.

Anal. Calcd. for CoC14H18N4C12 H20: C, 49.73; H,

3.71; N, 12.89. Found: C, 49.63; H, 3.90; N, 12.72.
Yield 4.2 g.

Green dibromo[bis(2-pyridinal)-o-phenylenediimine]-
cobalt(II), CoBr2(PAPI).--This green material was prepared
in a manner analogous to that used for the green CoC12(PAPI)
except that anhydrous cobalt(II) bromide was used.

Anal. Calcd. for CoC14H18N4Br2: C, 42.80; H, 2.79;
N, 11.09. Found: C, 42.55; H, 2.99; N, 10.86. Yield 5.9

g.
Dichloro[bis(2-pyridinal)-o-phenylenediimine]nickel-
(II) sesquihydrate, [NiC12(PAPI).]*/2 H20.--This mustard-
colored product was prepared in a manner analogous to that
used for [CoC12(PAPI)] except that nickel(II) chloride hexa-
hydrate was used.









Anal. Calcd. for NiC14H18N4C12 3/2 H20: C, 48.80;
H, 3.87; N, 12.65. Found: C, 49.09; H, 4.00; N, 12.56.
Yield 5.0 g. After heating to 190C in vacuo over P4010
found: N, 12.81.

Dibromo[bis(2-pyridinal)-o-phenylenediimine]nickel-
(II) sesquihydrate, [NiBr2(PAPI)]-3/2 H20.--This tan
product was prepared in a manner analogous to that used
for [CoC12(PAPI)] except that anhydrous nickel(II) bromide
was used.
Anal. Calcd. for NiC14H18N4Br2 3/2 H20:: C, 40.65;

H, 3.20; N, 10.53. Found: C, 40.78; H, 3.40; N, 10.25.
Yield 6.1 g.

Diiodorbis(2-pyridinal)-o-phenylenediimine]nickel(II),
[Nil2(PAPI)].--This orange product was prepared in a manner
analogous to that used for [Co(NO2)2(PAPI)] except that
nickel(II) chloride hexahydrate and potassium iodide were
used.
Anal. Calcd. for NiC14H18N4I2: C, 36.10; H, 2.36;

N, 9.36. Found: C, 35.89; H, 2.57; N, 9.45. Yield 9.7 g.

Aquo-2-pyridinal[bis(2-pyridinal)-o-phenylenediimine]-
nickel(II) perchlorate, [Ni(H20)(PA)(PAPI)](C104)2.--This
rose-beige product was prepared in a manner analogous to
that used for [CoC12(PAPI)] except that nickel(II) perchlo-
rate hexahydrate was used.









Anal. Calcd. for NiC14H18N412: C, 36.10; H, 2.36;

N, 9.36. Found: C, 35.89; H, 2.57; N, 9.45. Yield 9.7 g.

AQuo-2-pyridinabis(2-pyridinal)-o-pheylenedi-

imine]nickel(II) perchlorate, [Ni(H20)(PA)(PAPI)](C104)2.--

This rose-beige product was prepared in a manner analogous

to that used for [CoC12(PAPI)] except that nickel(II)

perchlorate hexahydrate was used.

Anal. Calcd. for NiC20H21N 08C12: C, 43.08; H,

3.16; N, 10.47. Found: C, 42.96; H, 3.29; N, 10.58.

Yield 9.8 g.

All analytical measurements were made by Galbraith

Microanalytical Laboratories, Knoxville, Tennessee.

Apparatus

Magnet. The magnetic susceptibilities were deter-

mined by the Gouy method. The equipment has been described

previously (8). The magnet used was a Varian Associates

Model V-4004 equipped with 4 inch cylindrical pole pieces,

separated by an air gap of 2-1/4 inches. A Varian Associ-

ates Model V-2300-A power supply and a Varian Associates

Model V-2301-A current regulator were used to provide a

current constant to within + 1 x 10-3 amp. The maximum
field strength attained was 6860 gauss. The magnetic field

was calibrated by using water, solid nickel ammonium sul-

fate hexahydrate, and tris(ethylenediamine)nickel(II) thio-

sulfate (13).











Cryostat and temperature control. The cryostat and

temperature control apparatus used were of the basic design

of Figgis and Nyholm (16). Temperatures between 100 and

400K could be controlled with less than 0.1 degree fluctu-

ation (8).

Sample tube. A quartz sample 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 the tapered Teflon plug.

The diamagnetic correction of the tube was measured as a

function of the temperature between 100 and 4000K.

Balance. A Mettler 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. A Cary Model 14 Recording Spectro-

meter was used to determine the ultraviolet, visible, and

near infrared spectra of the complexes. The solid state

spectra were obtained by using a Cary Model 1411 Diffuse

Reflectance Accessory. Magnesium carbonate was used as the

reference. A Perkin-Elmer Corporation Model 137B Infracord

recording spectrometer was used to determine the infrared

spectra of the complexes.

Conductance apparatus. All conductances were

measured using an Industrial Instruments, Inc., Model RCM









15 Bl Serfass conductivity bridge and a cell with a
-1
constant of 1.485 cm All measurements were made at 25C

in absolute ethanol, using 10-3 M solutions. A silicone

oil bath, regulated by a Sargent Thermonitor, Model SW,

was used to maintain constant temperature. The absolute

ethanol had a conductance of less than 5 x 10 mho cm-.

X-ray diffraction apparatus. The x-ray diffraction

patterns were obtained by use of a Phillips Electronic

Instruments Recording Diffractometer equipped with a copper

target. A single crystal monochromator was used to reduce

fluorescent background.











RESULTS AND DISCUSSION


Conductance measurements

The specific conductances of the PAT complexes and

of the green CoBr2(PAPI) complex in absolute ethanol were

measured at 25C. The values obtained are reported in

Table 1. There was no apparent change in color upon solu-

tion of these complexes. The specific conductances of the

octahedral PAPI complexes videe infra) were not measured

because each of these complexes undergoes a pronounced

color change upon solution in the few solvents in which

appreciable solubility was exhibited. The absolute ethanol

used in these determinations had a specific conductance of

less than 5 x 10-7 mho cm-.

The complexes reported in this investigation have

been formulated either as four- or six-coordinate species.

Numerous examples of each type exist. Six-coordinate

complexes, under ideal conditions, should behave as non-

electrolytes, that is, the two uni-negative anions should

occupy the fifth and sixth coordination sites. However,

the observed conductances fall slightly below those

characteristic of a uni-univalent electrolyte. For in-

stance, tetraethylammonium bromide has a specific conduc-




















TABLE 1

SPECIFIC CONDUCTANCES AT 25.00C


Complex

[CoC12 (PAT) 2]

[CoBr2 (PAT) 2]

[Col2 (PAT) 2]

[Co (N2) 2 (PAT) 2]

[Co (NCS) 2 (PAT) 2]

CoC12(PAPI) green

CoBr2(PAPI) green


Specific conductance (10-3M)
micromho/cm

31.7

30.5

36.8

23.2



27.0*

32.2


*Value reported by Petrofsky (37).









tance in absolute ethanol of 44.0 pmho cm-1 in a 1 x 10-3

molar solution, a value which falls within the range (40-

50 ~mho cm- ) of specific conductances quoted for other

uni-univalent electrolytes in absolute ethanol (29).

