Magnetic and spectroscopic studies on nickel(%$) and copper(I1) complexes of some neutral1 tridentate ON§ ligands

M. AKBAR ALI Department of Chemistry, University of Chittagong, Chittagong, Bangladesh

Received August 2 1, 1979

M . AKBAR ALI. Can. J . Chem. 58,727 (1980). New Schiff base ligands formed from 2-methoxybenzaldehyde and 2,4-dimethoxybenzaldehyde with N-methyl-S-alkyldithio-

carbazates and their nickel(I1) and copper(I1) complexes have been prepared and characterised by elemental analysis and magnetic and spectroscopic measurements. The Schiff bases behave as neutral tridentate chelating agents forming stable nickel(I1) complexes of stoichiometry NiLX2~.~C2H5OH (L = 2-methoxy- or 2,4-dimethoxybenzaldehyde Schiff bases of N-methyl-S-methyldithio- carbazate; X = I-, SCN-; x = 0, 1). Conductivity, magnetic, and spectral data support an octahedral structure for the nickel(I1) complexes. The CuLCl, complexes were also isolated. Magnetic and spectral evidence are in accord with a chloro-bridged dimeric structure. The chloro-compiex of copper(1I) with the 2-methoxybenzaldehyde Schiff base displays a room-temperature magnetic moment of 1.81 BM, which remains virtually constant over the temperature range 343-123 K.

Hydrated copper(I1) chloride promotes complete hydrolysis of the 2,4-dimethoxybenzaldehyde and 2-methoxybenzaldehyde Schiff bases of N-methyl-S-benzyldithiocarbazate with the concomitant formation of copper(I1) complexes of the parent N- methyl-S-benzyldithiocarbazate of general formula, Cu(N-SR)Cl, (R = C6hi,CH2-).

M. AKBAR ALI. Can. J . Chem. 58,727 (1980). On a prepare des nouveaux ligands de bases de Schiff a partir de la reaction du mithoxy-2 et du dimethoxy-2,4 benzaldehyde avec

le N-methyl-S-alkyldithiocarbazate et leurs complexes de Ni(1I) et de Cu(I1) et on les a caracterises par l'analyse elementaire et par des mesures magnetiques et spectroscopiques. Les bases de Schiff se comportent comme des agents chelatants tridentates neutres en formant des complexes stables de Ni(I1) de formule NiLX,.xC,H,OH (L = methoxy-2 ou dimethoxy-2,4 benzaldehyde bases de Schiff du N-methyl-S-alkyldithiocarbazate; X = I-, SCN-; x = 0, 1). La conductivite, les donnees magnetiques et les donntes spectrales sont en faveur d'une structure octaedrique des complexes de nickel. On a egalement isole des complexes de type CuLCI,. Les preuves magnetiques et spectrales sont en accord avec une structure de dimere ayant un chlore en position de pont. Le moment rnagnetique du complexe chlore de Cu(I1) avec la base de Schiff derivant du methoxy-2 benzaldehyde a la temperature ambiante, est 1.81 BM et il reste virtuellement constant sur une echelle de temperature de 343-123 K.

Le chlorure cuivrique hydrate favorise l'hydrolyse complete des bases de Schiff du dimethoxy-2,4 ainsi que du methoxy-2 benzaldehyde et de la N-methyl-S-benzyldithiocarbazate avec la formation concomittante de complexes de Cu(I1) du N-methyI-S- benzyldithiocarbazate apparent6 de formule generale Cu(N-SR)C12 (R = C6H5CH2-).

[Traduit par le journal]

Introduction obtained was mixed with a hot solution of N-methyl-S-methyl- dithiocarbazate (6.8 g) in the same solvent (50 mL). The mix-

Metal complexes of tridentate chelating agents ture was heated on a steam bath for about 30 min and left containing the ONS donor set have received con- standing for about 3 h, whereupon the crystals which had siderable attention over the past few years (1-61, formed were filtered off: mp 145"C, yield 11.0 g. Anal. calcd. for

since some of these ligands have been to C11H14N20S2: C 51.94, 5.55, N 11.01; found: C 52.21, H5.52, N 11.21.

yield copper(I1) complexes with anomalous magnetic properties. As Bart of a general investiga- tion of metal complexes of ligands containing the BNS donor sequence, some nickel(1I) and cop- per(I1) complexes of Schiff bases formed from 2- methoxybenzaldehyde and 2,Cdimethoxybenzal- dehyde with N-methyl-S-alkyldithiocarbazates are presented herein.

