cobalt(ii), rhodium(iii), and iridium(iii) complexes of 1,2-dithiocyanatoethane

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Inorg. Phys. Theor. Cobalt(ii), Rhodium(iii), and Iridium(ii1) Complexes of I ,2-Dithiocyanato- ethane By D. C. Goodall, School of Chemistry, The University, Leeds 2 1.2-Dithiocyanatoethane forms polynuclear complexes with cobalt(l1) halides, of general formula [CoX,*L] (X = CI, Br, or I), which are decomposed completely by unidentate ligands. Rhodium(1li) and iridium(ll1) form binuclear halogen-bridged complexes of general formula [MX,.L] (M = Rh or Ir; X = CI, Br, or I). The halogen- bridges are split by unidentate ligands. Infrared spectra are recorded, and structures of the complexes discussed. THE present work investigates the chelating ability of 1,2-dithiocyanatoethane, and gives some insight into the inherent donor properties of the sulphur and nitrogen ends of the thiocyanate group in a neutral environment. Cobalt (11) halides react with 1,2-dithiocyanatoethane under anhydrous conditions to form complexes of the type [CoX,*L], which are stable indefinitely in dry air, but hydrolyse readily. They decompose instantly, yielding the free ligand, when added to water, ammonia, or pyridine. The complexes are generally insoluble in organic solvents. The solid reflectance spectra were studied over the range 370-850 mp. The complexes show a band around 505 mp, which suggests octahedrally co-ordinated cobalt(II), as do their pink or red colours. This main band, which is the only one discernible, may be assigned to the *T1 4A, transition. The magnetic moments, which are in the region 4.94-5.04 R.M., indicate high-spin octahedral cobalt (11). The principal bands in the infrared spectrum of the chloro-complex are shown in Table 2, and are compared with those of the ligand. The bromo- and iodo- complexes have spectra almost identical with that of the chloro-complex. Evidence shows that 1,3-di- substituted ethanes exist in the trans- and gauche-forms in solutions, but only in the tram-form in the solid st ate. Quagliano and his co-workers1 describe a complex of platinum(r1) with 1 ,%dithiocyanatoethane, in which the ligand is shown to exist in the gauche-form necessarjr for chelat ion. The changes observed in some of the fundamental vibration frequencies of 1,2-dithiocyanatoethane on complex-formation with cobalt (11) are quite different from those reported for the platinum complex. In the infrared spectra of the cobalt complexes, there is only a slight change in the pattern of bands in the region 760- 600 cm.-l as compared with the ligand, but the thio- cyanate C-N stretching vibration is shifted by 50--60 cm.-l. It is inferred that the ligand exists in a slightly distorted tram-form in these complexes. The ligand cannot be acting as a chelate, and in view of their general insolubility the complexes are almost certainly polymeric. Similar properties have been observed in bis- (fi-toluidine) dithiocyanatocobalt (11) ,, which is con- sidered to be polymeric, owing to the presence of bridg- ing thiocyanate groups. Since the C-N Stretching vibration is affected much more than the C-S vibrations in the cobalt complexes with 1 ,%dithiocyanatoethane, it is likely that the ligand S. Mizushima, I. Ichishima, I. Nakagawa, and J. V. Quagliano, .J. Phys. Chem., 1955, 59, 293. F. A. Cotton and R. H. Holm, J. Amer. Chem. SOL, 1960, 82, 2983. bonds to cobalt through nitrogen. However, cobalt lies in the border region between class (b) and class (a) metals, according to the classification of Chatt,3 and it is quite likely that co-ordination within the polynuclear cobalt complex occurs through nitrogen and sulphur. Rhodium(II1) and iridium(II1) form a series of dia- magnetic insoluble complexes with l ,2-dithiocyanato- ethane, of the type [MX3*Lj, which are dimeric and non- conducting in dimethyl sulphoxide. They are much more stable than the cobalt complexes. The principal bands in the infrared spectra of the chloro-complexes are shown in Table 2. The bromo- and iodo-complexes have very similar spectra. It is concluded that, in these complexes, 1,2-dithio- cyanatoethane is present in the gaztche-form and is acting as a chelate.1 The C-N stretching vibration of the ligand is hardly affected by complex-formation. This indicates that co-ordination takes place through the sulphur atoms. Two bands observed in the far-infrared spectrum of the chloro-complex (in the case of iridium) suggest the presence of tram chlorine atoms4 The corresponding rhodium complex has three bands, the one at 244 cm.-l suggesting a bridging Rh-C1-Rh group.5 Since the complexes are binuclear, it seems likely that halogen-bridges are present. It has been possible to split these bridges by treating the complexes with pyridine or ;h-t oluidine. x x X x x X In view of the facts so far presented, these binuclear complexes are considered to contain octahedrally TABLE 1 Cobalt(iI),rhodium(m), and iridium(1ir) complexes with lt2-dithiocyanatoethane Magnetic Decomp. moment (B.M.) Complex Colour Pt. (at 20") [CoCI,-L], ... Pink 1 69- 1 7 3 " 4.97 [CoI,*L], ... Red 184-192 4.94 [RhCI,-L], . .. Light brown > 250 0 [CoBr,.L], ... Pink 175-182 5-04 [RhBr,.L],. . . Brown ,I [RhI,*L], .. . Orange ,, [IrCI,.L], ... Pale yellow [IrBr,*L], .. . Yellow 8, [IrI,*L], . . . . .. Brown , S. Ahrland, J. Chatt, andN. R. Davies, Quart. Rev., 1958,l2, 265. 4 J. M. Jenkins and B. L. Shaw, J. Chem. Soc., 1965, 6789. 5 J. Powell and B. L. Shaw, Chem. Comm., 1966, 323. Published on 01 January 1967. Downloaded by Brown University on 30/10/2014 21:23:16. View Article Online / Journal Homepage / Table of Contents for this issue