The observed conductances of these complexes might

be explained on the basis of an ionic five-coordinate

complex; however, there is no compelling reason to formu-

late such an unusual coordination number for cobalt(II).

Rather, cobalt(II) is so labile, that it seems more reason-

able to assume that these complexes are six-coordinate in

the solid state and that upon solution they undergo partial

anion displacement by the solvent molecules. These conduc-

tances are not unique to ethanolic solutions of these

complexes. Indeed, similar observations have been reported

for related complexes in methanol (38) and in N,N-dimethyl-

formamide (37) and rationalized on the basis of anion

displacement by the solvent. Furthermore, infrared data

substantiate (see Vibrational Spectra) coordination of the

weakest coordinating anion, perchlorate, in the solid state.

Certainly it is reasonable to expect the stronger bases,

viz., C1~, Br-, N02-, etc., to be coordinated also to the

metal ion in the solid state.

Vibrational spectra

The infrared spectrum provides another useful tool

in the characterization of inorganic complexes. In this









investigation, differentiation between linkage isomers and

between ionic and coordinated anions was made possible by

using this technique.

The major portion of the spectra of the complexes

can be assigned to the constituent groups of the organic

ligand (see Appendix I). The infrared spectra of the two

PAPI series differ. This observation is expected because

in the green PAPI complexes the organic ligand is presumed

to be non-planar, acting either as a bi- or tridentate

ligand, whereas in the other series it is planar, serving as

a tetradentate ligand. Thus, the appearance or absence of

some bands in the spectra of the two series is expected on

the basis of symmetry differences; some bands become

allowed as others become forbidden, etc. Interactions be-

tween groups in the different conformations would also cause

differences in the spectra.

The complexes within a series containing halogen

anions exhibit the same characteristic spectrum not only

because the metal-halogen bond stretching vibrations do not

appear in the region which was studied, but also because

these complexes have similar structures and organic ligand

bond energies. On the other hand, the complexes containing

polyatomic anions are characterized by the vibrational

spectra of the anions superimposed upon the spectrum of the

remainder of the complex.









The changes in the infrared spectrum of the perchlo-

rate ion upon coordination have been extensively investigated

by Hathaway and Underhill (21). These conclusive investiga-
tions have been substantiated by Wickenden and Krause (47).
The uncoordinated perchlorate ion of Td symmetry
has two infrared active vibrational modes (21). One of

these occurs as a strong and broad band at approximately
,110 cm-1. The second band occurs at 650 cm-1, beyond the

range studied. The band at 950 cm- which is infrared for-
bidden is observed as a very weak absorption (21). The
coordinated (through one oxygen atom) perchlorate entity

has Cv symmetry. Upon reduction from Td to C3 symmetry,
the broad absorption band present in the ionic perchlorate

is split into two well-defined bands with maxima at 1200

and 1000 cm-1 (21). The originally forbidden infrared
absorption now appears as a strong band between 940 and
-1
890 cm1.
It was found that in [Ni(H20)(PA)(PAPI)](C104)2, the

perchlorate entity is ionic and exhibits the characteristic
broad absorption with a maximum at approximately 1085 cm-1
and the weaker absorption at 950 cm-1. In [Co(C104)2(PAPI)],
however, the perchlorate entity is coordinated and exhibits
two strong bands with maxima at ,110 and ,035 cm-1 and a

somewhat weaker band at 920 cm1. The fact that the

perchlorate ion is coordinated in this complex is very im-
portant in this investigation (see Magnetic Measurements).









The SON group may coordinate through either the
nitrogen atom or the sulfur atom -- or through both (forming

a bridged species). In the first instance the group is

referred to as isothiocyanato and in the second, as thio-

cyanato. Various investigators have studied the effect of

linkage isomerization on the C-S stretching frequency (5,6,

7,26,40,46). It is observed that the C-S stretching
frequency is shifted to higher wave numbers in the spectra

of isothiocyanates and to lower wave numbers in the spectra

of thiocyanates, both relative to the C-S stretching

frequency of "ionic" KSCN (749 cm-1). Turco and Pecile

give the following ranges for the C-S stretching vibration:

M-SON, 690 720 cm-1; M-NCS, 780 860 cm-1 (46). Accord-

ing to Chatt and Duncanson, the CON vibration of the group

acting as a bridge absorbs near 2,182 150 cm-1, whereas

this vibration occurs at lower wave numbers in non-

bridging groups (7).

The infrared spectrum of [Co(NCS)2(PAPI)] exhibits
11
a weak absorption at 800 cm-. There are no absorptions in

the 690 720 cm-1 region. Furthermore, this absorption at

800 cm-1 does not appear in the spectra of the other PAPI

complexes, so it may be assumed that this is the C-S ab-

sorption, thereby indicating that it is the nitrogen atom

which is attached to the metal ion. The C=N absorption

appears at about 4090 cm-1 indicating that the group is not









bridging. The C=N absorption appears to be less sensitive

to linkage isomerism than is the C-S absorption; however,

an extensive tabulation of CEN absorption maxima reported

by Burmeister and Basolo indicate that the majority of C=E

absorptions of isothiocyanates fall slightly below 4100 cm-1;

whereas, the CEN absorption of thiocyanates mainly fall

slightly above 4100 cm-1 (5).

The spectrum of ECo(NCS)2(PAT)2] does not contain a

C-S absorption in either characteristic region. There are

four absorptions, common to all the PAT complexes, between

830 700 cm- which probably obscure the C-S vibration.
The CEN absorption appears at ,090 cm-1 (non-bridging).

It is unfortunate that the infrared spectrum could not be

more conclusive for this complex; it may still be assumed

quite reasonably, however, that the nitrogen atom is attached

to the metal ion. In support of this conclusion, Nakamoto

states that it is known from x-ray analysis that metals of

the first transition series form M-N bonds; whereas those

of the second half of the second and third transition series

form M-S bonds with the thiocyanate group (33).

The infrared spectrum of [Co(NO2)2(PAPI)l is con-

sistent with that of a nitrito complex, that is, coordina-

tion of the NO2 group through oxygen. Nakamoto lists the

symmetric stretching vibration of the nitrito group at

approximately 1065 cm1 and that of the nitro group at









approximately 1325 cm- (33). The absorption maximum of

the NO2 group in the spectrum of the above complex appears

at 1135 cm-.