All the physical measurements and analytical procedures em- ployed in the present work have been described in detail previ- ously (7).

Preparation ofthe Methoxybenzaldehyde SchifSBase of N- Methyl-S-methyldithiocarbaz&e (ONS)

N-Methyl-S-methyldithiocarbazate was prepared according to the method of Akbar Ali er al. (8). 0-Methoxybenzaldehyde (6.8 g) was dissolved in 95% ethanol (50 mL) and the solution so

Preparatiorl of the 2,4-Dimethoxybenzaldehyde SchiffBase of N-Methyl-S-methyldithiocarbazate (h4eONS)

To a filtered solution of N-methyl-S-methyldithiocarbazate (6.8 g) in hot absolute ethanol (100 mL) was added a solution of 2,4-dimethoxybenzaldehyde (8.75 g) in the same solvent (50 mL). The mixture was heated on a steam bath for about 1 h and allowed to stand overnight. The compound was obtained as creamy white crystals: mp 149°C (yield, 8.0 g). Anal. calcd. for C,2H,,N,0,S,: C 50.68, H 5.67, N 9.85; found: C 50.56, hi 5.71, N 9.67.

Preparation ofihe 0-Methoxybenzaldehyde SchiflBase of N-Methyl-S-benzyldithiocarbazate (ONSBz)

N-Methyl-S-benzyldithiocarbazate was prepared following the method of Akbar Ali and Teoh (8). The Schiff base was prepared by a method similar to that used for the ONS Schiff base except that N-methyl-S-benzyldithiocarbazate was used instead of N-methyl-S-methyldithiocarbazate: mp 203°C (yield, 10.0 g). Anal. calcd. forC,,H,,N,OS,: C41.79, H5.49,N8.48; found: C 61.59, W 5.46, N 8.64.

W8-4042/80/070727-M$O1.00/0 @ 1980 National Research Council of Canada/Conseil national de recherches du Canada

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728 CAN. J . CHEM. VOL. 58 , 1980

Preparation of the 2,4-Dimethoxybenzaldehyde Schiff Base of N-Methyl-S-benzyldithiocarbazate (MeONSBz)

This compound was prepared following the procedure of Bose (9) by using N-methyl-S-benzyldithiocarbazate and 2,4- dimethoxybenzaldehyde. Anal, calcd. for C,,H2,N,0,S2: C 59.97, H 5.57. N 7.77; found: C 60.18, H 5.62, N 7.72.

Preparation of Metal Complexes Unless otherwise stated all the complexes were dried in oacuo

over P401,.

Preparution of Ni(ONSj1, A solution of nickel iodide was first prepared by heating nickel

nitrate hexahydrate (3.0 g) and sodium iodide (3.0 g) in absolute ethanol and filtering off the precipitated sodium nitrate. To this nickel iodide solution was added a solution of the Schiff base (1.5 g) in acetone (100 mL) and the mixture was heated at reflux for ca. 1 h. It was then allowed to cool down to room tempera- ture and the reddish-brown crystals which had formed were filtered off and washed with a little acetone followed by benzene and ether. Anal, calcd. for Cl,HI4N2OS2: C 23.31, H 2.49, Ni 10.36; found: 24.07, H 2.45, Ni 10.10.

Preparation of Ni(ONS)(NCS), A solution of nickel(I1) thiocyanate prepared by heating nick-

el(I1) nitrate hexahydrate (3.0 g) and sodium thiocyanate (3.0 g) in absolute ethanol was mixed with solution of the Schiff base (1.5 g) in a mixture of butanol (20 mL) and 2,2-dimethoxy- propane (I0 mL). The mixture was heated under reflux for about 2 h and the solvents were then evaporated slowly on a steam bath whereby deep green crystals of the complex were obtained. These were filtered off and washed successively with methanol and acetone. Anal. calcd. for C,,H,,N,OS,Ni: C 36.39, H 3.29, Ni 13.69; found: C 36.29, H 3.19, Ni 13.50.

