MAGNETIC PROPERTIES OP OXOVANADIUM(IV) COMPLEXES OP

SUBSTITUTED N-(HYDROXYALKYL) SALICYLIDENEIMINES

APPROVEDi

Major Professor

Minor Professor

Direc^^^T^tt^^^e^ment of Chemistry

Carey, E. Franklin, Jr., Magnetic Properties of Oxo-

vanadltim(IV) Complexes of Substituted N-(hydroxyalkyl)

Sallcylldenelmines. Master of Science (Chemistry), May, 1972,

52 pp., 6 tables, 11 illustrations, bibliography, 38 titles.

A series of oxovanadium(IV) complexes of Schiff bases

derived from substituted salicylaldehyde and aminoalcohols

has been prepared and characterized. The Schiff bases coor-

dinate through 0, N, and 0 as tridentate bivalent ligands.

The complexes have the formula V0(X-C^H^(0)CH=:N-(CH2)n0)

where X = H, 5-CI, 5-Br, 5-N02, 3-N02," 5-CH^O, or 3-CH30 and

n = 2 or 3«

The primary purpose of the investigation is to describe

the structure and bonding in these complexes. The subnormal

magnetic properties of the complexes provide much information

about both the structure and the bonding in the complexes.

The magnetic susceptibility of each complex (14 in all)

was measured at five to seven temperatures in the range 78-

300°K. The complexes were also characterized by electron

spin resonance, Infrared, and electronic spectra.

Each complex was found to obey the Bleaney-Bowers

equation for isolated exchange-coupled pairs of S = •§•

vanadlum(IV) ions. The ESR spectra was characteristic of a

molecule involved in singlet-triplet exchange. This evidence

supports a dimeric structure with the two vanadium ions in

the dimer Involved In magnetic exchange.

The magnetic coupling is stronger for the n = 2 com-

plexes than for the n = 3 complexes. This may "be due to the

smaller chelate ring which may cause a stronger overlap of

the vanadium dXy orbitals.

The exchange mechanism for oxovanadium(IV) subnormal

complexes is not known as well as for similar copper complexes.

This study concludes that the exchange mechanism is probably

through a sigma overlap of the vanadium d„w orbitals.

MAGNETIC PROPERTIES OF OXOVANADIUM(IV) COMPLEXES OP

SUBSTITUTED N-(HYDROXYALKYL) SALICYLIDENEIMINES

THESIS

Presented to the Graduate Council of the

North Texas State University in Partial

Fulfillment of the Requirements

For the Degree of

MASTER OF SCIENCE

By

Elbert Franklin Carey, Jr., B. A.

Denton, Texas

May, 1972

ACKNOWLEDGEMENT

The financial support of this investigation by the North

Texas State University Faculty Research Fund and the Robert

A. Welch Foundation is gratefully acknowledged. The elec-

tron spin resonance spectra and the magnetic susceptibility

measurements are due to Dr. Arun Syamal, and his help in the

preparation of this work is also gratefully acknowledged.

ill

TABLE OF CONTENTS

Page

LIST OP TABLES

LIST OP ILLUSTRATIONS vl

Chapter

I. INTRODUCTION 1

II. OXOVANADIUM(IV) COMPLEXES WITH ANTIFERROMAGNETIC EXCHANGE 17 Experimental and Results Discussion

III. CONCLUSION . . . . . . . . . . ^7

BIBLIOGRAPHY 50

iv

LIST OP TABLES

Table Page

I. Analytical Data of Oxovanadium(IV) Schiff Base Complexes . . . * . . 19

II. Magnetic Susceptibility Data for VO(X-Salialcoholamine) Complexes 23

III. Exchange Integral, J, Values for the VO(X-Saljalcoholamine) Complexes 37

IV. Infrared. Absorption Frequencies of V=*0 for the VO(X-Salialcoholamine) Complexes . 41

V. Summary of Assignments for Characteristic Infrared Absorption Bands for the VO(X-Sal«alcoholamine) Complexes . . . . . . . . . . . . . kj

VI. The Electronic Absorption Bands for the VO(X-Salialcoholamine) Complexes . . . . . . . 46

LIST OF ILLUSTRATIONS

Figure Page

1. Singlet-Triplet Splitting in a Dimeric Copper(II) Complex Involved in Magnetic Interaction . . . . . . . . . . . . 6

2. Magnetic Susceptibility of Copper(II) Acetate

Monohydrate as a Function of Temperature. . . 7

3. Sigma Overlap of Two Vanadium d x y Orbitals . . . . 10

Preparation of the X-Salialcoholamine Ligands . . 11

5. Apparatus Used for Measurement of Magnetic

Susceptibility at Low Temperatures. . . . . . 22

6. Infrared Spectrum of VO(Saltpropanolamine) . . . . 27

7. Visible Absorption Spectrum of V0(5-MeO-Sali propanolamine) 31

8. The Three ESR Transitions Expected for a Randomly Oriented Triplet Molecule. . . . . . 32

9. Magnetic Susceptibilities of the V0(X-Saliethanol-amine) Complexes as a Function of Temperature 3^

10. Magnetic Susceptibilities of the V0(X-Salipro-panolamine) Complexes as a Function of Temperature . 35

11. Vanquickenborne-McGlynn Energy Level Diagram for Oxovanadium(IV) 3d Orbitals in Cgv

Symmetry

vi

CHAPTER I

INTRODUCTION

The phenomenon of metal-metal interaction in poly-

nuclear transition metal complexes has become a subject of

great interest in coordination chemistry recently.^" The

interest is directed toward describing the mechanism of this

Interaction* If the metal ions are close enough to allow

overlap of their d orbitals, then the possibility exists for

a direct metal-metal bond. Therefore," it is desirable to

have adequate structural information to postulate this as

the interaction mechanism. Another possible mechanism for

the interaction is through superexchange,^ the involvement

of other atoms, such as the bridging ligands.

