Electronic spectra of tetrahedral CoII complexes with thiourea and its derivatives and with triphenyl-phosphine

Journal of Molecular Structure, 19 :1973) 447-454 0 Eisevier Scientific Publishing Company, Amsterdam -Printed

in The Netherlands

ELECTRONIC SPECTRA OF TZTRAHEDRAL Co’l COMPLEXES WITH THIOUREA AND ITS DEI1IVATIVES AND WITH TRIPHENYL PHOSPHINE FLORIAN

PRUCHNIK

Institute of Chemistry,

University of Wrocbw,

Wroclaw (Poland)

ABSTRACI’

The electronic spectra of CoClZL2 (L = triphenylphosphine, thiourea, phenylthiourea and N,N’-diphenylthiourea) have been examined. The parameters Dq and B were calculated and tentative structures of the green and blue forms of the complex dichlorobis(N,N’-diphenylthiourea)coba.lt are proposed on the basis of electronic and infrared spectra.

INTRODUCTION

In order to determine the structure and properties of cobalt(I1) complexes with thiourea and its derivatives, the electronic and infrared spectra of Co I1 complexes with thiourea, N-phenylthiourea and diphenylthiourea were examined. It is known 1 that N,N’-diphenylthiourea forms two compounds of the formula Co( diPhtu), ‘+ with cobalt(H), one blue and the other brown. Their electronic spectra vary in the transition range 4?1 (F) + 4A 2 for Td symmetry. These compounds, however, were not obtained as solids, because they do not crystallize from solutions with excess NJV’diphenylthiourea. EXPERIMENTAL

All compounds were obtained by concentration of solutions containing stoichiometic amounts of the hydrated cobalt chloride and the appropriate ligand.

Preparation

of CoCl,(tu),

Concentrated solutions of stoichiometric amounts of hydrated cobalt chloride and of thiourea in ethanol were prepared; the solutions were mixed and then evaporated under reduced press-&e-at robm temperature until the complex crystallized. The complex was then recrystallized from acetone. Analysis for CoCIZ C, S,N,Ha : Calculated: Co, 20.89%; C, 8.51% H, 2.86% Found: Co, 21.16%; C, 8.85%; H, 3.27%

448

Preparation of CoCl, (Phtu), - C,H,O, An acetone solution of stoichiometrid amounts of cobalt chloride and IV-phenylthiourea was concentrated by evaporation on a water bath. Dioxane was then added and the mixture was re-evaporated. Finally, the solution was concentrated under vacuum at room temperature, and stirred with a magnetic stirrer. The precipitate was filtered and washed with ethyl ether and with dioxane and dried under vacuum. Analysis for COCI,C,,H,~N~O,S,: Calculated: C, 41.37%; H, 4.63%; Co, 11.27% Found: C, 41.68%; H, 5.10%; 10.69% Preparation of CoCl,(diPhtu), An acetone solution of stoichiometric amounts of cobalt chloride and N,N’-diphenylthiourea was heated on a water bath until the initial blue colour became green. During evaporation, the blue compound was obtained first; it was isolated from the solution and washed with acetone, ethyl ether and lastly with acetone. On further concentration the green ccmpound was obtained, which was washed with ethyl ether. Both compounds were recrystallized from acetone. The blue compound crystallized with a solvating acetone molecule which it lost spontaneously upon standing in air. Analysis for COC~~C&H~~N~S~: Calculated: C, 53.25%; H, 4.13%; N, 9.55%; Co, 10.05% Found: C, 52.99%; H, 4.37%; N, 9.20%; Co, 10.26% (green compound) C, 52.98%; H, 4.60%; N, 9.22%; Co, 9.87% (blue compound)

Preparation of COCI~(PP~~)~

The compound was obtained by concentration of d hot solution of cobalt chloride and trimethylphosphine in ethanol and was recrystallized from benzene. Analysis for CoC12P, C, e Ha c : Calculated: C, 66.07%; H, 4.62%; Co, 9.01% Found: C, 64.85%; H, 4.65%; Co, 9.04% All attempts to prepare the similar compound with IV-allylothiourea in several solvents failed because tarry compounds were formed. The electronic and infrared spectra were recorded on Unicam SP-700 and Cary 14 spectrophotometers and on Perkin-Elmer 621 and UR-20 Carl Zeiss Jena spectrophotometers, respectively. Chromatographic determinations were carried out using an Elpo N-503 chromatograph. RESULTS

AND DISCUSSION

The position of the absorption bands of the compounds with thiourea and its derivatives depends on the concentration of the solution (Table 1, Fig. 1). For dilute solutions (10-d M) shifting of the bands towards higher energies is observed. For concentrations greater than 3 X 10-s M, no band shifting

)2

7500(36)

5900(36)

5300(93), 6200, 7400(55)

5300(95), 6100, 7500(57)

5300(85), 6300, 7400(52)

13,950(396) 15,000(462) 16,200(427)