The infrared spectrum of [Co(NO2)2(PAT)2] also indi-

cates that the oxygen is coordinated to the metal. The

absorption maxima of the symmetric stretching vibration of

the nitrito group in the spectrum of this complex appears
-1
at 1070 cm-.

Electronic spectra

The ultraviolet spectra of the PAT and the green

CoBr2(PAPI) complexes in absolute ethanol were recorded.

The absorption maxima and corresponding absorptivity co-

efficients are reported in Table 2.

The very intense absorptions in the region from

2,000 A to 3,500 A are usually due to transitions between

the energy levels of the ligand or between the energy

levels of the metal ion and the ligand (25,34,35). But,

few definite assignments of absorptions by compounds con-

taining complex ligand systems have been made in this

region. Unless one has made a detailed study of the energy

levels in a complex, assignment of specific transitions

is very difficult. Nonetheless, variations in the spectra

of similar complexes may often be interpreted in a quali-

tative manner.











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The transitions within the ligand usually involve

the pi system. The pi system of the ligand may or may not

be involved in the formation of bonds with the metal ion

upon complexation. If they are not involved, the spectrum

of the free ligand will be essentially unchanged upon

complexation. On the other hand, if they are involved, the

spectrum of the complex may be considerably different from

that of the free ligand. This behavior may be a useful

criterion for determining the degree of ligand-metal inter-

action in some of the complexes reported in this investi-

gation.

The ultraviolet spectra of PAT and [Co(PAT)3]I2.3H20

have been reported by Stoufer (43). Stoufer found that the

spectrum of the tris-complex was essentially the same as

that of the free ligand. This behavior was observed also

for the bis-complexes of PAT reported in this present

investigation. The very intense absorption at 2,175 A in

the spectrum of the [CoI2(PAT)2] complex is attributable

to a charge transfer transition between the iodide ion and

the solvent (35). This absorption is so intense that it

probably masks the weaker absorption at approximately

2,400 A appearing in the PAT complexes which do not contain

iodide ion. Since the spectra of the complexes were found

to be essentially the same as that of the free ligand, it

may be concluded that the ligand pi system is not involved

greatly in bonding with the metal.









Despite repeated attempts by this investigator and

by Petrofsky (57), the free PAPI ligand could not be iso-

lated. However, a solution spectrum, presumably of this

ligand prepared in situ was recorded by Petrofsky (37).

The spectra of the two green complexes do differ from that

of the free ligand. The absorption at 2,480 A in the free

ligand spectrum appears to be shifted to shorter wavelengths

in the spectrum of the coordinated ligand; whereas the

absorption at 2,950 A is shifted to longer wavelengths. The

absorption at 2,550 A is split into two bands, both appear-

ing at slightly longer wavelengths. These shifts and

splitting of the absorption maxima may be attributable to

pi interaction with the metal, as mentioned above; but in

this particular situation this may not be the only reason

for a change in the spectrum upon complexation. The free

ligand can exist in a number of conformations which are

distinct from that of the coordinated ligand. A change in

conformation could alter the pi system and, thereby, the

ultraviolet spectrum.

A Stuart-Briegleb model of the free ligand shows that

there is some interaction between the adjacent hydrogen

atoms on the pyridyl and phenyl groups. This interaction

tends to force the ligand out of a square planar conforma-

tion. It is believed also videe infra) that the cobalt(II)

ion in each of the two green PAPI complexes is four co-

orlinate, the ligand assuming a non-planar conformation






29

and acting as either a bidentate or tridentate ligand. The

most stable conformation of the free ligand may well remain

the same upon coordination, in which case the change in

the ultraviolet spectrum is attributable to participation

of the pi system in metal-ligand bonding rather than to a

change in conformation. Therefore, further investigation

is required before the observed behavior can be explained

more definitely.

The diffuse reflectance spectra of the complexes were

recorded from 13,500 A to 3,000 A and are shown in Figures

2 through 14. A list of the absorption maxima and shoulders

is given in Tables 3, 4, and 5.

The visible spectra of nickel(II) complexes have

been interpreted in terms of the ligand field theory by

many investigators (4,18,30,31,36,39). The absorption

maxima exhibited by the spectra of these complexes usually

agree very closely with ligand field predictions. Further-

more, these maxima are better defined than are those for

other complexes. For this reason, the spectra of nickel(II)

complexes have been very useful in the determination of A

values for a great variety of ligands. Thus, the nickel(II)

complexes reported in this investigation were prepared to

obtain an independent evaluation of relative ligand field

strengths.











































































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TABLE 3


DIFFUSE REFLECTANCE ABSORPTIONS OF NICKEL(II)--PAPI COMPLEXES

Complex Wavelength, A Energy, cm-1


[NiC12(PAPI)] 3/2H20





[NiBr2(PAPI)].3/2H20






[Nil2(PAPI)]






[Ni(H2I) (PA) (PAPI)] (C104)2


3,440
3,670
5,620
8,120
9,440

3,450
3,810
4,870
5,500
8,100
9,250

3,500
3,800
4,070
4,300
8,250
10,500

3,120
3,370
3,570
3,900
4,370
5,130
8,130
9,370


(sh)
(sh)


(sh)
(sh)


29,100
27,200
17,800
12,300
10,600

29,000
26,200
20,500
18,200
12,300
10,800

28,600
26,300
24,600
23,300
12,100
9,500

32,000
29,700
28,000
25,600
22,900
19,500
12,300
10,700


(sh)

(sh)


(sh)
(sh)
(sh)

(sh)








TABLE 4

DIFFUSE REFLECTANCE ABSORPTIONS OF COBALT(II)--PAPI COMPLEXES


Complex Wavelength, A Energy, cm-1


[CoC12 (PAPI)]








[CoBr2(PAPI)]










[Col2(PAPI)]






[Co (NO2)2 (PAPI) ]





[Co (NCS) 2 (PAPI)]





[Co (C104)2 (PAPI)]


3,340
3,590
3,950
4,630
5,500
6,090
7,500
12,750

3,300
3,550
3,800
4,070
4,750
5,620
6,250
7,250
12,370

3,530
4,500
5,125
5,770
7,750
11,120

3,440
4,190
5,500
7,000
12,880

3,000
5,580
6,350
7,130
10,380

3,300
3,550
3,900
5,090
5,960
6,560
11,000


(sh)

(sh)
(sh)

(sh)





(sh)
(sh)

(sh)
(sh)




(sh)

(sh)


30,000
27,900
25,300
21,600
18,200
16,400
13,300
7,800

30,300
28,200
26,300
24,600
21.100
17,800
16,000
13,800
8,100

28,300
22,200
19,500
17,300
12,900
9,000

29,100
23,900
18,200
14,300
7,800

33,300
17,900
15,700
14,000
9,600

30,300
28,200
25,600
19,600
16,800
15,200
9,100


(sh)
(sh)
(sh)










