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Some mercaptides and mercaptide complexes of nickel and palladium
J. Inorg. Nucl. Chem., 196-1,Vol. 26, pp. 807 to 810. PergamonPress Ltd. Printed in Northern Ireland
SOME MERCAPTIDES A N D MERCAPTIDE COMPLEXES OF NICKEL A N D PALLADIUM R. G. HAYTER and F. S. HUMIEC The Mellon~nstitute, 4400 Fifth Avenue, Pittsburgh 13, Pa.
(Received 17 September 1963) Abstract--Two methods for the preparation of nickel mercaptide complexes of the type [Ni(SC6Hs)2L2] (L (C~Hs)sP, C6Hs(CH3)2P and L2 ~ (CnHn)2PCH2CHzP(CsHs)2) are described. The complexes are square planar and dissociate readily in solution. Analogous palladium complexes are reported and the structures of the palladium mercaptides, [Pd(SR)~],, discussed.
DURING a study of the structure of some tertiary phosphine complexes of nickel halides, ~1) it was observed that no analogous complexes of the nickel mercaptides appear to have been reported. We have therefore attempted to prepare some representative complexes of the type [Ni(SR)2L2] (R = C2H5, C6H5; L = tertiary phosphine ligand). Since the parent nickel mercaptides ~2) are polymeric insoluble compounds, which do not react with most ligands under normal conditions, we have used two preparative methods starting from tertiary phosphine complexes of nickel(lI) or nickel(0) respectively. These are summarized in Equations (1) and (2) below. [NiC12L~] + 2RSNa--,- [Ni(SR)zL2] ÷ 2NaC1 [Ni(CO)2L2] + R2S2 --,- [Ni(SR)2L2] + 2CO
(l) (2)
The method involving nickel(0) complexes (Equation 2) has been used only to prepare [Ni(SC6Hs)2{(C6Hs)~PCHzCHzP(C6Hs)z}], although there is reason to believe that this method can be extended to other ligands and to other metals. In the course of this work, we also prepared, for comparison purposes, some of the corresponding complexes of palladium (II), and have re-examined the properties of the palladium mercaptides3 3) EXPERIMENTAL Microanalyses and molecular weight determinations were by Schwarzkopf Microanalytical Laboratories. Melting points were determined on a Kofler hot stage and are corrected. Infra-red spectra were measured on a Beckmann IR-4 spectrophotometer and spectra in the range 280-1000 m/z on a Carey 14 spectrophotometer, the method of Shibata being used for the solid state measurements. 14~ Preparation of Complexes. All preparations were carried out in a nitrogen atmosphere. The nickel and palladium dichloro complexes were prepared by addition of the calculated quantity of the phosphine ligand to concentrated solutions of NiCI~'6H20 and Na2PdCl4 respectively in ethanol. The precipitated nickel complexes were filtered off, dried and used without further purification; the palladium complexes were crystallized before use. [Ni(CO)2{(C6H~)~PCH2CHzP(C~H~)2}] was prepared as previously described/~ 11~R. G. ]-IAYTERand F. S. HUMIEC,J. Amer. Chem. Soc. 84, 2004 (1962). 121 K. A. JENSEN,Z. Anorff. Chem. 252, 227 (1944). (a~ F. G. MANN and D. PURDIE, J. Chem. Soe. 1549 (1935). c4~ G. MAKI, J, Chem. Phys. 29, 162 (1958). 15~ j. CHATT and F. A. HART, J. Chem. Soc. 1378 0960). 807
808
R . G . HAYTER and F. S. HUMmC
The nickel mercaptide complexes (except the chelate derivative) tend to dissociate in solution and recrystallizations were therefore best carried out in the presence of small amounts (ca. 10 per cent) of free phosphine ligand. Di(phenylthio)bis(triethylphosphine)nickel (113. [NiCI,(P(C,Hs)8}~] (1.00 g, 2-73 mmoles) in benzene (20 ml) was treated with CsHsSNa (5.66 mmoles, 9.46 ml of a 0"58 N ethanolic solution) to give an intense red solution. After removal of solvent at 15 ram, the brown residue was crystallized from n-hexane to give the pure complex as brown-red rhombs (m.p., 275-290 °, decomp.; yield, 5 per cent). (Found: C, 55"9; H, 7'7; S, 12"7. Calc. for C~4H40NiP2S~: C, 5615; H, 7.85; S, 12"5~o). The solid state spectrum shows maxima at 580, 462, 368, 320 (sh) alld 290 m#. Di(phenylthio)bis(phenyldimethylphosphine)nickel (I1). This cot~lpound was similarly prepared and crystallized from chioroform-hexane mixture to give large dark red crystals (m.p., 135-149 °, decomp.; yield, 20 per cent). (Found: C, 60.3, 60"1; H, 5.7, 5'7; Ni, 10.75; S, 12'0. Calc. for C~sHzsNiP2S~: C, 59.7; H, 5"0; Ni, 11.2; S, 12.3~). The solid state spectrum shows maxima at 550 (sh), 498 and 400 (sh) ml~. Similar attempts to prepare [Ni(SCrHs)2{P(C~H~)8},] and [Ni(SCeHs)~{P(C,Hs)(CsHs)~}~] gave red solid products which rapidly decomposed into insoluble [Ni(SCsHs)2]~ on attempted crystallization. Attempts were also made to synthesize ethylthio complexes (R = C2H5), but the crude products decomposed during purification. Di(phenylthio)(l :2bis(diphenylphosphino)ethane)nickel (113. [Ni(CO),{(CeHb),PC,H,P(CeHs),}] (1"29 g, 2"52 mmoles) and (C6H5)2S2 (0.56 g, 2.52 mmoles) were refluxed together in benzene (20 ml) for 3 hr to give a dark red solution. The solution was then filtered, diluted with hexane (40 ml) and cooled to give red crystals. Recrystallization from ethanol gave dark red needles (m.p., 250--60° decomp.; yield, 21 per cent). (Found: C, 67.7; H, 5"1; Ni, 8.8; S, 9.7. tool. wt. (CH,Br,), 648. Calc. for C38H34NiP2Ss: C, 67"6; H, 5.1 ; Ni, 8"7; S, 9.5 ~ mol. wt., 675.5). The solid state spectrum shows maxima at 527, 380 (sh), 335 (sh) and 300 m/*. This compound was also prepared in 80 per cent yield from [NiCI~((CrHs)2PC2H4P(C~Hs)~}]and CrHsSNa in ethanol. The identity of the compounds were established by comparison of their melting points and X-ray powder patterns. The reactions of nickel carbonyl with disulphides. Ni(CO)4 (4"0 ml., 5"3 g, 31-0 mmoles) and (CeHs)~S2 (3.4 g, 15.5 mmoles) were heated together in benzene solution for 1 hr. An intense red solution was first obtained, with subsequent precipitation of dark brown [Ni(SCsHs)z]~. After filtration, the product was well washed with benzene and hexane (yield, 35 per cent). (Found: C, 51.55; H, 3.65; Ni, 20.4; S, 22.3. Calc. for C12H10NiS2: C, 52.0; H, 3-6; Ni, 21.2; S, 23.15 ~). Nickel carbonyl reacts similarly with dimethyl disulphide in boiling hexane to give [Ni(SCH,)z],, as a very dark brown precipitate (yield, 30 per cent). (Found: C, 16.4; H, 3.9. Calc. for C2HeNiS2: C, 15.7; H, 4'0~o). The infra-red spectra of the nickel mercaptides (Nujol mulls) show no absorption due to carbonyl stretching vibrations in the range 1700-2200 cm -1. Di(phenylthio)bis(triethylphosphine)palladium (113.* [PdC12{P(C2Hs)~}~] (0"50 g, 1"21 mmoles) in ethanol (15 ml) was added to a solution of CoH~SNa (2.42 mmoles) in ethanol (5 ml) to give an orange-red solution, which deposited first a white solid and then yellow needles. After washing with water and ethanol, the precipitated product was crystallized from ethanol to gwe golden-yellow needles (m.p. 134--40°; yield, 84 per cent). (Found: C, 51.25; H, 7.55; P, 11"0. tool. wt. (CoHo), 540. Calc. for C~H~0P~PdSs: C, 51.4; H, 7.2; P, 11.0~). Di(phenylthio)(l:2bis(diphenylphosphino)ethane)palladium (113. This compound was similarly prepared and crystallized from a large volume of ethanol to give orange needles (m.p., 210-215 °, decomp.; yield, 60 per cent). (Found: C, 63.5; H, 5-0. Calc. for Cs,Hs~P~PdS~: C, 63.1 ; H, 4.7 ~). Di(ethylthio)(1:2bis(diphenylphosphino)ethane)palladium (113. This compound was also similarly prepared and crystallized from ethanol as orange rods (m.p. 186--193°, decomp,; yield, 89 per cent). (Found: C, 57-7, 57.6; H, 5'6, 5"6 tool. wt. (CHCla), 614. Calc. for Ca0Ha~PzPdSa: C, 57"5; H, 5"5 ~o. mol. wt., 627). The palladium mercaptides, [Pd(SR)z]~ (R = Et, n-CsH~, i-C8I-I~)were prepared as previously described from Na~PdCI~ and the corresponding thiol,s The iso-propyl derivative is new and was * Previously prepared ~ by reaction between C~H~SH and [Pd(CH~)2(P(C~H~)s}d. ~ G. CALVINand G. E. COATES,J. Chem. Soc. 2008 (1960).