5300(106), 6300, 7500(70)

14,500( 302) 15,300(294) 16,800(286)

15,100(120), 15700, 16,200, 17,200(70)

14,100( 320) 15,000(400) 15,900(408)

15,100(160), 15,700, 16,200, 17,300(140)

14,000( 350) 15,000(410) 15,900(420)

14,900, 15,600(182) 16,200, 17,200

13,900(292) 14,900( 348) 16,000(355)

14,300,14900(235) l&600(261), 17800

(cm’-‘)

v3

(cm-l)

v2

a tu Elthiourea, Phtu = N-phenylthiourea, diPhtu = NJ’-diphenylthiourea,

Coa,(PPh,

Co(diPhtu)2C12 (blue)

Co(diPhtu),Cl (green)

Co(Phtu)2ClP. C,H,O,

Co(tu)&

Compound*

e values are given in parentheses

Acetone

Ethanol

Acetone

22,300

36,200(36,300)

Ethanol

Acetone

23,000

24,000 36,000(41,200)

Ethanol

Acetone

22,000(7.0)

37,200(22,300), 41,500(15,100)

Ethanol

Acetone

Solvent

33,000(795) 41,000(28000)

22,200( 5.1)

Other bands

TABLE 1 Electronic spectra of cobalt II complexes with triphenyl-phosphine, thiourea and its derivatives

450

r

A

lW0

SC0

4400

Icm-

‘3

laa

1600

4400 [cm-l]

T-

8

r

Fig. 1. Electronic spectra of the blue and green isomers of CoClz(diPhtu)z in acetone at ) Bleu CoClz(diPhtu)z; (------) green CoClz(diPhtu)z. (A) c various concentrations. (M, d = 2 cm;(B) c = 1.01 X lo-’ M, d = 0.1 cm. = 0.96 X lOa

towards lower frequencies was observed. For this reason, the electronic spectra of the compounds with thiourea ligands were measured using solutions of equal concentration’( 10e2 M approximately). The spectrum of dichloro(triphenylphosphine) cobalt in acetone solution is very different from the spectrum of monocrystals of that compound and from the spectrum in methylene chloride2~3. These changes may result from strong solvation of molecules of the complex or, more probably, from the partial substitution of coordinated ligands by solvent molecules. The latter possibility was confirmed by the fact that the spectra of these compounds in ethyl alcohol have a band at higher frequencies (over 17,000 cm-l). This band may result from the 4Tl, (F) j4Tlg (P) transition in the octahedral complex formed. In methanol, the complete formation of octahedral complexes follows rapidly with a change in colour to rose. In the case of the cobalt compounds with N-phenylthiourea and N-allylothiourea, tarry (probably macromolecular) compounds readily arise and hydrogen bonding N-H---N, N-H---phenyl, N-H---ally1 could play an essential role in these cases. The intramolecular interaction ceases when the compound crystallizes with a solvent molecule. This was confirmed by the fact that when ‘CoC12(Phtu)2C4HS02 was washed with a large amount of ether, the diox-

451

ane molecules were removed and a tarry compound again formed. The presence of dioxane molecules in the compound with N-phenylthiourea and of acetone in the blue form of CoC12 (diPhtu)z was confirmed by characteristic bands in the IR spectrum (at 867, 1045, 1080, 1116,1253 and 1695 cm-l, respectively) and by gas-liquid chromatography. The removal of the acetone molecule had no effect on the colour of a complex with i’V,N’-diphenylthiourea. The electronic spectra of tetrahedral and pseudotetrahedral cobalt(II) complexes are characterized by complicated splitting of the ligand field bands 4A2 --f a,b 4Tl or 4T1(F), *T,(P) which may be caused by several factors: by orbital splitting caused by symmetry lowering of a complex, by spin-orbital interaction, by splitting of orbital degenerate states caused by the dynamic Jahn-Teller effect, etc. In some complexes the orbital splittin is the decisive factor, e.g. the spectrum of the CoCl, (PPha), crysta12*8 exhibits almost complete polarization along the axes X, y or z. In other complexes the orbital splitting is less essential and partial polarization is observed5. Similar splitting was also observed for the tetrahedral cobalt(I1) complexes. This being so, the average values of 1ODq and B were calculated from the position of the centre of gravity of bands v2 and v3 under the assumption of tetrahedral symmetry6-g. The 1ODq values obtained by us are lower than those reported by Piovesana and Furlani 10 and by Cotton et al. 6 s7. The spectra in acetone solutions recorded by them at relatively low concentrations exhibited bands at frequencies higher than the bands reported here. In some cases the bands in the visible and in the near IR were recorded for the same compounds at various concentrations. Obviously, a change in concentration caused various band shifts. An analogous dependence of the band position on concentration has TABLE

2

Electronic structure parameters of pseudotetrahedral Co II complexes and stretching frequency ~cO-s Compound

1ODq

B

(cm-l)

(cm-1

)

P

vCO-S

3500

725

0.74

247, 277

- C,H,O,

3450

735

0.75

240 272

Co(diPhtu),Cl,

green

3450

750

0.77

288

Co(diPhtu),C12

blue

3450

745

0.76

277= 275 282

3950

720

0.74

Co(Phtu),Cl,

WPPh,

)#,

B for gaseous Co2+ ion = 976 cm-l, fi = B/976. a Value for Co(diPhtu)2C12 - CH, COCH,.