Evidence for metal-metal interaction comes primarily

from anomalous magnetic behavior of the complexes. Magnetic

susceptibility is one of the ways in which this behavior can

be studied. A normal metal complex, which involves no inter-

action between the central metal ions, has a magnetic

1G. P. Kokoszka and G. Gordon, "Metal-Metal Exchange Interactions,w in Vol. V of Transition Metal Chemistry (New York, 1969). PP. 181-2777"

2 P. ¥. Anderson, Fhys. Rev.. 79. 350 (1950), 115, 2

(1959).

susceptibility per gram-atom which is given by the following

equation-' 9 «

x , » ! L S « _ (1) A -35$

23 where N Is Avogadro's number » 6.02217 X 10

-21 g is the Bohr magneton = 9*27^10 X 10 erg/G

•"•16

k is Boltzmann's constant = 1.38062 X 10 erg/°K

T is the absolute temperature (°K)

Therefore, the "effective magnetic moment" is

ye a 2.828(XftT)^ Bohr Magnetons (B.M.)

It is necessary to correct the susceptibility for the dia-

magnetism of the ligand and other diamagnetlc groups present.

Thus, the equation is usually in this form

COM1 4 P e a 2.828(Xm T T B.M. (2)

where xjjorr M XA + XL and represents the sum of the

susceptibilities of the diamagnetlc groups or ligands present.

Pascal's constants-^ are used for the estimation of this

diamagnetlc correction.

^A. Eamshaw, Introduction to Magnetochemlstry (London, 1968), pp. 4-6.

The total magnetic moment of a transition metal complex

Is given by the equation**

P S + L = C^S(S+1) + L(L+1)3

where S is the total spin angular momentum, and L la the

total angular momentum of the metal according to the

Russell-Saunders (L-S) coupling scheme.-* It is well-known^

that the experimental values of y are slightly greater than

y_ n = C4S(S+1)3^ which is called the "spin only magnetic o • u •

moment." The orbital angular momentum term is "quenched" by

the ligand field? therefore, Q is usually very close to

the actual magnetic moment of most first row transition metal

complexes.

The magnetic moment (yg) for a single free electron is

given by6

vs = g[s(s+1)]1 (3)

where s is the absolute value of the spin quantum number and

g is the gyromagnetic ratio or the Lande' splitting factor.

For the free electron, g has a value of 2.0023, which may be

taken as 2.00 for most purposes. Therefore, from equation

4 P. A. Cotton and G. Wilkinson, Advanced Inorganic

Chemistry (New York, 1966), p. 636.

"*B. N. Figgis, Introduction to Ligand Fields (New York, 1966), Chapter 10.

^Cotton and Wilkinson, p. 635*

(3)f the spin only magnetic moment for one electron is

u = 2[|?(£+1)3* « 3* - 1.73 B.M. S

This would be the "normal" magnetic moment for a complex

with one unpaired electron.

Magnetic interaction is of two.types, ferromagnetism

and antiferromagnetism. Considering a blnuclear complex

with one unpaired electron on each metal, if the interaction

is ferromagnetic, the ground state energy level corresponds

to parallel spins of the two electrons. In antiferromagnetic

interaction, the reverse is truei the ground state is the

energy level corresponding to antiparallel spins.^ The

latter case, which is much more common, will be of concern

here.

If a complex of a transition metal which has one

+4 unpaired electron in a certain oxidation state (e.g., V, +2

Cu ) has a magnetic moment much less than 1.73 B.M., then

the complex is said to have a "subnormal" magnetic moment.

The best known example of this type of complex is copper(II)

acetate monohydrate, which has a room temperature magnetic 8

moment of 1.40. Copper(II) has the electronic configuration 9

[Ar3 3d and most complexes of it exhibit a temperature

7 B. N. Figgis and J. Lewis, "The Magnetochemistry of

Complex Ions," in Modern Coordination Chemistry (London, I960), pp. 433-^42.

8 B. N. Figgis and B. L. Martin, J. Chem. Soc., 3837

(1956). ~ "

9 Independent magnetic moment In the range 1.75-2,20 B.M.

Bleaney and Bowers10 were the first to explain this anomalous

magnetic behavior of copper acetate. From incomplete

structural data, they postulated a dlmerlc structure with

magnetic Interaction between the electron spins of neigh-

boring Cu(II) ions. This dimeric structure was later confirmed

by X-ray diffraction data.11 This intramolecular antiferro-

magnetic interaction produces a spin singlet state of lower

energy and a thermally populated triplet state some 300 cm 1

above the ground state. They described this interaction with

their susceptibility equation where the symbols have the same

2wfi2 XH S CI + 1/3 exp(^jf)]"1 + Na (4)

meaning as before and Na is the temperature independent

paramagnetism (t.i.p.) and J is the energy separation

between the ground state (spin singlet) and the higher state

(spin triplet), sometimes referred to as the exchange Integral.

This equation is a specific example of Van Vleck's equation

12 for exchange coupled dimers.

^Cotton and Wilkinson, p. 902.

10B. Bleaney and K. D. Bowers, Proc. Boyal Soc. (London), A214, 451 (1952).

11J. N. van Niekerk and F. R. L. Schoening, Acta Cryst., 6, 227 (1953).

12 J. H. Van Vleck, The Theory of Electric and Magnetic

Susceptibilities (London, 1932).

This splitting of the two spin states is shown diagram-

mat ically in Figure 1. The ground state is a spin singlet

(ZS + 1 s 1) corresponding to antiparallel alignment of the

electron spins and consequently diamagnetic. The higher

state is a triplet (2S + 1 • 3) corresponding to parallel

alignment of the electron spins and .consequently paramagnetic.

/

/

/

" x

X

J

\

Triplet (Sail 2S+1=3)

Singlet (S=0 s 2S+l=sl)

Pig. 1—Singlet-Triplet Splitting in a Dlmerlc Copper (II) Complex Involved in Magnetic Interaction.

Since the J value for copper acetate (285 cm"3") Is only

slightly greater than the thermal energy available to it

at room temperature (200 cm"*), the triplet state is

populated and the low magnetic moment results. If the

exchange Integral is much larger than the thermal energy at

room temperature (J»kT), complete diamagnetlsm could result.

As predicted by equation (4), the experimental magnetic

susceptibility of copper acetate is temperature dependent.