Some mercaptides and mercaptide complexes of nickel and palladium
809
crystallized from benzene-hexane as orange micro-needles, which decompose above 280°. (Found: C, 27.8, 27.8; H, 5.6, 5.65 mol. wt. (C6H~), 1632. Calc. for CoHlaPdS2: C, 28.1 ; H, 5.5~ mol. wt. of hexamer, 1540. [Pd(Sn-C3HT)z]was crystallized from acetone, successive crops having melting points 210-230°, 243-248° and 255-259°. (Found: C, 28"3, 28'3, 27"8; H, 5"65, 5.7, 5-3; tool. wt. (CoHe), 1372 and 1208). DISCUSSION The properties of the nickel mercaptide complexes [Ni(SR)2L2] (R = C6H5) indicate that they contain four -co-ordinate square planar nickel (II). This is shown by the absence of any absorption bands in the 600-1000 mff region of the spectrum where tetrahedral complexes of the type [NiX2L2] (X = halide) show strong absorption, C7)and is confirmed by the diamagnetism of [Ni(SC6Hs)2{P(CH~)z(C6Hs)}2 ]. This result is not entirely unexpected since the nickel mercaptides themselves are also diamagnetid zl and hence contain square planar nickel. The spin-paired square planar structure of these compounds may be due, at least in part, to the strong ligand field exerted by the sulphide ligands. The preparation of [Ni(SC6Hs)2{(C6Hs)2PCH2CHzP(C6Hs)2}] according to Equation (2) involves oxidation of nickel from the zero to the bivalent state with corresponding reduction of the disulphide to the mercaptide anion. This reaction is similar to the cleavage of disulphides which occurs on reaction with metal carbonyls to give sulphur bridged complexesJ s~ In this connection it is interesting that Ni(CO)4 reacts with RzS~(R = CHa, Cell5) with loss of all its carbonyl groups to give [Ni(SR)z],*. There was some indication of the formation of a dark red intermediate complex, but only the nickel mereaptides were isolated. Structure o f the palladium mercaptides. JENSEN first suggested that the nickel mercaptides were linear polymers based on square planar nickel (II) and their properties, particularly diamagnetism and insolubility appear to be consistent with this R
Ni
R
Ni ,~. / / "S R
R
/s,.
/ s\ Ni "~\
S /
R
R
I
structure (I). 12) It has been proposed that the palladium mercaptides have also linear polymeric structuresJ z) The insoluble nature of the ethyl and phenyl derivatives are consistent with this, but the n-propyl and higher members are soluble in organic solvents and can be crystallized. X-ray crystallographic measurements on single crystals of the n-propyl compound showed that the triclinic unit cell contained six monomer unitsJ z~ The space group could be either P1 or Pi, but a negative piezoelectric testt favours the centrosymmetric space group Pi. * Mo(CO)~ undergoes a similar reaction with the disulphide, bis(trifluoromethyl)dithietene to give [Mo(S2C2(CF3)~)8].19~ t We are indebted to Dr. G. S. SMITnfor this measurement. ~7~M. C. BROWNING,J. R. MELLOR,D. J. MORGAN,S. A. J. PRATT,L. E. SUTTONand L. M. VENANZI, J. Chem. Soc. 693 (1962) and references therein. ~s~R. B. KING,J. Amer. Chem. Soc. 84, 2460 (1962) and references therein. tg~R. B. KING, lnorg. Chem. 2, 641 (1963).
810
R . G . HAY'I'ER and F. S. HUMIEC
On the basis of the data presented above, it seems possible that the higher aliphatic palladium percaptides are not linear high polymers, but form small discrete, possibly cyclic, molecules. In the case of [Pd(Sn-C3HT)~]. the X-ray data are consistent with a centrosymmetric hexamer (n = 6) in the crystalline state. The molecular weight data in solution also indicate that, in general, the soluble palladium mercaptides have values of n approaching six, the slightly lower values usually obtained probably being due to small amounts of lower polymers.