TABLE 4 Continued


Complex Wavelength, A Energy, cm-1


CoC12(PAPI) (green)


CoBr2(PAPI)


3,500
5,200
6,120
6,370
6,520
6,700
7,000

3,500
5,500
6,200
6,440
6,680
6,940
7,300


(Green)


(sh)


(sh)

(sh)


28,600
19,200
16,300
15,700
15,300
14,900
14,300

28,600
18,200
16,100
15,500
15,000
14,400
13,700


(sh)


(sh)













TABLE 5

DIFFUSE REFLECTANCE ABSORPTIONS OF COBALT(II)--PAT COMPLEXES


Complex Wavelength, A Energy, cm-1


[CoC12 (PAT)2]




[CoBr2(PAT)2]







[Co12(PAT)2]




[Co (NO2)2 (PAT)2]


[Co(NCS) 2 (PAT)2]


4,120
5,380
6,250
10,500

4,000
5,250
6,400
6,670
7,100
7,770
9,900

4,120
5,750
7,880
11,500

3,500
9,750

3,850
5,000
6,200
10,600


(sh)



(sh)







(sh)


24,300
18,600
16,000
9,500

25,000
19,000
15,600
15,000
14,100
12,000
10,100

24,300
17,400
12,700
8,700

28,600
10,300

26,000
20,000
16,100
9,400


(sh)
(sh)








The energy level diagram for a d ion in an octa-

hedral field (Figure 15) indicates that three spin-allowed

transitions should be observed, namely, from the 3A ground
-2g
state to the excited states 3 T, and T (3P). The
2g' 1 1 g a
energy separating the ground state from the first two ex-

cited states is A and 1.8 A, respectively. The energy from

the ground state to the third excited state is dependent

upon the multiple separation between the 3F and 3 terms

which varies considerably as the degree of covalent bonding

between the ligand and the metal ion varies. Robinson et al.

have observed that this third transition is obscured by

intense charge transfer bands in complexes formed ligands

containing the dimethine linkage (39). In addition to the

three spin-allowed transitions noted above, the spin-

forbidden transition ( A -- 1E) is frequently observed

(17,39).

Assignments of the transitions recorded in Table 6

were made on the basis of internally consistent ligand field

energy separations and previous observations.

The A values exhibited by the nickel(II) complexes

discuss" herein (Table 6) are considerably smaller than

those exhibited by nickel(II) complexes which are coordi-

nated with six unsaturated nitrogen atoms (17,39). This

observation is in accordance with the principle of an average

,-vironment (24) which is given by the formula,


























1





15 __________________A
1 -



Fig. 15.-Partial energy level diagram for the d
configuration in an octahedral field.









C
C

C
'-.


t3 to 0 00 to MW
HT? HI P I 4 P r I HI H|4
ce .-i cn cm r-4 ce) -4 1 -4 c1 cn

T T T T A T A




C4 C1 C-fI fCN C-f C-

n en en ) C) en

c.o
H



I

'-i


P-,
H







z


1--







c-o


0








H


0 0
00
tC ,-4

















2
1-

































I.4
Z
:2


O O O O






















0
--i









0
o Cr C



























NJ
-:1





C



.-4


C
cN
z


0 C C 0

0 0 00 o
o eJ co -
-4 1-4 -4 (N


0 0 0
o C Co
Cn cn 00

o c' r-l
1-4 4 -










A"AnB6-n = nAA6/6 + 6-nAMB6/6 ,

where AMA,6 and AMB6 represent the field strengths character-

istic of purely hexacoordinated species. Thus, the smaller

basicities of the anions in these complexes relative to

those of unsaturated nitrogen atoms serve to decrease the

average value of A.

Aside from the over-all decrease in the field

strengths, the ligand fields produced by the halide ions

with nickel(II) and cobalt(II) are expected to increase in

the order I < Br < Cl (class a metal behavior) because of

the positions of the halide ions in the spectrochemical

series. Contrary to expectations, the ligand fields ex-

hibited by the nickel-halide complexes reported here in-

crease in the reverse order (Table 6). This observation,

however, is not totally without precedence. Melson and

Busch found also that within a series of tetragonally dis-

torted complexes the iodo complex exhibits a larger A value

than does the chloro or bromo complex (32). The chloro

complex, however, exhibited a A value slightly larger than

that exhibited by the bromo complex. They attributed the

small fields produced by the chloro and bromo complexes to

a reduction of the ligand fields caused by an interaction

of the chloride ion and the bromide ion with the molecule

of water present in each of the complexes, that is, water

is hydrogen bonded between ions. Both the chloro and bromo









complexes contained a molecule of water which could not be

removed without decomposition of the complex.

The chloro and bromo complexes prepared during the

course of this investigation also contain water which can

not be removed in vacuo at 2000C over P4O10. Because of

this similarity in constitution between these complexes and

those reported by Melson and Busch, the observed ligand

field trends can be rationalized also in terms of hydrogen-

bonded water; however, doubt is cast on this explanation

by the fact that the octahedral cobalt(II)-PAPI-halo

complexes which do not contain water exhibit a similar

ligand field trend (Table 7).

An alternate explanation of the observed behavior

may be based upon a reversal in the metal character, that

is, becoming a class b metal. Upon coordination, the ligand

may donate sufficient electron density to the metal which

can in turn back-donate some of this electron density to

the ligand d-orbitals. For class b metals, the strength

of the metal-halide bond varies in the order I > Br > C1.

This order is due to the relative energies of the d-orbitals

which accept the back-donation and thereby form a second

bond. The d-orbitals which are closer in energy to that of

the metal orbital, form the stronger bond.

Examples exist for such a reversal in metal character.

Ferrous chloride, for example, will not coordinate with









carbon monoxide; however, coordinated ferrous ion (hemo-

globin) forms very strong bonds to carbon monoxide. This

strong bond has been explained on the basis of additional

bonding between the metal and the carbon monoxide resulting

from a back-donation of electron density from the metal to

the antibonding orbitals on the ligand. The same situation

may exist with the nickel(II) (and cobalt(II), vide infra)

complexes. However, further investigation is required

before a more definite assertion can be made.

The 2riplet-singlet transition in the spectra of the

nickel(II) complexes was observed as ill-defined shoulders

on the low energy absorption band. This position of the

transition conforms to observations reported by Robinson

et al., that is, it appears on the high energy side of the

band for A values below 12,100 cm1 and on the low energy

side for higher values (39).

The absorption attributed to the 3A .3Tg transi-
-2g -lg
tion appears as a very slight shoulder on the intense charge

transfer band which trails down across the visible region

from the ultraviolet. This absorption in the spectra of the

bromo and the perchlorate complex appears to be split. It

coul& not be ascertained whether or not this splitting was

due to a larger distortion within these complexes. In fact,

the chloro complex which exhibits essentially the same A

value as that by the bromo complex does not manifest any

splitting of this absorption.