8

Magnetic susceptibilities experimentally observed and those

predicted by equation (*0 are plotted versus temperature in

Figure 2. The agreement between experimental and theoretical

results as shown in the graph supports the model of singlet-

triplet splitting.

W •p

(0 bO O

%0 o H

I &

100 200 300

Temperature (°K)

Experimental Values of Susceptibility

Theoretical Values from Equation (*0

Pig. 2—Magnetic Susceptibility of Copper(II) Acetate Monohydrate as a Function of Temperature (from ref. 8).

8

Copper(II) ion and oxovanadium(IV) ion resemble each

other magnetically in that both have one unpaired 3d electron.

The symmetries of the orbitals the electron occupies are,

however, significantly different. In copper(II) complexes

the unpaired electron is in an orbital which is derived from

the eg set of d orbitals in the cubic point group, The

unpaired electron in oxovanadium(IV) complexes is in an or-

bital which is derived from the t£S set of d orbitals in the

cubic point group, Copper(II) complexes with subnormal

magnetic properties are well known,^ but only a few examples

of subnormal oxovanadium(IV) complexes have been reported.16-19

Zelentzov1^ made the first report of such complexes in 1962

when he reported oxovanadium(IV) complexes of substituted N-

(2-hydroxyphenyl) salicylideneimines (I) had magnetic moments

in the range 0.77-1*55 B.M.

^L. S. Porster and C. J. Ballhausen, Acta Chem. Scan., 16, 1385 (1962).

i it C. J. Ballhausen and H. B. Gray, Inorg. Chem.. 1,

111 (1962).

^ M . Kato, H. B. Jonassen, and J. C. Panning, Chem. Revs.. 64;, 99 (1964).

16 V. V. Zelentsov, Russ. J. Inorg. Chem.. £, 670 (1962).

^A. P. Ginsberg, E. Koubek, and H. J. Williams, Inorg. Chem., 1656 (1966).

18 C. C. Lee, A* Syamal, and L. J. Theriot, Inorg. Chem..

10, 1669 (1971).

^Y. Kuge and S. Yamada, Bull. Chem. Soc. of Japan. 43. 3972 (1971).

He suggested a dimeric structure (II) similar to copper(II)

complexes with antlferromagnetic exchange was also probable

In the case of the oxovanadium(IV) complexes.

Mr

H26 ~

II

This dimeric structure was later supported by Ginsberg and

coworkers"1"^ who studied the temperature dependence of the

susceptibility of the complexes and found that they obeyed

the Bleaney-Bowers equation (4) for isolated exchange coupled

pairs.

Since the symmetry of the orbital occupied by the

+2 +2

unpaired electron in Cu and VO complexes is so different,

the question arises whether the mechanism for magnetic inter-

action is the same for both. The unpaired electron in copper

(II) complexes is In the d 2 2 orbital.^ The oxygen-x

bridged structure (III) for a copper complex has been verified

by an X-ray diffraction structure determination.

10

20

III

Considering the dx2_y2 orbital on each copper In III Is

directed toward the llgand donor atoms, the principal path

for spin interaction between the two copper Ions should be 2

through the two bridging oxygens* that is, superexchange,

In oxovanadium(IV) complexes, however, the unpaired lij,

electron is in the dxy orbital. Considering the dxy

orbital on each vanadium In II, they have the correct symmetry

for a direct sigma overlap as shown in Figure 3.

i o ^ < n > Y < o

Fig. 3—Sigma Overlap of Two Vanadium dxy Orbitals

One factor which limits the interpretation of oxo-

vanadlum(IV) magnetically anomalous systems is the absence

20 G. A. Barclay and B. P. Hosklns, J. Chem. Soc.. 1979

(1965). ~

11

of complete structural information. There has never been an

X-ray structural determination on a complex of the type II

because all complexes reported so far have been non-

crystalline. They are frequently insoluble powderst this

prevents other structural studies such as molecular weight

measurements. Synthesis of new complexes in this series is

always undertaken in the hope that suitable crystallinity

can be obtained for an X-ray structure determination.

In an effort to continue the investigation of the inter-

action in dimerlc oxovanadium(IV) complexes, a series of

complexes with substituted N-(hydroxyalkyl) salicylideneimines

has been prepared. The ligands are Schlff bases derived from

substituted salicylaldehyde and aminoalcohols. The preparation

of the ligands, abbreviated (X-Saljalcoholamine), is shown in

Figure The ligands are bivalent anions with tridentate

0N0 donor atoms.

'1 • •w»°' =*

X-Salicylaldehyde Alcoholamine X-Salialcoholamine

Pig. 4—Preparation of the X-Salialcoholamine ligands

12

They form complexes with V0+2 which are believed to be of

th« type IV similar to the other reported oxovamdium(IV)

16-19 complexes with subnormal magnetic properties.

b 3

=r-(CH2)n

Yamada and Kuge*^ recently reported three complexes of

this series (X=H, n=2; X=H, n=3? X=3-Me0, n=3) and found

room-temperature magnetic moments which are subnormal, but

differ somewhat from the values reported here. Poddar and

21

coworkers synthesized what they formulated as VO(OH)

(Saliethanolamine-H), where the alcohol hydrogen is not lost

and the ligand is monovalent. They reported a room-temp-

erature magnetic moment which agrees with the value reported

here and not with Yamada and Kuge's value. Poddar et al.

suggested the structure (Va or Vb), which is in disagreement

with other suggested structures y of dimeric oxovanadium

(IV) complexes.

21S. N. Poddar, K. Dey, J. Haldar, and S. C. Nathsarkar, J. Indian Chem. Soc., 7^3 (1970).

13

OH

Va Vb

In order to provide more information on the structural and

magnetic properties of oxovanadium(IV) complexes with these

ligands, this investigation was undertaken.

The copper(II) complexes of substituted N-(hydroxy-

alkyl) salicylideneimlnes and related ligands have been

22*a>26

studied by several investigators, "* In most cases

these complexes have subnormal magnetic properties? however,

some interesting structural differences have been found

between the complexes of the ligands derived from ethanol-

amine and those derived from propanolamine. Bertrand and 22 S. Yamada, Y. Kuge, and K. Yamanouchi, Inorg. Chlm,

Acta, 1, 139 (1967). 23 M. Kato, Y. Muto, H. B. Jonassen, K. Imai, and

A. Harano, Bull. Chem. Soc. of Japan. 41. 1864 (1968). Oil J. A. Bertrand and J. A. Kelley, Inorg. Chlm. Acta,

4, 203 (1970).