Preparation of Cu(ONSjC1, A solution of copper(I1) chloride dihydrate (1.7 g) in absolute

ethanol (50 mL) was mixed with a solution of the Schiff base (2.5 g) in acetone (100 mL) and the resultant solution was heated on a steam bath until green crystals appeared.

The crystals were filtered off and washed several times with ethanol and acetone. Anal. calcd. for C1,Hl4N2OS2CuCl2: C 33.98, H 3.63, Cu 16.34, C1 18.20; found: C 33.50, H 3.22, Cu 16.70, C1 18.60.

Preparation of Cu(MeONSjC1, The compound was prepared by a similar method as described

for Cu(ONS)Cl,. Anal. calcd. for CI,H,,N,02S2CuC12: C 34.41, H 3.85, Cu 15.17; found: C 34.20, H 3.76, Cu 15.30.

Preparation of Ni(MeONS)I,.C,H,OH Butanol (30 mL) was added to a solution of nickel iodide

(1.4 g) in absolute ethanol (50 mL) followed by the addition of ligand (1.42 g) in acetone (50 mL). The reaction mixture was heated under reflux for ca. 1 hand then allowed to evaporate on a steam bath with occasional addition of acetone. When the volume of the reaction mixture dropped to about 30 mL, some brown crystals began to settle down. At this stage 2,2-di- methoxypropane (10 mL) was added and the mixture further heated on a steambath whereupon the brown crystals formed were filtered off and washed with a few millilitres of acetone followed by benzene. Anal. calcd. for Cl,N2,N,02S,Ni12: C 26.15, H 3.45, Ni 9.13; found: C 26.17, H 2.73, Ni 9.40.

Reactions of ONSBz and MeQNSBz with CuC12~2N20 A solution of the appropriate Schiff Base (ca. 1.7 g) in ben-

zene (50 mL) was mixed with a hot solution of CuCl,.2H20 (1.7 g) in methanol (50 mL) and the reaction mixture was heated under reflux for about 3 h whereupon the green crystals formed were filtered off and washed with benzene and methanol. Anal.

calcd. for C,H,,N,S,CuCI,: C 31.17, H3.50, Cu 18.32, C120.10; found: C 31.44, H 3.45. Cu 18.40, C1 20.55 (for the reaction of MeONSBz with CuCl,). For the reaction of MeONSBz with CuCI,, found: Cu 18.30, C120.45.

Results and Discussion The Schiff bases (1; R = CH, or CH,C,H,; R' =

H or OCH,) were obtained readily by condensation of appropriate aldehydes with N-methyl-S-alkyl- dithiocarbazates.

The metal complexes which were isolated in the present study are presented in Table 1 together with some of their properties. For steric consid- erations the present Schiff bases can act either as ONS tridentates, coordinating via the methoxyl group, the azomethine nitrogen and the thioketo sulphur atoms or as SS bidentates coordinating through the two sulphur atoms. However, previous studies by Akbar Ali et a l , have shown that such ligands prefer ONS coordination to SS coordina- tion (5, 6). Some important ir bands of the Schiff bases and their metal complexes are shown in Table 2. The assignments shown in the table are only tentative and based on comparisons of the ir spectra with those of similar compounds (6,7, 10). Two strong peaks appear at ca. 1600 and 1592 cm-I in the ir spectra of all the present Schiff bases. These are assigned to the C=N stretchings of the azomethine group (6). The shifts of these bands to lowerfrequencies by 10-15 cm-I in the ir spectra of the complexes indicate that bond formation takes place through the azomethine nitrogen atom ( I 1).

A strong band at about 1002 cm-I in the ir spectra of the subject Schiff bases may be attributed to the v(H,c-~) (12-14). This band is also shifted to lower frequencies (Table 2) in the spectra of the metal complexes suggesting that the methoxyl group is also involved in coordination to the metal ions. Further evidence in favour of methoxyl oxygen coordination comes from the presence of a medium to weak band at about 600 cm-I in the spectra of the complexes. This band does not correspond to any ligand band in this region and consequently may be assigned to the metal-oxygen stretching frequency (13).