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Page 1: Cobalt(II), rhodium(III), and iridium(III) complexes of 1,2-dithiocyanatoethane

Inorg. Phys. Theor.

Cobalt(ii), Rhodium(iii), and Iridium(ii1) Complexes of I ,2-Dithiocyanato- ethane By D. C. Goodall, School of Chemistry, The University, Leeds 2

1.2-Dithiocyanatoethane forms polynuclear complexes with cobalt(l1) halides, of general formula [CoX,*L] (X = CI, Br, or I ) , which are decomposed completely by unidentate ligands. Rhodium(1li) and iridium(ll1) form binuclear halogen-bridged complexes of general formula [MX,.L] (M = Rh or Ir; X = CI, Br, or I). The halogen- bridges are split by unidentate ligands. Infrared spectra are recorded, and structures of the complexes discussed.

THE present work investigates the chelating ability of 1,2-dithiocyanatoethane, and gives some insight into the inherent donor properties of the sulphur and nitrogen ends of the thiocyanate group in a neutral environment. Cobalt (11) halides react with 1,2-dithiocyanatoethane under anhydrous conditions to form complexes of the type [CoX,*L], which are stable indefinitely in dry air, but hydrolyse readily. They decompose instantly, yielding the free ligand, when added to water, ammonia, or pyridine. The complexes are generally insoluble in organic solvents. The solid reflectance spectra were studied over the range 370-850 mp. The complexes show a band around 505 mp, which suggests octahedrally co-ordinated cobalt(II), as do their pink or red colours. This main band, which is the only one discernible, may be assigned to the *T1 4A, transition. The magnetic moments, which are in the region 4.94-5.04 R.M., indicate high-spin octahedral cobalt (11).

The principal bands in the infrared spectrum of the chloro-complex are shown in Table 2, and are compared with those of the ligand. The bromo- and iodo- complexes have spectra almost identical with that of the chloro-complex. Evidence shows that 1,3-di- substituted ethanes exist in the trans- and gauche-forms in solutions, but only in the tram-form in the solid st ate. Quagliano and his co-workers1 describe a complex of platinum(r1) with 1 ,%dithiocyanatoethane, in which the ligand is shown to exist in the gauche-form necessarjr for chelat ion.