2^J. A. Bertrand, J. A. Kelley, and J. L. Breece, Inorg. Chlm. Acta, 4, 247 (1970).

26 A. Nakahara, H. Yamamoto, and H. Matsumoto, Chem.

Abstr.. 62, 215e (1965).

14

2 LL

Kelley studied the structure of Via and VIb by X-ray

diffraction. For Via, they found a tetrameric complex

CH3 c h 3 \

H-CS^C ° \ u H-C^ °\:tL

CH f NcH2)2 C K f ^ V(CH 2 >3

Via VIb

with a normal magnetic moment (ye « 1.87). They described

the structure as two dimers held together by Cu-0 bonds,

where the coordination about oxygen is tetrahedral (sp^).

For VIb, they found a dimeric complex with a subnormal

magnetic moment (ye = 0.41). The coordination about oxygen

? is planar (sp ). They suggested the principal difference

in the two was the hybridization of oxygen. In VIb the

2 planar sp oxygen has a free p orbital available for pi

•>

bonding* whereas in Via the tetrahedral sp-' oxygen has no

free p orbital and could not form a pi bond. They showed^-*

that the difference in the coordination about copper was

not responsible for the difference in magnetic properties

by solving the structure of VII. They found the coordination

about copper was similar to Via and the coordination about

oxygen was similar to VIb, Since VII has a subnormal mag-

netic moment (1.10 B.M.), it is>therefore involved in

\

15

VII

magnetic exchange. The principal pathway for this exchange

2

must be through the bridging oxygens, which are sp hybridized

and have an available p orbital for pi bonding. This work

was undertaken to see if this difference in structure and

magnetic properties could be seen in analogous oxovanadium

(IV) complexes.

Ginsberg et al.1"^ found that the exchange integrals (J)

for his oxovanadium(IV) subnormal complexes showed a quite

different dependence on the substituents on the benzene ring

than did the analogous copper complexes. Although temperature

studies of the susceptibility dependence of the analogous

copper complexes have yet to be done, another aim of this

study is to compare the exchange integrals for the oxovanadium

(IV) complexes with those of the copper complexes.

Thus, this work was undertaken for the following reasonsi

(1) in hope of obtaining crystalline complexes suitable for

X-ray structure determination, (2) to resolve the disagree-

ment over the structure and magnetic properties of the com-

plexes already reported, (3) to see if the role of the +2

bridging group in the VO complexes was similar to that in

+2 the Cu complexes, (^) to see the effect of the substituents

16

on the magnitude of the exchange integrals, and (5) ulti-

mately, to compare the magnitude of the exchange integrals

+2 +2 of the VO complexes with those of the Cu complexes, and

perhaps demonstrate the difference in the interaction

mechanisms.

CHAPTER II

0X0VANADIUM(IV) COMPLEXES WITH ANTIFERROMAGNETIC EXCHANGE

Experimental and Results

Reagents

Reagent grade salicylaldehyde and sodium acetate were

obtained from J. T. Baker Chemical Co,, Phillipsburg, New

Jersey. Vanadyl dichlorlde was obtained from K & K Labora-

tories, Plainview, New Jersey. 5-Chlorosalicylaldehyde,

5-bromosalicylaldehyde, 3-nitrosalicylaldehyde, 5-nltro-

salicylaldehyde, and 3-amlno-l-propanol were obtained from

Eastman Organic Chemicals, Rochester, New York. 3-Methoxy-

salicylaldehyde and 5-methoxysalicylaldehyde were obtained

from Aldrich Chemical Co., Milwaukee, Wisconsin. Ethanol-

amlne was obtained from Matheson Coleman & Bell, Norwood,

Ohio. Ethanol was obtained from U. S. Industrial Chemical

Co., New York, N. Y. All other chemicals used were of re-

agent grade quality.

Preparation of the Complexes

The VO(X-Salialcoholamine) complexes were prepared by

the following general method. Vanadyl dichlorlde (0.025

mole) was dissolved in 30 ml of absolute ethanol. Anhydrous

sodium acetate (0.05 mole) was added and the mixture was

stirred a few minutes and then filtered. Separately,

17

18

X-salicylaldehyde (0.025 mole) and the appropriate amino-

alcohol (0.025 mole) were mixed in 100 ml of absolute ethanol

and refluxed for 30 minutes. The resulting yellow solution

of the Schiff base was added slowly to the magnetically

stirred filtrate from above, containing vanadyl acetate.

This mixture was then refluxed for three hours while stir-

ring. The precipitate was collected on a filter, washed

several times with absolute ethanol, and then dried for

several hours in a vacuum desiccator at 30°C. The yield

is about 65% based on vanadyl dichloride. The complexes are

usually brown or green powders which are insoluble in all

common solvents. The melting points of all the complexes in

sealed tubes are all greater than 250°C.

Analyses of the Complexes

Carbon, hydrogen, and nitrogen analyses were performed

by Galbraith Laboratories, Knoxville, Tennessee and by

C. P. Geiger, Ontario, California. The analytical results

are listed in Table I.

Electron Spin Resonance Spectra

Electron spin resonance (ESR) spectra of three of the

complexes were obtained (by A. Syamal) on a Varian model

V^502 ESR Spectrometer. The spectra were obtained on powdered

samples in a quartz tube because the complexes are insoluble

in common solvents. A minute sample of finely powdered di-

phenylpicrylhydrazyl (DPPH) was used as a reference, or

19

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VO co VO CO <w

o P O O ?> > > >

20

g-marker. The g values for the complexes were calculated by

measuring the field separation "between the center of the spec-

trum and the signal of the reference. This distance, gH, is

1 then used to calculate the g value of the sample by the equation

g = 2.0036 (1 - (5)

where 2.0036 is the g value for DPPH and H is the magnetic

field strength which is known approximately from the reso-

nance frequency. The g value obtained for all three complexes

by this method was 2.00.