Bands at ca. 1235 and 942 cm-I in the ir spectra of the Schiff bases may be assigned to the coupled modes of vcs and VCN (6, 7, 10). It has been ob- served in the case of metal complexes of thiocarbo- hydrazide (lo), S-benzyldithiocarbazate (6) and

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TABLE 1. Colour, conductivity, magnetic moments, and electronic spectral data on metal complexes of the Schiff bases

Aa (ohm-' cm2 P e f t Electronic spectral

Compound Colour mol-I) (BM) data (v,,, in kK)

[Ni(ONS)(NCS),] Green 85.1 3.10 9.2, 11.2sh, 14.0

[Ni(ONS)I,] Reddish- 17.3b 3.10 7.8sh, 9.8, ca. 14.8 brown

[Ni(MeONS)I,] . C,H,OH Reddish- 6.4b 3.12 7.0 sh, 8.4, 12.3 sh brown

[Cu(ONS)CI,] Green 23. 6b 1.81 11.4sh, 13.6

[Cu(MeONS)CI,] Dark 13.2b 1.85 13.0br, 20.8 green

[CU(N-SBZ)CI,]~ Green 40.0 1.72 13.3, 24.7

[Cu(N-SBz)Cl,le Green 48.0 1.73 13.3, 24.8

"Molar conductance of ca. 10-'-5 x lo-'' rM solutions in NsV-dimethylformamide. b M ~ l a r conductance in nitromethane. <pen= at 296+ 2 K. dPrepared by the reaction of CuCI,. 2H,O with ONSBz. €Prepared by the reaction of CuCI,. ZH,O with MeONSBz; sh, shoulder; br, broad.

some of its derivatives (7) that these coupled vcs and v m modes in the spectra of the ligands are raised to higher frequencies in the spectra of the complexes. This fact has been attributed to the coordination of the thioketo sulphur which causes an increase in the C-N bond order and nullifies any lowering ofvcs upon coordination (6,7, 10). In the present study, although thevCN + vcs band does not show any appreciable raise in frequency in the spectra of the complexes compared to those in the ligands, the vcs + vcN band is raised to higher frequencies (Table 2), indicating that the thioketo sulphur atom is involved in coordination.

The preceding ir evidence supports the fact that the subject Schiff bases are behaving as ONS tridentates and not as SS bidentates as has been found in the case of similar ligands studied by other workers ( 5 , 6).

The Nickel(4I) Complexes Reaction of the Schiff bases with nickel(I1) iodide

and nickel(I1) thiocyanate in a mixture of ethanol and 2,2-dimethoxypropane resulted in the forma- tion of crystalline complexes of empirical formula, NiLX2-nC2H,0H (where E = ON§, MeONS; X = I- or NCS-; n = 0 or 1). These compounds were found to be stable in a dry atmosphere, but slowly decomposed in the presence of moisture. Attempts to prepare similar iodo- and thiocyanato- complexes of nickel(I1) with the Schiff bases con- taining the benzyi groups on one of the sulphurs were unsuccessful. In each case the unreacted ligands could be isolated almost quantitatively. Similarly all the ligands studied herein failed to yield any complex with nickel(H1) chloride and nick-

el(I1) bromide. The inability of the Schiff bases to produce any complex with nickel in the presence of hard donors such as the chloride and bromide ions seems to suggest that symbiosis phenomenon may be playing a very important role in the formation of the iodo- and thiocyanato-complexes. The nick- el(I1) ion has been termed as a fairly hard ion (15) and consequently, its coordination to soft donors present in the subject Schiff bases would be favoured only in the presence of soft anions such as the iodide and thiocyanate ions which most prob- ably symbiotically motivate the nickel(I1) to act as a soft acceptor.