The changes observed in some of the fundamental vibration frequencies of 1,2-dithiocyanatoethane on complex-formation with cobalt (11) are quite different from those reported for the platinum complex. In the infrared spectra of the cobalt complexes, there is only a slight change in the pattern of bands in the region 760- 600 cm.-l as compared with the ligand, but the thio- cyanate C-N stretching vibration is shifted by 50--60 cm.-l. I t is inferred that the ligand exists in a slightly distorted tram-form in these complexes. The ligand cannot be acting as a chelate, and in view of their general insolubility the complexes are almost certainly polymeric. Similar properties have been observed in bis- (fi-toluidine) dithiocyanatocobalt (11) ,, which is con- sidered to be polymeric, owing to the presence of bridg- ing thiocyanate groups.

Since the C-N Stretching vibration is affected much more than the C-S vibrations in the cobalt complexes with 1 ,%dithiocyanatoethane, i t is likely that the ligand

S. Mizushima, I. Ichishima, I. Nakagawa, and J. V. Quagliano, .J. Phys. Chem., 1955, 59, 293.

F. A. Cotton and R. H. Holm, J . Amer. Chem. SOL, 1960, 82, 2983.

bonds to cobalt through nitrogen. However, cobalt lies in the border region between class (b) and class (a) metals, according to the classification of Chatt,3 and it is quite likely that co-ordination within the polynuclear cobalt complex occurs through nitrogen and sulphur.

Rhodium(II1) and iridium(II1) form a series of dia- magnetic insoluble complexes with l ,2-dithiocyanato- ethane, of the type [MX3*Lj, which are dimeric and non- conducting in dimethyl sulphoxide. They are much more stable than the cobalt complexes. The principal bands in the infrared spectra of the chloro-complexes are shown in Table 2. The bromo- and iodo-complexes have very similar spectra.

It is concluded that, in these complexes, 1,2-dithio- cyanatoethane is present in the gaztche-form and is acting as a chelate.1 The C-N stretching vibration of the ligand is hardly affected by complex-formation. This indicates that co-ordination takes place through the sulphur atoms.

Two bands observed in the far-infrared spectrum of the chloro-complex (in the case of iridium) suggest the presence of t r a m chlorine atoms4 The corresponding rhodium complex has three bands, the one at 244 cm.-l suggesting a bridging Rh-C1-Rh group.5

Since the complexes are binuclear, it seems likely that halogen-bridges are present. It has been possible to split these bridges by treating the complexes with pyridine or ;h-t oluidine.

x x X

x x X In view of the facts so far presented, these binuclear

complexes are considered to contain octahedrally

TABLE 1 Cobalt(iI), rhodium(m), and iridium(1ir) complexes with

lt2-dithiocyanatoethane Magnetic

Decomp. moment (B.M.) Complex Colour Pt. (at 20")

[CoCI,-L], ... Pink 1 69- 1 7 3 " 4.97

[CoI,*L], ... Red 184-192 4.94 [RhCI,-L], . . . Light brown > 250 0

[CoBr,.L], . . . Pink 175-182 5-04

[RhBr,.L],. . . Brown , I

[RhI,*L], . . . Orange ,, [IrCI,.L], . . . Pale yellow [IrBr,*L], . . . Yellow 8 ,

[IrI,*L], . . . . . . Brown ,

S. Ahrland, J. Chatt, andN. R. Davies, Quart. Rev. , 1958,l2, 265.

4 J. M. Jenkins and B. L. Shaw, J . Chem. Soc., 1965, 6789. 5 J. Powell and B. L. Shaw, Chem. Comm., 1966, 323.

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Page 2: Cobalt(II), rhodium(III), and iridium(III) complexes of 1,2-dithiocyanatoethane

204 J. Chem. SOC. (A), 196'7

TABLE 2 lnfrared frequencies assigned to the fundamental vibrations

of 1,2-dithiocyanatoethane (L) and its complexes with cobalt, rhodium, and iridium

L [CoCl,*L], [RhCI,*L], [IrCI,-Lj, trans v(C-S) ...... 659m 667m trans v(C-S) ...... 680m

711m trans CH, rock ... 746s 758m gauche CH, rock.. . 847s 844s gauche CH, rock.. . 920m 920m gauche v(C-C) ...... 1047m 104Sm gauche CH, twist 1105m 1106m trans CH, twist ... 1140m 11401n trans CH, wag ... 1220s 1220s

gauche CH, bend 1412s 1414s trans CH, bend ... 1421s 1419s trans v(CfN) ...... 2150s

gauche CH, wag ... 1284m 1284m

gauche v(CEN) ...... 2165s 2167s v(C=N) (co-ord.) ... 2210s v(C-11) ............... 2 9 6 0 ~ 2975sh 2962w 2966%.