Magnetic Susceptibilities

The magnetic susceptibilities of all the complexes were

obtained (by A. Syamal) at five to seven temperatures in the

range 78-297°K by the Gouy method.2 Liquid nitrogen (?8°K)

and room temperature (293-297°K) measurements were obtained in

the usual manner.2 The measurements in the range 128-265°K

were obtained by the following method. The sample tube was

placed in a cylindrical copper tube which was surrounded by

a glass jacket. Nitrogen gas, cooled in a reservoir of

liquid nitrogen, was passed around the copper tube through

the jacket. Various temperatures were obtained by regulating

the rate of flow of the nitrogen gas into the liquid nitrogen

reservoir. The temperature was measured by a copper-constantan

^P. B. Ayscough, Electron Spin Resonance In Chemistry (London, 1967), p. 156.

2 Earnshaw, Introduction to MaKnetochemlstrv. pp. 8^-9^.

21

thermocouple placed near the sample and connected to a Leeds

and Northrup model 8691 millivolt potentiometer with an ice-

water bath as the reference temperature. The temperature of

the ice-water reference was checked periodically. All

measurements were made in an atmosphere of Argon to prevent

frost formation. The apparatus is shown in Figure 5-

An Alpha model 7500 electromagnet equipped with a power

supply and current regulator was used for the measurements.

The susceptibilities shown in Table II are the averages of

values at three different fields (at each temperature)

roughly corresponding to 6000, 7000, and 8000 gauss. Mercury

tetrathiocyanatocobalt(II) was used as the calibration stan-3

dard. The accuracy and precision of the apparatus were found

to be within acceptable limits by measurements of the suscep-it

tibilities of copper sulfate pentahydrate and copper acetate

monohydrate.^ The susceptibilities were corrected for t.i.p.

-6 n

(Na), using a value of 50 X 10 units of susceptibility. The

magnetic moments shown in Table II were then calculated from

equation (2).

Infrared Spectra

The infrared (IE) spectra of all the complexes were

obtained from 4000 cm"^ to 300 cm"* " on a Perkin Elmer model

621 Recording Spectrophotometer. Nuj.ol mulls on cesium

^B. N. Figgis and R. S. Nyholm, J. Chem. Soc., 4190 (1958) it Figgis and Nyholm, J. Chem. Soc., 331 (1959)*

^Figgis and S. L. Martin, J. Chem. Soc.. 3837 (1956).

Argon Gas Outlet

Argon Gas Inlet

22

Copper Chamber

Nitrogen Gas Inlet

Glass Jacket

•Nitrogen Gas Outlet

Ice-water Ice-water Reference

Potentiometer

thermocouple

Liquid Nitrogen Reservoir

Fig. 5—Apparatus Used for Measurement of Magnetic Susceptibilities at Low Temperatures.

23

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26

iodide salt plates, which had been previously polished with

a $0% ethanol-water mixture, were used for all the complexes.

The nujol used was commercial grade and showed no water bands.

Potassium bromide disks were also used for several of the

complexes. The KBr pellets were made with a Wilks Scientific

mini-press using infrared spectroscopy grade potassium bro-

mide. They were dried in a vacuum desiccator at 150° for

three hours before recording the spectrum. The IR spectrum

of VO(Salipropanolamine) is shown in Figure 6. The spectra

of the other complexes are very similar and show no water

bands.

Electronic Spectra

The electronic spectra of all the complexes were ob-

tained in the region 6,667 cnf^dSOO nm) to 33»300 cm'^OOO

nm) on a Cary model 14 Recording Spectrophotometer. Because

of the extreme insolubility of the complexes, the spectra

were obtained by mulling the complexes in nujol as described

in the literature.^ The absorption spectrum of V0(5-Me0-

Salipropanolamine) is shown in Figure 7. The spectra of the

other complexes are similar, but not all have as well-defined

bands.

6 F. A. Cotton, J. Am. Chem. Soc.. 83, 4157 (1961).

27

80%

3400 3200 3000

(Frequency, cm""'1')

Fig. 6—Infrared Spectrum of VO(Saljpropanolamine)

2800

28

8056

60$

40$

20$

2600 2400 2200

(F requency , cm""*1')

P i g . 6 ( c o n t i n u e d )

2000

29

80%

60%

40$

20$

V C=N

A

C-N

1800 1600 1^00

(Frequency, cm""1)

Fig. 6 (continued.)

1200

30

-80»

-60/5

-AO

— 2 •)%

C - 0

v=o

n

v

1000 800

( F r e q u e n c y , cm-"'")

600 400

P i g . 6 ( c o n t i n u e d )

31

A ft

Mi 810 ~ — -

-----

— - -

A ft

Mi 810 772 ~ — -

-----

— - -

A ft

Mi 810 772 ~ — - — - -

A ft

Mi 810 —

.

A ft

810 —

t •*

.

- — ~

0.8 -JV

u req u en t cur L)

- — -

- — ~

0.8 -JV — _ .

- — -

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- — ~ —

-JV

_ - — ~ _ —

-— _ — — _

r 7 - — — —

— r 7 - — — —

— — -r 7

A *t

—

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0.7 0.7 — ~

_ _

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j — _ _

0.7

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—

—

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—

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U.O

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A— - — -

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—

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— U*o

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— —

-A Q-U • o

V V -J— -J— -A O-U.<£

-0.1

420 460 500 5^0 580 620 660 700

(Wavelength, nm)

Fig. 7—Visible Absorption Spectrum of V0(5-MeO-Sali propanolamine),

32

Discussion

Electron Spin Resonance Spectra

The Investigation of the ESR spectra of the oxovanadium

(IV) complexes was undertaken mainly for the purpose of cal-

culating g values for use in equation (4). The procedure

used for this purpose has been described earlier.

However, the spectra obtained for these complexes

deserves some consideration. For a randomly oriented mole-

cule in the triplet state with zero-field splitting, three

7

transitions are expected, corresponding to AMg = 2, 1, and

1. The energy level diagram shown in Figure 8 shows the

effect of the increasing magnetic field on the energy of the

spin states and the three transitions.