The presence of ethanol in Ni(MeONS)I,. C,H,OH is confirmed by the presence of a broad band at 3660 cm-I in its ir spectrum. The 0-H stretching frequency generally appears as a broad band at 3660 cm-' in the ir spectrum of free ethanol (16) and this is observed at a lower frequency in coordinated ethanol (17). The presence of 0-H stretch at 3660 cm-I in the ir spectrum of the above iodo-complex is an indication that the ethanol mol- ecule is present as ethanol of crystallization and not as a coordinated ethanol molecule. The conductiv- ity data of all the complexes isolated in the present study are set aside in Table 1.

The nickel(I1) complexes, although show some dissociation in nitromethane, have conductance values much lower than that expected for a uni- univalent electrolyte in this solvent. On the basis of these data the complexes may be formulated as [NikX,]. Support in favour of anion coordination also comes from the ir spectrum of the thiocya- nato-complex. Because of its ambidentate nature, the N G S ion is known to coordinate in different

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CAN. J . CHEM. VOL. 58. 1980

TABLE 2. Infrared absorption frequencies ( c m l ) of the Schiff bases and their metal complexes.

Assignments"

Compound v ~ = ~ v c s + vcs VCS + VCN V(H~C- -0 ) v ( ~ - ~ )

ONS 1602s 1235s 942s 1002s - 1592m

ONSBz

MeONSBz

Assignments

"v and 6 denote stretching and bending modes respective!^. Relative band intensities are denoted by s , m, w, sh, meaning strong. medium, weak, and shoulder respectively.

OPrepared from the reaction of CuCI, 2H,O with ONSBz. 'Prepared from the reaction of CuCI, .2H,O with MeONSBz. "Band positions reported by Akbar A!i and Teoh (7). 'N-SBz denotes N-methyl-S-benzyldithiocarbazate.

modes (18) and ir spectroscopy has been very helpful in distinguishing between these modes (19). The C=N stretching frequency has been observed in the range 2040-2080 cm-I for N-bonded thio- cyanate and in the range 2080-2120 cm-I for S- bonded thiscyanare. A number of metal complexes are known where the C-N stretching frequencies are observed at 30-40 cm-I higher than that in the terminal thiocyanate groups (20-24). This has been attributed to the presence of M-NCS-M bridges. Furthermore, it has been suggested that extensive split"png ofthe band cosresponding to the antisymmet~c stretch occurs in the ir spectra of complexes containing both terminal and bridging thiocyanato-groups (23, 24). The ir spectrum of [Ni(ONS)(NCS),] exhibits two strong bands at 2090 and 2130 cm-I with definite shoulders at 2100

and 2140 ~ m - ~ . This is strong evidence that both terminal and bridging thiocyanato-group are pres- ent. Since the ligand behaves as a tridentate and there are two thiocyanate ions per nickel(H1) ion, a thiocyanate-bridged six-coordinate structure shown below would be in keeping with the ob- served ir and conductivity data.

M n 2

NCS 0 &Ai/ 'd Z~~~'!\S/

n ,/j

The room-temperature magnetic moments of the nickel complexes (Table I) are normal for a six- coordinate nickel(I1) in an octahedral or pseudo- octahedral field (28). The solid reflectance elec-

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AKBAR ALI 73 1

tronic spectral data (Table I ) also support an octa- hedral structure for the present nickel(1I) com- plexes. The spectra exhibit two bands at about 9.9 and 15.0 kK attributable to the transitions 3A2, 3T2,(P) and 3 A 2, + 3Tlg(F) respectively of octa- hedral nickel(1I). The third expected band corre- sponding to the transition 3A2g(F) -+ 3Tlg(P) is probably hidden beneath the charge-transfer band. The presence of donor atoms of unequal field strengths in the ligands is expected to cause some distortion from the regular Oh symmetry with the consequent broadening of the vl and v, bands. A1- though no such splittings have been observed in the present spectra, the vl band has been found to be very broad with definite shoulders. This suggests that some distortion might have been present. On the basis of their stoichiometry, low solubility, electronic spectra, and magnetic moments, a di- meric or a polymeric structure involving the iodo- or thiocyanato-bridge is assigned to the present nickel(1I) complexes. From a comparison of the electronic spectra of the two iodo-complexes, it appears that the ligand field strength of the S - methyl derivative is greater than that of the S- benzyl derivative.