The visible spectra of cobalt(II) complexes have

not been interpreted as completely as have those of the

analogous nickel(II) complexes. The absorption maxima are

less well defined and furthermore, the maxima do not con-

form as closely to the ligand field predictions. The energy

diagram (Figure 16) for a high spin d_ ion shows that three

transitions should be observed, namely, from the ground

state 4T1g to the excited states T 2g, 4A2g and 4Tlg(4 ),
-1
the energies corresponding to 0.8 A, 1.8 A, and 15,400 cm1
-l
+ 0.6 A, respectively. The value, 15,400 cm- is the

multiple separation between the F and P states of the

free ion; this value will be somewhat smaller in the

completed ion due to covalent bonding effects.

The assignments which were made for some of the

transitions are listed in Table 7. The octahedral PAPI

complexes containing halide ions exhibit the same ligand

field trend as that exhibited by the nickel-halo complexes.

The A values exhibited by the nickel(II) complexes, however,

are somewhat larger than those of the corresponding cobalt(II)

complexes. This observation is contrary to that which has

been observed previously. The pronounced absorptions in

the spectrum of the perchlorato complex are suspected of

being due to transitions between doublet states; however,

no definite assignments can be made. Definite assignments

of many of the remaining absorptions in the spectra of the

complexes can not be made.

























E

2G
4 P


4F 1





Fig. 16.-Energy level
ration in an


A ->


diagram for the d configu-
octahedral field.











Co 0 0 0
o a a a1
00 r-4 cJ 0o a
m g 0 0 a c
1-1 1-4


I I
I I
I I














FI 1
'- v-


bo ba ba bo bo o b
-4 -4j









Ell E PI Ell H


O





I
I

v




O







HQ H

U
WH
Cl|



vl


co~ ~ -4 0 co *c 0-
r"00000












a4 W-









P4 0)40

%- %-., .,
cq CI4 %-., -


.-, '- F -4 %- 0
C" J CNI '- I -
1-4 1d c'J Z Z 0 c' ~

0 0 0 0 0 0 0 pq
0 0 0 0 0 0 -4 0









The spectra of the two green PAPI complexes are

characteristic of tetrahedral complexes, that is, the

intense multicomponent absorption near 6,500 A (Figure 10)

is characteristic of tetrahedrally coordinated cobalt(II)

and is assigned, therefore, to the transition A -->
2g
ST1g( P) (3,22,23). This absorption lies at longer wave-

lengths in the bromo complex than in the chloro complex,

consistent with the behavior noted previously (9,10,11,12,

19,41). The pure iodo complex of this tetrahedral PAPI

series was never obtained; but, a reflectance spectrum of

the impure material exhibits the characteristic absorption

at still longer wavelengths. These data provide strong

evidence that at least one of the two halide ions is co-

ordinated to the metal. If a halide ion were not coordi-

nated, the position of this absorption should be unchanged

within the series of complexes.

Interpretation of the visible spectra of the PAT

complexes is made difficult by the fact that cis-trans

isomers can exist within the series of complexes. The

spectra of a cis-complex should exhibit a characteristic

broadening of the absorption maxima, whereas, the spectra

of a trans-complex should exhibit a splitting of some

absorption maxima. With a mixture of these isomers, there-

fore, the resultant spectrum would probably be poorly

defined with broad maxima. This behavior was observed in









the spectra of the PAT complexes. An intense charge

transfer absorption which trails across the visible region

from the ultraviolet also obscures some of the absorption

maxima. Nonetheless, some spectral assignments are listed

in Table 8.

The bromo complex has an intense absorption at

approximately 7,000 A which is suggestive of a tetrahedral

complex. After heating this complex, its spectrum no

longer exhibits this absorption but rather is similar to

the spectra of the other complexes in the series. During

the determination of the temperature dependence of the

magnetic susceptibility of this complex (Figure 22), it was

observed that the sample began to lose weight at approxi-

mately 660C. This loss in weight is probably due to a

small amount of solvent displaced from the sample. A dif-

ferential thermal analysis on this complex also indicated

an absorption of energy at this temperature. The amount

of solvent present in the complex, however, must be negli-

gible since the analytical results did not indicate any

solvent to be present. This small amount of solvent may

induce some of the molecules to assume a tetrahedral

environment and thereby giving rise to the observed absorp-

tion.










0
0\
C-'
'-4


M M M M M









I- I- 4


E-


I
F-4
H

H




E-4
O
0

oo

4 O
P9 H
< 0









P -

0


o


o\


CMI C

H H 0'-
S1 H CM I
cI c 04 P4 0 A

%-. C v v

c1l 0,4 0 0
'-4 C' Z
0 0 0 0 0
_ 0d 0d L L


0
0
oC
o'









Magnetic measurements

Temperature dependent magnetic susceptibilities

were measured at two different field strengths for each of

the cobalt(II) complexes prepared during the course of this

investigation. The magnetic susceptibilities were corrected

for the diamagnetism of the ligands. These diamagnetic

corrections are listed in Appendix II. The corrected

temperature dependent molar susceptibilities are listed in

Tables 9 through 20. A plot of 1/X vs T for each complex

is presented in Figures 17 through 24. The magnetic moment

of each of the cobalt(II) complexes together with the

appropriate Curie and Weiss constants is listed in Table

21. The slopes of the 1/X, vs T plots were determined

graphically; the Curie constants were obtained by taking

the reciprocal of this slope. The Weiss constants were

determined analytically. Room temperature moments for each

of the nickel(II) complexes were determined at two different

field strengths and are listed in Table 22.

The six-coordinate cobalt(II) complexes (the

perchlorato complex excepted) exhibit normal magnetic

moments (see Introduction). The agreement of the magnetic

moments at the two different field strengths indicates that

the metal ions are magnetically dilute, that is, no metal-

metal interactions exist.