AM0=I AMS=2

AMossl

H

Fig. 8—The Three ESR Transitions Expected for a Randomly Oriented Triplet Molecule (from ref. 7)«

E. Wasserman, L. C. Snyder, and W. A. Yager, J. Chem. Phys., 41, 1763 (1964).

33

The two transitions corresponding to AMS = 1 are ob-

served in these complexes in the region 2000-4800 gauss and

are complicated by anisotropy, The AMS = 2 transition, or

"half-field transition," is observed for these complexes in

the region of 1?00 gauss. The observation of this transition

provides convincing evidence for a singlet-triplet dimeric

complex, since this transition would not occur for a mono-

8

merle spin doublet complex. Belford et al. have observed

this transition in solution spectra of binuclear oxovanadium

(IV) complexes and it has also been observed in other powdered 9

samples of oxovanadium(IV) dimers.

Magnetic Susceptibilities

The magnetic susceptibilities of the VO(X-Sal»alcohol-

amine) complexes separate the complexes into two groups.

The VO(X-Saliethanolamine) complexes (n = 2 In IV) have, in

general, lower susceptibilities than the VO(X-Sal»propanol-

amine) complexes (n s 3 in IV). The magnetic susceptibility

of each complex is plotted as a function of temperature for

these two groups in Figures 9 and 10.

The dependence of the susceptibility on temperature for

both series of complexes is characteristic of antiferromagnetic

8 R. L. Belford, N. D. Chasteen, H. Su, and R. E. Tapcott,

J. Am. Chem. Soc., £L, 4675 (1969). o A. Syamal and L. J. Theriot, to be published.

3^

W -P •H a 2

CO fco • o

vo o

SJ

«P

•P P. 0) O CO 3 CO o •H 4> 0)

<« £3

800

600 ~

^00 -

200 ~

300

Temperature ( K)

Fig. 9—Magnetic Susceptibilities of the VO(X-Saliethanol« amine) Complexes as a Function of Temperature.

35

W 4->

CO W m

o vo

1600 -

o H

8

s X

«p •H iH •H ,0 •H •P Pi <D O w 2 CO

•p <L> £ ao S3

1200

800 -

**00

X=5-MeO

100 150 200

Temperature (°K) 300

Pig. l6—Magnetic Susceptibilities of the V0(X-Sal: propanolamine) Complexes as a Function of Temperature.

36

interaction.10 The characteristic temperature of antiferro-

magnetism, below which the susceptibility drops with decreas-

ing temperature, is called the Neel temperature. For most of

the VO(X-Saliethanolamine) complexes (X = H is an exception),

the Ne'el temperature appears to be greater than room tempera-

ture. However, for most of the VO(X-Salipropanolamine) com-

plexes (X ss 5-N02 is an exception), the Ne'el temperature is

less than room temperature.

The exchange integral, J, was evaluated for each complex

by substituting the susceptibility data of Table II into

equation (4). A g value of 2.00 and a value of 50 X 10~^

c.g.s. units of susceptibility for Na were used. The results

are shown in Table III. Once again, the two groups of com-

plexes (n ss 2 and n = 3) show differences in both magnitude

of the J values as well as a different dependence on the

substituent group, X.

The dependence of the J values on n is quite marked.

The J values for the n = 2 complexes are higher than the J

values for the n = 3 complexes. This means the antiferro-

magnetic exchange coupling is stronger for the V0(X-Sali

ethanolamine) complexes than the VO(X-Salipropanolamine)

complexes. This difference may be due to the size of the

chelate ring. If the alcohol portion of the ligand is the

10Cotton and Wilkinson, Advanced Inorganic Chemistry, pp. 642-3. "

37

TABLE III

EXCHANGE INTEGRAL, J, VALUES FOR THE VO(X-Salialcoholamine) COMPLEXES

Complex Exchange Integral, J* (cm-1)

VO(Sal«ethanolamine) . . . . 221

VO(5-Cl-Saliethanolamine). . . . . . 33^

VO(5-Br-Sal»ethanolamine). . . . . 328

VO(5-N02~Saliethanolamine) 3^3

V0(3-N02~Saljethanolamine) . . . . . . . . . . ^89

VO{5-MeO-Saltethanolamine) 399

VO(3-MeO-Sal»ethanolamine) . . . 520

VO(Sals propanolamine)............ . 144

VO(5-Cl-Sal»propanolamine) 156

VO(5-Br-Saltpropanolamine) . 168

VO (5-N02"Sal t propanolamine) 298

VO(3-N02~Sal:propanolamine). 150

VO( 5-MeO-Salx propanolamine) 120

VO (3-MeO-Sal 1 propanolamine). . 1*14

•Calculated from Equation (4-), g s 2.00, Na a 50 X 10~ c.g.s. units.

38

bridging group, as is the case in the analogous copper com-

plexes,1"1 then the interaction would be expected to be greater

for the n = 2 complexes than the n = 3 complexes.

The two structures are shown below. The five-membered

Villa

2 £ i h 2

VII lb

chelate ring (Villa) would have a narrower O-V-N bond angle

than the six-membered chelate ring (Vlllb). The smaller

chelate ring would cause the V-O-V angle in Villa to be nar-

rower than Vlllb. Thus, the two vanadiums would be closer

together in Villa than Vlllb. One would expect the magnetic

interaction to be stronger in Villa than in Vlllb and this

has been shown to be the case.

In the absence of definite structural data, very little

can be said about the dependence of the J values on the sub-

stituent group, X. For the VO(X-Sal«ethanolamine) complexes,

the ligands substituted in the 3~position have larger J values

than the complexes of the ligands substituted in the 5-position.

11 M. Kato, Y. Muto, H. B. Jonassen, K. Imai, and A. Harano,

Bull. Chem. Soc. of Japan, b1, 1864- (1968).

39

For the VO(X-Sal:propanolamine) complexes, the electronic

effect of the substituent seems to play a more important

role. V0(5-N02-Salipropanolamine) has a much larger J value

than any other complex in its series. V0(5-Me0-Salipropanol-

amine) has a smaller J value than any other complex in the

series. The nitro group is electron-withdrawing and. the

methoxy group is electron-donating. This difference in

dependence of the J values on the substituent group in the

two series might be interpreted in terms of the interaction

mechanism. One could argue that it is different for the two

series of complexes.