452

been found by Yagupsky et al. l1 for tetracoordinated complexes of Co(NCS),(tu), (tu = thiourea and its derivatives)_ The splitting parameter 1ODq for the complex with thiourea is slightly higher with respect to the remaining compounds (Table 2). In contrast, the B values are high&t for N,N’-diphenylthiourea. Relatively low 1ODq values and similarity of the bands indicate the presence of Co-S bonding in all complexes examined. The spectra of the green and blue forms of the complex with NJV’diphenylthiourea in the range of v2 and v3 are in fact, identical_ The difference in colour is caused by the higher absorption in the range 19,000-25,000 cm-l of the green compound compared with the blue one. The infrared spectra of both compounds vary very little (Fig. 2, 3, Table 2). The essential differences are observed in the range of the v N-H stretching bands. Yagupsky and Levitus 1 have found the existence of two Co(diPhtu), (ClO, )2 isomers (blue and brown) which exhibited very different spectra in the range 40008000 cm-l. The ligand in the brown compound is coordinated in form I, whereas in the blue compound in form II. Ph-N H-N

/H \ /

Ph-N

c-s .

P&-d

‘Ph I

n

/H \

IPh

H-

Y

c-s H-N

‘H

/

c-s

‘Ph

m

Isomer I is formed upon standing in acetone solution and could be isolated as a solid by the slow evaporation of acetone.

Fig. 2. IFLspectra of the green CoCl2(diPhtu)~ and CoClz(diPtu)~-CH~COCH3 CoC12CdiPhtu)z:CH3COCH3 (blue): &d hexachlortibutadiene. ( -) Coclz (diitu)z (green).

in Nujol ( -1

453

i

i ::, ; i:

:?j’

i:, .:

::I

:! : ::- :; j... : i_: : : : : : ; :: :: v’

-1,

Fig. 3. 1; spectra ofTobalt(I.I) (diPhtu)z -CH3COCH3 CQClz CcQ(diPhtu)2 (blue). (B) ( -)

complexes\th thiourerand its derivatives. (A) ((blue); (------) CM212(diPhtu)z (green); (o-.---o-‘, CoCl*(tu)* ; (------ ) CoClz(Phtu)z-C~HsO~.

The presence of a large number of bands in the IR spectrum in the ranges 700-900 and 3000-3400 cm-1 of the compound recrystallized from acetone has been assumed to be proof of the formation of the iosmer I (no symmetry in the molecule). In acetone solution this compound forms the brown complex at once, whereas isomer II gives the blue compound which turns brown after some time. The coordination III or I and II simultaneously cannot be excluded. Both green and blue forms of CoClz(diPhtu)s keep their colour in acetone solution at room temperature even after .a couple of weeks. On the basis of the infrared spectra, it’could be assumed that the green and blue dompounds

454

have the l&and coordinated in forms I and II, respectively (Fig. 2). The VC~-_S frequencies (Table 2, Fig. 3) for Cyclic and CoCls(Phtu)a. C,H,O, are almost equal and lower than for the two remaining compounds. REFERENCES 1

G. Yagupsky and R. Levitus, Inorg. Chem.. 4 (1965) 1589. C. Simo and S.L. Holt, Inorg. Chem., 7 (1968) 2655. M. Goodgame and F.A. Cotton, J. Amer. Chem. Sot., 84 (1962) 1543. 4 A.A.G. Tomlinson, C. BelIitto, 0. Piovesana and C. Furlani, J. Chem. Sot. Dalton, (1972) 350. 5 A. Flamini, L. Sestili and C. Furlani, Znorg. Chim. Acta, 5 (1971) 241. 6 F.A. Cotton, D.M.L. Goodgame and M. Goodgame, J. Amer. Chem. Sot., 83 (1961) 4690. 7 F.A. Cotton, 0-D. Faut and J.T. Mague, Inorg. Chem., 3 (1964) 17. 8 A.B.P. Lever a?d SM. Nelson, J. Chem. Sot. A, (1966) 859. Elsevier, Amsterdam, 1968, pp9 A.B.P. Lever, Inorganic Electronic Spectroscopy, 322-328. 10 0. Piovesana and C. Furlani, J. Inorg. Nucl. Chem., 30 (1968) 1249. 11 G. Yagupsky, R.H. Negrotti and R. Levitus, J. Inorg. Nucl. Chem., 27 (1965) 2603. 2 3