TABLE 9
TEMPERATURE DEPENDENCE OF THE MOLAR SUSCEPTIBILITY
AND MAGNETIC MOMENT OF [CoC12(PAPI)]



T, oK -X x 106(cgs units) Peff(Bohr magnetons)


113.01

122.63

140.64

160.66

178.67

189.37

212.533

295.80

314.17

329.83

348.90

363.97

379.76

397.99


24,894

23,203

20,595

18,124

16,363

15,467
13,822

9,822

9,219

8,783

8,269

7,915

7,570

7,198


4.76

4.79

4.83

4.85

4.85

4.86

4.86

4.84

4.83

4.85

4.82

4.82

4.81

4.81










TABLE 10
TEMPERATURE DEPENDENCE OF THE MOLAR SUSCEPTIBILITY
AND MAGNETIC MOMENT OF [CoBr2(PAPI)]


T, oK Yc x 106(cgs units) eff (Bohr magnetons)

111.50 25,051 4.75
128.37 22,185 4.79
146.31 19,672 4.82
164.25 17,695 4.84
182.19 16,038 4.85
200.06 14,563 4.85
217.93 15,462 4.86
295.72 9,816 4.84
314.81 9,167 4.83

332.75 8,679 4.83
357.75 8,069 4.83
375.45 7,668 4.82
393.68 7,321 4.82
399.93 7,160 4.81










TABLE 11

TEMPERATURE DEPENDENCE OF THE
AND MAGNETIC MOMENT OF


MOLAR SUSCEPTIBILITY
[CoI2(PAPI)]


T, 0K Xc x 106(cgs units) peff(Bohr magnetons)


113.87

128.22

142.58

156.93

171.28

192.81

214.34

290.20

307.28

318.04

335.98

353.93

371.87

389.81

401.72


25,843

21,644

19,679

17,923

16,457

14,634

13,263
9,662

9,124

8,729

8,225

7,842

7,435

7,075
6,852


4.68

4.75

4.76

4.76

4.77

4.81

4.79

4.75

4.75

4.75

4.72

4.73

4.72

4.72

4.71










TABLE 12
TEMPERATURE DEPENDENCE OF THE MOLAR SUSCEPTIBILITY
AND MAGNETIC MOMENT OF [Co(NO2)2(PAPI)]


T, K Xc x 106(cgs units) Peff(Bohr magnetons)

115.37 19,621 4.23
124.99 18,056 4.27
139.35 16,520 4.28
156.57 14,672 4.31
174.51 15,336 4.33
192.45 12,171 4.35
210.40 11,187 4.56
294.65 8,106 4.39
310.15 7,729 4.40
328.59 7,526 4.40
546.17 6,992 4.42
365.55 6,627 4.42
382.99 6,307 4.41
398.92 6,045 4.41











TABLE 13

TEMPERATURE DEPENDENCE OF THE MOLAR SUSCEPTIBILITY
AND MAGNETIC MOMENT OF [Co(NCS)2(PAPI)]


T, OK Xc x 106(cgs units) peff(Bohr magnetons)


112.58

124.28

138.63

152.98

167.34

181.69

196.04

210.40

296.87

510.87

327.01

343.16

561.10

579.04

396.98


22,608

20,620

18,757

17,166

15,750
14,544

13,497

12,651

8,951

8,502

8,101

7,755

7,511

6,953

6,596


4.55

4.55

4.58

4.60

4.61

4.62

4.62

4.65

4.62

4.62

4.62

4.65

4.62

4.61

4.60









TABLE 14
TEMPERATURE DEPENDENCE OF THE MOLAR SUSCEPTIBILITY
AND MAGNETIC MOMENT OF [Co(C10)2(PAPI)]


T, OK )(c x 106(cgs units) eff(Bohr magnetons)

114.23 4,209 1.97
124.28 3,949 1.99

138.63 3,588 2.00
152.98 5,298 2.02
167.34 3,085 2.04
181.69 2,875 2.05
196.04 2,746 2.08
210.40 2,598 2.10
224.75 2,530 2.14
242.69 2,450 2.19
256.47 2,419 2.24
284.10 2,425 2.36
296.51 2,490 2.44

310.87 2,585 2.55
525.22 2,721 2.67
339.57 2,854 2.80
353.93 3,073 2.96
368.28 3,326 3.14
382.63 3,635 3.35
399.14 4,014 3.60










TABLE 15

TEMPERATURE DEPENDENCE OF THE MOLAR SUSCEPTIBILITY
AND MAGNETIC MOMENT OF CoBr2(PAPI)(GREEN)



T, OK (c x 106(cgs units) Peff(Bohr magnetons)


107.48
124.28
158.65
152.98
167.54
181.69
196.04
210.40
293.28
505.69
318.04
352.40
346.75
361.10
375.45
389.81
404.16


20,272
17,911
16,324
14,950
13,845
12,832
11,960
11,228
8,191
7,916
7,611
7,284
7,020
6,756
6,577
6,548
6,196


4.19
4.24
4.27
4.29
4.52
4.34
4.55
4.57
4.40
4.40
4.42
4.42
4.45
4.44
4.46
4.47
4.49









TABLE 16
TEMPERATURE DEPENDENCE OF THE MOLAR SUSCEPTIBILITY
AND MAGNETIC MOMENT OF [CoC12(PAT)2]


T, K Oc x 106(cgs units) Peff(Bohr magnetons)

110.57 22,497 4.48
140.71 18,367 4.57
170.85 15,298 4.59
182.21 14,179 4.56
199.56 13,048 4.58
296.71 8,992 4.64
325.94 8,204 4.64
356.08 7,587 4.67
386.22 6,978 4.66
395.69 6,810 4.66










TABLE 17

TEMPERATURE DEPENDENCE OF THE MOLAR SUSCEPTIBILITY
AND MAGNETIC MOMENT OF [CoBr2(PAT)2]


T, OK Xc x 106(cgs units) Peff(Bohr magnetons)


110.57

124.28

158.65

152.98

167.34

181.69

196.04

210.40

289.19

297.02

310.87

525.22

339.57

353.95

382.65

396.98


21,021

19,038
17,228

15,765
14,529

15,376
12,588

11,615

8,508

8,255

7,887

7,520

7,512
7,085

6,598

6,546


4.55

4.37

4.59

4.41

4.45

4.45

4.42

4.44

4.46

4.44

4.45

4.44

4.48

4.50

4.51

4.51










TABLE 18

TEMPERATURE DEPENDENCE OF THE MOLAR SUSCEPTIBILITY
AND MAGNETIC MOMENT OF [CoI2(PAT)2]


T, oK c x 106(cgs units) peff(Bohr magnetons)

108.49 25,052 4.49
124.28 20,521 4.54
158.65 18,759 4.58
152.98 17,258 4.61
167.534 15,909 4.63
196.04 15,787 4.67
210.40 12,959 4.69
292.06 9,395 4.70

305.69 9,065 4.71
318.04 8,657 4.71
332.40 8,279 4.71
346.75 7,940 4.71
561.10 7,630 4.71
575.45 7,550 4.72
389.81 7,042 4.71
404.16 6,718 4.68









TABLE 19
TEMPERATURE DEPENDENCE OF THE MOLAR SUSCEPTIBILITY
AND MAGNETIC MOMENT OF [Co(NO2)2(PAT)2


T, K X x 106(cgs units) peff(Bohr magnetons)

108.27 21,132 4.30
122.63 18,926 4.33
136.98 17,155 4.35
151.33 15,563 4.36
165.69 14,335 4.38
195.63 12,267 4.40
210.18 11,498 4.42
224.50 10,810 4.42
2963.6 8,246 4.44
326.65 7,522 4.45
356.80 6,893 4.45
386.94 6,285 4.43
400.57 6,086 4.43