3145s 3141s TABLE 3

Metal-halogen frequencies assigned for the complexes of lJ2-dithiocyanatoethane with rhodium and iridium

[RhCl,*L], .................................... 333sh, 273m, 244m [RhC1,L(p-CH,*C,H,*NH2)] ............ 330m, 276sh [RhCl,L(C,H,N)] ........................... 328m, 278m [IrCl,-L], .................................... 312m, 277sh [IrC1,L(p-CH,C,H,.NH2)] ............... 314m, 276m [IrCl,L(C,H,N)] ........................... 312m, 275m

Complex v(M-C1)

co-ordinated metal atoms, as shown (L = 9-toluidine or pyridine; M = Rh or Ir; X = C1, Br, or I).

1,Z-Dithjocyanatoethane shows no tendency to form complexes with nickel(I1). With palladium(II), products of indefinite composition were obtained, and they all contained only very small amounts of the ligand. EXPERIMENTAL

Cobalt (11) chloride (1.3 g.) and 1.2-dithiocyanatoethane (1.5 g.) were refluxed in dry acetone (15 ml.) for 4 hr. The reaction flask was protected from the atmosphere by phosphorus pentoxide tubes. The microcrystalline complex (2-3 g.) was filtered off, washed with dry ether, and placed in a drying pistol a t 60" for 4 hr. (Found: C, 17.65; H, 1.25; Co, 21.5; N, 10.4. C,H4Cl,CoN2S, requires C, 17.5; H, 1.45; Co, 21-5; N, 10.2y0). Similarly prepared were the bromo-complex (Found: C, 13-2; H, 1.4; Co, 16.25; N, 7-8. C,H,Br,CoN,S, requires C, 13.2; H, 1-1; Co, 16.15; N, 7.7y0), and the iodo-complex (Found: C, 10.4; H, 1.2; Co, 12.85; N, 6.15. C,H,CoI,N,S, requires C, 10.5; H, 0.9; CO, 12.9; N, 6.1%).

rhodium(II1) .-Rhodium trichloride trihydrate (0.26 g.) and lJ2-dithiocyanatoethane (0.20 g.) were refluxed in 2-meth- oxyethanol (20 ml.) for 2 hr. The complex (0.26 g.) was filtered off, and purified by precipitation with ethanol from its dimethyl sulphoxide solution [Found: C, 13-7; H, 1.25; C1, 29.95; N, 8.0%; M (cryoscopy in sulpholan),

7.9% ; M , 7071. Similarly prepared was the brornoconzplex (Found: C, 9.9; H, 0.9; Br, 49.1; N, 5.7. C,H,Br,N,Rh,S, requires C, 9.85; H, 0.8; Br, 49.3; N, 5.75%).

rhodiunz(II1) .-The chloro-complex (0.10 g . ) and sodium iodide (0.35 g.) were refluxed in methyl ethyl ketone (25 ml.)

Dichloro- (1,2-dilhiocyanatoethane) cobalt (11) .-

D i-p-chlorotetrachlorobis- ( 1,2-dithiocyanatoethane) di-

772. C8H,C16N4Rh2S4 requires c, 13.6; H, 1.15; c1, 30.1 ; N,

Di-p-iodotetraiodobis- ( 1,2-dithiocyanatoethane) di-

for 14 hr. The complex (0.16 g.) was filtered off and purified as above (Found: C, 7.7; H, 0.9; I, 60.9; N, 4.5. C8H81,N,Rh,S, requires C, 7.65; H, 0.65; I, 60.66; N,

Trichloro- (1 , 2-dithiocyanatoethane)-p-toluidz'nerhodium( 111).