The Coppsr(l1) Complexes The Schiff bases, ONS and MeONS, react with

copper(I1) chloride forming crystalline complexes of general formula, CukCl,, which behave as non- electrolytes in nitromethane. Reactions of these ligands with either copper(1I) perchlorate or cop- per(I1) nitrate under similar conditions did not yield any isolable products. The Schiff bases, however, reacted with copper(1I) bromide yielding some orange products which were found to be diamagne- tic in nature. Since these compounds could not be obtained in an analytically pure form, they are not characterized herein. However, from the diamag- netic nature of these complexes, it can be safely inferred that the subject ligands reduce copper(11) bromide to yield a copper(1) complex. As the Schiff bases behave as neutral OWS tridentates and there are two chloride ions per copper(I1) ion in the coor- dination sphere, the CuEC1, complexes may be thought to possess either a monomeric five- coordinate structure or a dimeric or polymeric chlorine-bnddged structure. The electronic spectra of these complexes (Table 1) display a broad band at ca. 13.5 kK, which do not resemble spectra of other known five-coordinate copper(I1) species 4291, but are close to the spectra of distorted octa- hedral copper(I1) complexes (30). The room tem- perature magnetic moments of the CuLCB, com- plexes are about 1.81 BM which are quite normal for a 3d9 ion. The magnetic susceptibilities of the

Cu(ONS)C12 complex were measured over the temperature range 343-93 K. The compound obeys the Curie-Weiss law of the form shown below, where ~,"O"is the molar susceptibility cor- rected for diamagnetism, Na = 60 x cgs units is the assumed value of the T.I.P., and all the other symbols have their usual meanings.

A plot of IIx,~~"" - Na) vs. T gave a straight line from which the value of the Weiss constant 8 was obtained. 'The small value of the Weiss constant (8 = + 14 K) indicates that the compound is a normal Curie-Weiss paramagnet and there is no appreci- able magnetic interaction in the complex.

When the Schiff bases, ONSBz and MeONSBz, reacted with copper(I1) chloride, instead of the ex- pected Schiff base complexes, the complexes iso- lated were those of the parent N-methyl-S-alkyl- dithiocarbazates. The identities of these complexes were confirmed from the analytical data (Table 1) and from a comparison of their ir, magnetic, and electronic spectral data with those reported by Akbar Ali and Teoh (7). The ir spectra of these complexes do not display the VC=N band of the Schiff bases, but instead they show the VI\IH, and &NH2 bands of the parent amines (Table 2). This shows that in the presence of copper(H1) chloride the Schiff bases are Rydrolysed with the concom- itant formation of copper(I1) complexes of the pa- rent N-methyl-S-alkyldithlosarbazates. In a recent communication (9) it has been claimed that the MeONSBz ligand gives copper(1I) chloride and bromide complexes. This author was unable to isolate the reported complexes by following the procedure reported in the literature (9). Each lime the Schiff bases were found to be hydsolysed re- sulting in copper(1I) complexes of the parent amines. Nickel(I1) (31-34) and copper(1I) (35) have been shown to catalyse the hydrolysis ofehe C=N bond of Schiff bases with the concomitant forma- tion of a metal complex of parent amines. The activation of the azomethine group toward hy- drolytic cleavage may be considered to be analo- gous to the activation of the azo group (36) in the cobalt(I1) catalysed hydrolysis of the latter. The coordination of the azomethine nitrogen facilitates the electron cloud being drawn away from the C=N bond and thereby weakens it, so that it be- comes more susceptible to hydrolytic cleavage. This mechanism is very similar to the intelrpretation provided by Kroll(37) of the catalytic hydrolysis of amino acid esters by heavy metal ions.

Acknswledgemeam~ The author wishes to express his sincere thanks

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to Professor S. E. Livingstone and Associate Ro- fessor K. A. Goodwin of the School of Chemistry, University of New South Wales, Sydney, Australia for their help in connection with some solid reflec- tance spectra. Thanks are also due to the School of Chemical Sciences, Universiti Sains Malaysia, Penang, Malaysia and the Department of Chemis- try, University of Chittagong, Bangladesh for the provision of some facilities for this work.