TABLE 20
TEMPERATURE DEPENDENCE OF THE MOLAR SUSCEPTIBILITY
AND MAGNETIC MOMENT OF [Co(NCS)2(PAT)2]


T, oK )C x 106(cgs units) peff(Bohr magnetons)

111.36 21,726 4.42
124.28 19,668 4.44
158.63 17,914 4.48
152.98 16,428 4.50
167.54 15,057 4.51
181.69 13,962 4.52
196.04 13,006 4.54
210.40 12,099 4.53
296.51 8,676 4.56

310.87 8,506 4.57
325.22 7,954 4.57
339.55 7,656 4.57
553.95 7,322 4.57
582.65 6,785 4.58
396.98 6,550 4.58























0
0








0





0
-j-










CQ E-i








Ol
0









0
r-


rd o)


0X/T


P-

Z4
H


P-4



0


r4
0
LJ



o

4-'


H


*H P-4

*H- (*'J
,0re
.- 0
4-) 0


C)












P-4



F-40


C0
rrc
Eil(J





H



r=4


0 0 0
LP 0 L'0
Hl H









73








H
P,
-4



0

0

0

ce-3





030


N E-






*4-:
Ep




0


co
C-
(1

(1




o C

-p
H







r4



0P
LC\ 0


0/T





















0
0 _4
4





H
0


00


N 41
4 -P

0
4,


co











C\)





0 4'"
o _











C)
o





C)

0L~- '~


0X/T


0 0 0
Ll 0 Lr0
r-I rH-




































00
CO o
CMJ E-1


0/T


































































0 0
L,- O
r-11-


X/T


















CM

G-41



0
0 CVC

0 0



o


\00
I~c

4-0
\00

4-P



-P


c o 01)
C\J E-1 -
ct)

to
cr)


0CV


rd\



-Py
(13

00
Idr
C)
oo


-ri
CM










0 0 0
LCA 0 L
Hc _


oX/T








78




c'J
C\j


P-f

CCj

0 0 j
-0 0

0
0






co
0










4-,
Cl
$12





0 a
C\j 0
CMU
C~ C\J1
H
00

--.%

4-,





oo

.CM



I 4
0 0 0
LS\0




















1
N
tE-i


0
0




4- '
K\


4-3


C)
CI

co
0











Id
0








0o C)
C'j~ 04
C)












E-4





0
t









'-4q
P-4
CM
9,
bd

r4

0 0 0
L1~\ 0 L


0X/
X/I












TABLE 21

MAGNETIC MOMENTS OF COBALT(II) COMPLEXES AT 2980K AND
CURIE AND WEISS CONSTANTS


Complex


[CoC12 (PAPI)]

[CoBr2(PAPI)]

ICol2 (PAPI)]

[Co (NO2)2 (PAPI)]

[Co(NCS)2(PAPI)]

[Co(C104)2(PAPI)]

CoC12(PAPI) green

CoBr2(PAPI) green

[CoC12(PAT) 2]

[CoBr2(PAT)2]

[Co2 (PAT)2]

[Co (NO2)2 (PAT)2]

[Co(NCS)2(PAT)2]


Peffe

4.84

4.84

4.75

4.39

4.62

2.45

4.54*

4.40

4.64

4.44

4.71

4.44

4.56


Peffb

4.84

4.83

4.75

4.38

4.62

2.45

4.54*

4.39

4.65

4.44

4.71

4.44

4.55


10

4.81

4.81

4.71

4.50

4.63



4.69*

4.56

4.73

4.49

4.81

4.51

4.65


2.87

2.87

2.75

2.51

2.66



2.69*

2.58

2.77

2.50

2.87

2.52

2.68


S(K)

0

0

3

-15

2

Anomalous

-17*

-19

-11

8

-14

-10

-11


aField strength = 6860 Gauss.

Field strength = 5750 Gauss.

*Value reported by Petrofsky (37).

po = 2.84 C1/2.


--























TABLE 22

MAGNETIC MOMENTS OF NICKEL(II) COMPLEXES


Complex Temperature, OK Peffa Peffb

[NiCl2(PAPI)].3/2H20 298.74 3.11 3.11

[NiBr2(PAPI)] 3/2H20 297.52 3.25 3.25

[Nil2(PAPI)] 297.37 3.06 3.06

[Ni(H20) (PA)(PAPI)] 298.74 2.96 2.96


aField strength 6860 Gauss.

bField strength = 5750 Gauss.









As mentioned previously, high-spin cobalt(II) in an

octahedral field has a 4Tlg ground state. This triply

degenerate state provides an orbital angular momentum con-

tribution to the magnetic moment which increases the moment

from 3.87 B.M. (spin-only value) to 4.1 B.M. The still

larger values observed for high-spin octahedral complexes

are explained on the basis of spin-orbit coupling which

mixes in with the ground state some of the higher levels

having orbital angular momentum.

Within a series of similar complexes, two factors

should determine trends in the magnetic moments of these

complexes. One factor is a variation in symmetry caused

by the distortions within the series. The other factor is

the variation in the energy separation between the ground

state and the higher interacting levels. As the energy

separation increases, the degree of mixing decreases.

High-spin complexes with a lower symmetry than Oh

are expected to exhibit magnetic moments which are somewhat

smaller than those with the Oh symmetry because a reduction

in symmetry lifts the degeneracy of the ground state. The

extent of distortion within a complex is expected to de-

termine the degree of quenching of the orbital angular

momentum contribution. On this basis, the observed magnetic

moments were expected to reflect trends which would give

some indication of the distortion within the series of









complexes; however, perusal of Tables 7 and 8 reveals

that no such trend is apparent within the series of com-

plexes investigated.

The isothiocyanato complex is probably the one which

is most nearly octahedral of those within the series be-

cause the effective basicity of this group is closer to

that of PAPI than is the basicity of any other one of the

anions. In spite of this fact, the moments of the iso-

thiocyanato complexes are among the lowest observed. Rather,

a comparison of the A values of these complexes with their

magnetic moments (Table 23) reveals that the energy sepa-

ration between the ground state and the higher interacting

levels is more important in determining the contribution of

orbital angular momentum to the magnetic moment. The level

being mixed in with the ground state is not necessarily

the next higher level. However, this interacting level

does depend inversely on the A values which were obtained

spectroscopically (exceptionCCo(NO2)2(PAPI)]). Therefore,

in conclusion, it may be stated that for the series of

complexes investigated the magnetic moments are more sensi-

tive to ligand field variations than to a reduction of the

symmetry of the ground state.