-Di-p-chlorotetrschlorobis- ( 1,2-dithiocyanat0ethane)di- rhodium(II1) (0.1 g.) and p-toluidine (0.1 g.) were refluxed in methyl ethyl ketone (20 ml.) for 6 hr. The complex (0.12 g.), m. p. >250°, was filtered off, washed with ether, and dried a t 110" for 2 hr. (Found: C, 28.75; H, 2.9; C1, 23.2; N, 9.15. CllH1,C1,N,RhS, requires C, 28.65; H, 2.8; C1, 23.1 ; X, 9.1 yo). Similarly prepared was trichloro- (1,2-dithiocyanatoetJztane)~~ridinerhodium(~~~), m. p. > 250" (Found: C, 25.0; H, 1-95; C1, 24-45; N, 9-7. C,H,Cl,N,RhS, requires C, 24.95; H, 2.1; C1, 24-0; N, 9.7%).

iridium( 111) .-Chloroiridic acid (0.23 g . ) and 1,2-dithio- cyanatoethane (0- 10 g.) were refluxed in 2-methoxyethanol (20 ml.) for 1& hr. The com9lex (0-18 g.) was filtered off, and purified by precipitation with ethanol from its dimethyl sulphoxide solution [Found: C, 10.8; H, 1-0; C1, 24-1; N, 6.35%; Id (cryoscopy in sulpholan), 949. C,H,C1&,N,S, requires C, 10.85; H, 0.9; C1, 24.05; N, 6.3%; M , 8851. From sodium bromoiridate (0.39 g.) and 1 , 2-dithiocyanatoethane (0.09 g.) was prepared similarly the brorno-complex (0.28 g.) (Found: C, 8-3; H, 0-6; Br, 41.85; N, 4.9. C,H,Br,Ir,N,S, requires C, 8.35; H, 0.7; Br, 41.65; N, 4.85%).

iridium(II1) .-The chloro-complex (0- 1 g.) and sodium iodide (0.3 g.) were refluxed in methyl ethyl ketone (25 ml.) for 12 hr. The complex (0.15 g.) was filtered off and purified as above (Found: C, 6.6; H, 0-7; I, 52.9; N, 3-85. C,H,I,Ir,N,S, requires C, 6-7; H, 0.55; I, 53-15; N, 3.9%).

Trichlovo- ( 1,2-dithiocyanatoethane) -p-tohidineiridium (111).

-Di-p-chlorotetrachlorobis- ( 1 , 2-dithiocyanatoethane) di- iridium(II1) (0.1 g.) and p-toluidine (0.1 g.) were refluxed in methyl ethyl ketone (20 ml.) for 6 hr. The complex (0.1 g . ) , m. p. >250", was filtered off, washed with ether, and dried at 110" for 3 hr. (Found: C, 24.0; H, 2.45; C1, 19.1; N, 7.65. Cl,H,,C1,IrN,S, requires C, 23.95; H, 2.35; C1, 19-3; N, 7.6%). Similarly prepared was trichloro-( 1,2-di- thiocyanatoetha?ze)pyridineiridiu~(III), m. p. > 250" (Found : C, 20.5; H, 1-65; C1, 20.25; N, 8-0. C,H,CI,IrN,S, requires C, 20.7; H, 1-7; CI, 20.4; N, 8 .05~o) .

Physical Measurements.-Infrared spectra were recorded on a Grubb-Parsons double-beam spectrophotometer GS4, both in potassium bromide discs and in Nujol mulls. Solid reflectance spectra were recorded on an S.P. 500 spectrophotometer fitted with diff use-reflection attachment S.P. 540. Magnetic measurements were carried out using a Gouy balance.

A nalaysis.-The cobalt complexes were decomposed by heating with a 1 : 1 mixture of concentrated nitric acid and S30/, perchloric acid for 4 hr. This solution was then heated to fuming, and the residue extracted with water. The metal was determined gravimetrically as tetrapyridine cobalt dithiocyanate. Carbon, hydrogen, bromine, chlorine, iodine, and nitrogen were determined by Mr. A. Hedley of this Department.

I thank Professor H. M. N. H. Irving for his interest and encouragement, and acknowledge the award of the Brother- ton Research Lectureship of the University of Leeds which made this research possible.

[6/956 Received, July 27th, 19661

4.45%).

Di-El.-cJzlorotetraclilol.obis- (1,2-dithiocyanatoethane)di-

Di-p-iodotetraiodobis- ( 1,2-dithiocyanatoethane) di-

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