Infrared Spectra

The infrared spectra of the VO(X-Salsalcoholamine) com-

plexes are very similar except for absorption bands which

may be attributed to the different substituents on the aro-

matic ring. The infrared spectrum of VO(Salspropanolamine)

shown in Figure 6 will be used for the basis of discussion.

The same general assignments will hold for all the complexes.

The absence of a band in the 3000 cm"1 to 3500 cm"1

region indicates the absence of water in the complexes,

either coordinated or as water of hydration. This is confirmed

by the analytical data. The strong absorption band at 1605

cm"1 in VO(Salipropanolamine) is assigned to the C=N stretch-

ing vibration.12 The three bands in the region 1440 cm"1 to

12 P. Teyssie and J. Charette, Spectrochim. Acta, 19, 1407

(1963).

40

1540 cm can be assigned to the benzene ring stretching

vibrations. The weaker bands in the region 1000 cm"1 to

1400 cm can also be assigned to the benzene ring and its

substituents.1^ The stronger bands at 1310 cm-"'" and 1060 -1

cm can be assigned to the C-N and C-0 stretching vibrations,

respectively.1-*

The strong band at 970 cm"1 is due to the V=0 stretch-

ing vibration.16 This is a very important diagnostic band

in all oxovanadium(IV) complexes and the absorption frequency

for each of the complexes is shown in Table IV. The bands

are usually very strong and broad and are found in the region

880 cm"1 to 998 cm"1 for the V0(X-Sal,aIcoholamine) complexes.

As pointed out by Ginsberg et al.,1? two V=0 stretching fre-

quencies can be observed for this type of compex due to unit

cell group splitting or to a crystal packing effect. The

bands for the VO(X-Salsalcoholamine) complexes are very broad

and are sometimes observed as doublets separated by 20 cm"1

or less.

cules^(London?^1958) § 7 Mole-

14 Bellamy, pp. 81-83.

15 T-, .,5? M. Silvestein and G. C. Bassler, Spectrometric Identification of Organic Compounds (New York, 1967),"Chap-

Nucl^ciem?.b2": 1359' (flalf: S - P - M o G l y n n - £• IS2Eg.

,E" KOUbek• and H" J> Wllllams'

in

TABLE IV

INFRARED ABSORPTION FREQUENCIES OF V=0 FOR THE VO(X-Saljalcoholamine) COMPLEXES

Complex Frequency (cm"-'-)

VO(Sal«ethanolamine) 971

VO( 5-Cl-Sals ethanolamine) 995

VO(5-Br-Sal:ethanolamine). 987

V0(5-N02~Sal1ethanolamine) . . . . . . . . 916

V0(3-N02*-Sal: ethanolamine) 995

VO(5-MeO-Saliethanolamine) , 998

V0(3-Me0-Sal»ethanolamine) . . . . . 976, 995

VO(Salspropanolamine) 970

V0(5-Cl-Salrpropanolamine) 980

VO(5-Br-Sal:propanolamine) . . . . . . . . . . . . . 968

VO (5-N02~Sal < propanolamine) 880

V0(3-N02*-Salspropanolamine). 963

VO (5-Me0-Sal j propanolamine) 963

VO (3-Me0-Sal t propanolamine) 97/*, 986

42

The bands in the region 700 cm""*" to 900 cm"*"*" are attri-

buted to the out-of-plane C-H deformation vibrations on the

18

benzene ring. The bands indicate the substitution pattern

of the ring. The strong absorption at 768 cm""1" in V0(Sal»

propanolamlne) indicates a 1,2-disubstltuted benzene ring.

The bands in the 500 cm"""'* to 700 cm"'"1' region are attributed

to metal-chelate ring vibrations. A summary of the assign-

ments for the characteristic absorption bands for the V0(X-

Salsalcoholamlne) complexes is given in Table V. 18 Bellamy, pp. 75-81

4 3

S !

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FL O •H 43 A$ u P

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O •P 0 F-T -P CO

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O O O~

CO a o •H 43 AS J3

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a

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A A P

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Electronic Spectra

Several energy level diagrams have been proposed for

oxovanadium(IV) complexes.^-9-21 m oi e c ui a r orbital dia-

gram for V0(H20)1j2 (in symmetry) derived by Ballhausen

19 21 and Gray has been revised by Vanquickenborne and McGlynn.

The energy level diagram shown in Figure 11 is due to Van-

quickenborne and McGlynn and is reasonable for the VO(X-Sal»

alcoholamine) complexes.

dz2

E

dx2_y2

yZ Lxz

Lxy

Pig, 11—Vanqulckenborne-McGlynn Energy Level Diagram for Oxovanadium(IV) 3d Orbitals in C 2 v Symmetry.

19 C. J. Ballhausen and H. B. Gray, Inorg. Chem., 1, 111

(1962). ~ 20 J. Selbin, G. Maus, and D. L. Johnson, J. Inorg. Nucl.

Chem., 2£, 1735 (196?). 21 L. G. Vanquickenborne and S. P. McGlynn, Theor. Chlm.

Acta. % 390 (1968).

^5

As pointed out by Vanquickenborne and McGlynn, the

reduction of symmetry from the C^v used by Ballhausen and

Gray to C 2 v results in the splitting of the d y z and d x z orbi-

tals. The VO(X-Saljalcoholamine) complexes show this effect

quite clearly. A broad adsorption band for all the complexes

is observed in the region 12,500 cm-1 to 18,000 cm"*1. In

most cases this band consists of two shoulders. The low-

energy maximum is centered roughly around 13,500 cm"1 and

the high energy maximum is around 16,500 cm"1. This band is

assigned to the d x y d x z and d x y dyZ transitions, respec-

tively. As they are labeled in Table VI, band la is the

d x y -*• d x z transition and band lb is the d x y •* d y z transition.

The second band is observed in the 18,300 cm"1 to 20,300

-1

cm region. This band is usually well-developed, although

sometimes it is observed as a shoulder of band III. Band II

is assigned to the d ^ dx2_y2 transition.