The temperature dependent susceptibilities of the

above complexes exhibit normal Curie or Curie-Weiss depen-

dence. Within a series of similar complexes (except for















TABLE 23

SUMMARY OF A VALUES AND ROOM TEMPERATURE


MAGNETIC MOMENTS


Complex A, cm-1 Peff

[CoBr2(PAT)2] 12,600 4.44

[Co(N02)2 (PAT)2] 12,900 4.44
[Co(NCS) 2 (PAT)2] 11,800 4.56

[CoCl2 (PAT)2] 11,900 4,64

[Co2 (PAT)2] 10,900 4.71

[Co (NO2)2 (PAPI)] 9,800 4.39

[Co(NCS)2(PAPI)] 12,000 4.62

[Col2(PAPI)] 11,200 4.75
[CoBr2(PAPI)] 10,100 4.84

[CoC12(PAPI)] 9,800 4.84









[Co(NO2)2(PAPI)], the Weiss constants are essentially the
same. The curvature in the plot of 1/c7 vs T for

[CoBr2(PAT)2] (Figure 22) is due to the loss in weight of

the sample at higher temperatures (see Electronic Spectra).

The validity of the prediction of eventual spin-

pairing as a consequence of a tetragonal distortion was

demonstrated with the [Co(C104)2(PAPI)] complex. The room

temperature magnetic moment (2.45 B.M.) could be interpreted

as being characteristic of square planar cobalt(II) com-

plexes (2.1-2.9 B.M.) (15). However, the infrared spectrum

of this complex demonstrates that the perchlorate ions are

indeed coordinated to the metal ion (see Vibrational Spec-

tra). The magnetic susceptibility of a square planar com-

plex would exhibit normal Curie-Weiss behavior; however,

this complex exhibits anomalous behavior (Figure 20). In

light of these observations, it is concluded that the

complex is six-coordinate rather than square planar.

The anomalous behavior can be attributed to an

equilibrium mixture of spin-states. The variation of the

magnetic moment with temperature (Figure 25) is qualita-
tively in accordance with a change in the relative popula-

tions of the high- and low-spin states as described by a

Boltzmann distribution over these states,

Nh/N1 = Ae-E/kT

















0
tU-





"1

.L/
p-


0 0
0 r-
NN\ 0

0
0

0

..p
LO



0
o o


0 *H
0 -P

o
4> 0



















rI
p,
CJ



d



*)

U-P
Fri


quamom OafU SVW]










where Nh and N1 are the populations of the high- and low-

spin states, respectively; AE is the separation between

these two states, and A is a proportionality constant.

The decrease in the magnetic moment with decreasing

temperature depends upon two factors (see Formula): a

lower temperature increases the population of the low-spin

state and a lower temperature also decreases the inter-

nuclear separation between the metal and the ligand which

in turn increases the separation, AE, between the two

states provided the low-spin form is of lower energy.

In view of these observations, it is well established

that a tetragonal distortion does eventually induce spin-

pairing. However, it should be stated that since the

perchlorate ion is such a weak ligand, a very large dis-

tortion is necessary before spin-pairing occurs within the

series of complexes containing PAPI as the in-plane ligand.

By using ligands which produce stronger in-plane ligand

fields, however, such a large distortion may not be neces-

sary. An investigation in this area (together with precise

X-ray measurements) is a necessary extension of this

investigation before subtle variations within a series of

distorted complexes can be explained completely.

The magnetic moments of the two green PAPI complexes

fall within the range characteristic of both octahedral

(4.3-5.2 B.M.) and tetrahedral (4.3-5.1 B.M.) (23) cobalt(II)









complexes. However, principally because of the strong

evidence indicative of tetrahedral complexes exhibited by

the visible spectra (see Electronic Spectra) of these

complexes, it has been concluded that these complexes are

tetrahedral. The magnetic susceptibilities of these two

complexes follow a Curie-Weiss relationship. The lower

magnetic moment exhibited by the bromo complex (Table 21)

appears to be due to a greater loss in symmetry which

splits the higher interacting states which are contributing

orbital angular momentum to the ground state. This vari-

ation in the moment between the two complexes is again an

indication that at least one of the halide ions is co-

ordinated to the metal.

The magnetic moments of each of the nickel(II)

complexes fall in the range expected for high-spin, six-

coordinate complexes. The variation in the magnetic

moments is inversely dependent upon the A values exhibited

by these complexes (the magnetic moment of the chloro

complex being somewhat out of line). This behavior is again

an indication that the energy separation between the ground

state and higher interacting levels is more important in

determining the amount of quenching of orbital angular

momentum than is a slight reduction of the symmetry of the

ground state.









X-ray diffraction patterns

An x-ray diffraction powder pattern of each complex

was obtained in order to further characterize the complexes.

The d-spacings and relative line intensities were determined

and are tabulated in Appendix III.

The diffraction patterns of complexes within a series

are similar; but, it can not be established unequivocally

that the complexes are isomorphous with each other. The

diffraction patterns of both the green CoC12(PAPI) and the

green CoBr2(PAPI) complexes are very distinct from those

of the other PAPI complexes, that is, they exhibit only one

very broad peak. This behavior is indicative of amorphous

solids and it may even suggest polymeric complexes.

This large difference in the x-ray patterns of the

two types of PAPI complexes was a result of a small vari-

ation in their preparations (see Experimental Procedures).

The method of preparation for the octahedral PAPI complexes

is another example of the growing number of template

reactions in which a metal ion serves to promote the syn-

thesis of ligands which are difficult to prepare otherwise.

The change in the diffraction patterns of the un-

heated and heated [CoBr2(PAT)2] complexes demonstrates that

definite rearrangements have occurred in the solid upon

heating the complex above 660C (see Electronic Spectra).












SU "MARY


The synthesis and characterization of sixteen new

complexes of cobalt(II) and nickel(II) are reported. These

complexes are of the type MX2L2 or HX2L' where L refers to

2-pyridinal-p-tolylimine and L' refers to bis(2-pyridinal)-

o-phenylenediimine and X may be C1-, Br-, I-, NO2-, or

C10-. The diffuse reflectance spectrum of each complex was

determined between 3,000 A and 13,500 A. Assignments were

made for some of the transitions and A values were evaluated

from specific absorptions.

The magnetic susceptibilities of the complexes were

determined at room temperature. Twelve of them were

determined as a function of temperature. Eleven of these

complexes exhibit normal Curie-Weiss behavior. One

cobalt(II) complex, the diperchlorato complex, exhibits

anomalous magnetic behavior which is interpreted in terms

of an equilibrium mixture of spin-states (quartet-doublet).

These observations demonstrate that spin-pairing does occur

as a consequence of an axial distortion of a six-coordinate

d ion; moreover, one may infer that a rather large distor-

tion is necessary when the in-plane field is provided by

nitrogen atoms either of the heterocyclic aromatic amine or







91

of the imine type or of both types. Thus, it is concluded

that the equilibrium mixture of spin-states characterizing

a number of six-coordinate cobalt(II) complexes in which

all six coordination positions are occupied by nitrogen

atoms of this type is not attributable to a slight tetra-

gonal distortion.




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