M. AKBAR ALI and S. E . L~VINGSTONE. k d . Chem. Rev. 13, 101 (1974). M. AKBAR ALI, S. E. LIVINGSTONE, and D. J . PHILLIPS. Chem. Commun. Chem. Soc. London, 909 (1972). M. AKBAR ALI, S . E. LIVINGSTONE, and D. J. PHILLIPS. Inorg. Chim. Acta, 7, 179 (1973). M. AKBAR ALI. S. E. LIVINGSTONE, and D. J. PHILLIPS. Inorg. Chim. Acta, 7,531 (1973). M. AKBAR ALI and R. BOSE. J. Inorg. Nucl. Chem. 39.265 (1977). M. AKBAR ALI and S. 6. TEOH. J. Inorg. Nucl. Chem. 40. 2013 (1978). M. AKBAR ALE and S. G. TEOH. J. Inorg. Nucl. Chem. 40. 451 (1978). M. AKBAR ALI. S. E. LIVIKGSTONE, and D. J . PHILLIPS. Inorg. Chim. Acta, 6, 11 (1972). R. N. BOSE. Inorg. Nucl. Chem. Lett. 14. 193 (1978). 6 . R. BURNS. Inorg. Chem. 7,277 (1968). J. E. MOVACIC. Spectrochim. Acta, 23A, 183 (1967). F. K. BATCHEW, W. GERRARD, E. F. MOONEY, R. G. REES, and H. A. WILLIS. Spectrochim. Acta, 20,51(1964). Y. KAWASAKI and R. OKAWARA. J. Inorg. Nucl. Chem. 27, 1168 (1965). R. OKAWARA and M. WADA. J. Organomet. Chem. 1, 81 (1965). L . SACCONI. Trans. Met. Chem. 4, 199(1968).

6 . M. BARROW. J . Chem. Phys. 20,1739(1952). R. C. DICKIKSOK andG. J. L o ~ G . J. Inorg. Nucl. Chem. 36, 1235 (1974). R. A. BAILEY. S. L . KOZAK, T. W. MICHELSON. and M. N. MILLS. Coord. Chem. Rev. 6,407 (1971). K. NAKAMOTO. Infrared spectra of inorganic and coordi- nation compounds. 2nd ed. Wiley-Interscience, New York. 1970. W. J. DAVIS and J . S ~ ~ I T H . J . Chem. Soc. A, 317 (1971). G. CONTRERAS and R. SCHMIDT. J. Inorg. Nucl. Chem. 32, 127 (1970). R. S. TOBIAS. Inorg. Chem. 9.2682 (1970). A. R. DAVIS. C. J . MURPHY, and R. A. PLANE. Inorg. Chem. 9,423 (1970). S. M. NELSON and A. RODGERS. Inorg. Chem. 6, 1390 (1967). L . SACCONI, I. BERTINI. and F. MAN. Inorg. Chem. 6,262 (1967). A. SABATIN~ and 1. BERTIKI. Inorg. Chem. 4,959 (1965). J. CHATT and L. A. DUNCANSON. Nature, 178.997 (1965). C. J. BALLHAUSEN. Introduction to ligand field theory. McGraw-Hill, New York. 1962. M. AKBAR ALI, S. E. LIVINGSTONE, and D. J . PHILLIPS. Inorg. Chim. Acta, 6,39 (1972). A. B. P. LEVER. Inorganic electronic spectroscopy. Elsevier, Amsterdam. 1968. G. L. EICHHORN and J. C. BAILAR. J . Am. Chem. Soc. 75, 2905 (1953). R. K. Y. HO and S. E. L I V I ~ G S T O N E . Aust. J. Chem. 18, 659 (1965). L . T. TAYLOR, F. L. URBACH, and D. H. B u s c ~ . J. Am. Chem. Soc. 91. 1072(1969). M. DAS and S. E. LIVINGSTONE. Inorg. Chim. Acta, 19, 5 (1976). C. M. HARRIS, S. L. LENZER, and R. L. MARTIN. Aust. J. Chem. 14.420 (1961). R. PRICE. .I. Chem. Soc. A, 521 (1967). H. KROLL. J. Am. Chem. Soc. 74,2036(1952).

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