The third band is centered in the 2^,^00 cm"1 to 27,^00

cm"1 region. This band is more intense than bands I and II

and is believed not to be a d-d transition. It has been

shown^ that a Zn(ONO) complex has a similar band. Since

Zn(II) is a d1® system, no d-d bands are expected for this

complex. Thus, band III is believed to be a charge transfer

band. The fourth d-d transition, d x y dz2, expected for

oxovandium(IV) complexes is believed to be buried beneath

this band.

22L. J. Theriot, G. 0. Carlisle, and. H. J. Hu, J. Inorg. Nucl. Chem.. 31, 284l (1969).

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CHAPTER III

CONCLUSION

Extensive magnetic and spectral studies on the struc-

ture and bonding of the oxovanadium(IV) complexes of substi-

tuted N-(hydroxyalkyl) salicylideneimines have been done.

The fact that the complexes obey the Bleaney-Bowers equation

for isolated exchange coupled pairs and the observation of

the half-field transition in the ESR spectra is strong evi-

dence that the complexes are dimeric as shown in IV. Since

the complexes are amorphous solids which are insoluble,

structural studies such as X-ray crystallography or molecular

weight measurements cannot be done. Thus, all structural in-

formation which can be obtained from magnetic data is very

important.

In contrast to the situation with copper(II) subnormal

complexes, where extensive studies have been done, very

little work has been done with oxovanadium(IV) subnormal com-

plexes. The superexchange mechanism for copper subnormal

complexes is fairly well established and accepted. The inter-

action mechanism in oxovanadium(IV) subnormal complexes is

believed to be through a direct metal-metal bond formed by

overlap of the vanadium dyy. orbitals in the dimer. Therefore,

It is necessary to have more examples of oxovanadium(IV) sub-

normal complexes and as much structural information as possible

4?

48

before the metal-metal bond mechanism can become as well-

established as the superexchange mechanism is for copper.

There has been some disagreement in the literature over

the structure and magnetic properties of the oxovanadium(IV)

1 2 complexes of substituted N-(hydroxyalkyl) salicylideneimines. '

o

Kuge and Yamada reported the X=H, n=2; the X=H, n=3» and the

Xs3-Me0, n=3 complexes (in IV) had room-temperature magnetic

moments of 1.06 B.M., 1.36 B.M. , and 0.87 B.M., respectively.

The values reported here for the same three complexes are

1.41 B.M. t 1.53 B.M. , and 1.54 B.M. Poddar et al.1 reported

a room-temperature moment of 1,42 B.M. for their oxovanadium

(IV) complex of Sal:ethanolamine. However, they formulated

the complex as VO(OH)(C6H^(0)CH=N(CH2)20H) with the structure

shown previously (V). The color and solubility of the complex

reported by Poddar et al. is very similar to those of the

V0(Saliethanolamine) complex reported here.

The structure proposed by Poddar et al. for their com-

plex V0(C5H^(0)CH=N(CH2)20H) does not agree with the experi-

mental data reported here for VO(Saliethanolamine). This

polymeric distorted octahedral structure (V) may be ruled out

for the complexes reported here for the following reasons;

(1) elemental analyses do not agree with this formulation,

1S. N. Poddar, K. Dey, J. Haider and S. C. Nathsarkar, J. Indian Chem. Soc., 4£, 743 (1970).

2 Y. Kuge and S. Yamada, Bull. Chem. Soc. of Japan. 43.

3972 (1971). —

^9

(2) there is no 0-H stretching vibration in the infrared.

spectra, and (3) the magnetic susceptibility data and ESR

spectra support a dimeric structure as discussed earlier.

The role of the bridging group in the oxovanadium(IV)

complexes is not the same as it is in analogous copper(II)

complexes. The copper(II) complex of the Schiff base derived

from acetylacetone and ethanolamine is tetrameric and has a

"normal" magnetic moment of I.87. Recent worlP indicates

that this may be due to ferromagnetic interaction. The copper

(II) complexes with tridentate Schiff bases with 0N0 donors

derived from propanolamine have magnetic moments in the range

0.4- - 0.5. The oxovanadium(IV) complexes with tridentate

Schiff bases with 0N0 donors derived from ethanolamine and

propanolamine are both involved in antiferromagnetic exchange.

The exchange coupling is stronger for the complexes of Schiff

bases derived from ethanolamine. This difference in magnetic

properties may indicate a difference in the interaction

mechanism between copper and vanadium. In the copper complexes,

the exchange coupling is believed to take place by superex-

change through the bridging oxygens. In the oxovanadium(IV)

complexes the exchange coupling may take place through a

direct sigma overlap of the vanadium dx;y orbitals, as shown in

Figure 3.

3 A. Syamal and L. J. Theriot, to be published.

BIBLIOGRAPHY

Books

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Bellamy, L. J., The Infrared Spectra of Complex Molecules, London, Methuen & Co., Ltd., 195*87

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Earnshaw, A., Introduction to Magnetochemistry, London, Academic Press, Inc. 7 196"BV

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Van Vleck, J. H., The Theory of Electric and Magnetic Susceptibilities, London, Oxford University Press, 1959.

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50

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Lee, C. C., A. Syamal, and L. J. Theriot, Inorganic Chemistry, 10, 1669 (1971).

Nakahara, A., H. Yamamoto, and H. Matsumoto, Chemical Abstracts. 62, 215e (1965).

Poddar, S. N., K. Dey, J. Haldar, and S. C. Nathsarkar, J ournal of the Indian Chemical Society, 47, 743 (1970).

52

Selbin, J., L. H, Homes, and S. P. McGlynn, Journal of Inorganic and. Nuclear Chemistry, 25. 1359 (19 3*) •

, G. Maus, and D. L. Johnson, Journal of Inorganic and Nuclear Chemistry, 29. 1735 (19o7).

Teyssie, P., and J. Charette, Spectroohlmlca Acta, 19. 1407 (1963).

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Unpublished Materials

Syamal, A. and L. J. Theriot, unpublished data, Department of Chemistry, North Texas State University, Denton, Texas, 1972.