I S II
s
s Pd
Ix Two possible structures are proposed for [Pd(Sn-CaHv)2]n (II, III),* both of which are based on four-co-ordinate square planar palladium (II) and three-coordinate pyramidal sulphur. In II, the palladium atoms are at the corners of a regular octahedron and the bridging mercaptide groups lie above each edge. In III, the palladium atoms form a six-membered ring, each adjacent pair of metal atoms being joined by a double mercaptide bridge, which is folded along the SS axis. A final solution to the structure of the palladium mercaptides must await an X-ray structural determination.
Acknowledgements--The authors thank Dr. G. S. SMrr~tfor discussions concerning the crystallographic data and Dr. L. VASr.Afor the measurement of magnetic susceptibility. * In structuresII and III, the n-propyl groups attached to the sulphur atoms are omitted for clarity.
SOME MERCAPTIDES A N D MERCAPTIDE COMPLEXES OF NICKEL A N D PALLADIUM R. G. HAYTER and F. S. HUMIEC The Mellon~nstitute, 4400 Fifth Avenue, Pittsburgh 13, Pa.
(Received 17 September 1963) Abstract--Two methods for the preparation of nickel mercaptide complexes of the type [Ni(SC6Hs)2L2] (L (C~Hs)sP, C6Hs(CH3)2P and L2 ~ (CnHn)2PCH2CHzP(CsHs)2) are described. The complexes are square planar and dissociate readily in solution. Analogous palladium complexes are reported and the structures of the palladium mercaptides, [Pd(SR)~],, discussed.
DURING a study of the structure of some tertiary phosphine complexes of nickel halides, ~1) it was observed that no analogous complexes of the nickel mercaptides appear to have been reported. We have therefore attempted to prepare some representative complexes of the type [Ni(SR)2L2] (R = C2H5, C6H5; L = tertiary phosphine ligand). Since the parent nickel mercaptides ~2) are polymeric insoluble compounds, which do not react with most ligands under normal conditions, we have used two preparative methods starting from tertiary phosphine complexes of nickel(lI) or nickel(0) respectively. These are summarized in Equations (1) and (2) below. [NiC12L~] + 2RSNa--,- [Ni(SR)zL2] ÷ 2NaC1 [Ni(CO)2L2] + R2S2 --,- [Ni(SR)2L2] + 2CO
(l) (2)
The method involving nickel(0) complexes (Equation 2) has been used only to prepare [Ni(SC6Hs)2{(C6Hs)~PCHzCHzP(C6Hs)z}], although there is reason to believe that this method can be extended to other ligands and to other metals. In the course of this work, we also prepared, for comparison purposes, some of the corresponding complexes of palladium (II), and have re-examined the properties of the palladium mercaptides3 3) EXPERIMENTAL Microanalyses and molecular weight determinations were by Schwarzkopf Microanalytical Laboratories. Melting points were determined on a Kofler hot stage and are corrected. Infra-red spectra were measured on a Beckmann IR-4 spectrophotometer and spectra in the range 280-1000 m/z on a Carey 14 spectrophotometer, the method of Shibata being used for the solid state measurements. 14~ Preparation of Complexes. All preparations were carried out in a nitrogen atmosphere. The nickel and palladium dichloro complexes were prepared by addition of the calculated quantity of the phosphine ligand to concentrated solutions of NiCI~'6H20 and Na2PdCl4 respectively in ethanol. The precipitated nickel complexes were filtered off, dried and used without further purification; the palladium complexes were crystallized before use. [Ni(CO)2{(C6H~)~PCH2CHzP(C~H~)2}] was prepared as previously described/~ 11~R. G. ]-IAYTERand F. S. HUMIEC,J. Amer. Chem. Soc. 84, 2004 (1962). 121 K. A. JENSEN,Z. Anorff. Chem. 252, 227 (1944). (a~ F. G. MANN and D. PURDIE, J. Chem. Soe. 1549 (1935). c4~ G. MAKI, J, Chem. Phys. 29, 162 (1958). 15~ j. CHATT and F. A. HART, J. Chem. Soc. 1378 0960). 807
808
R . G . HAYTER and F. S. HUMmC
The nickel mercaptide complexes (except the chelate derivative) tend to dissociate in solution and recrystallizations were therefore best carried out in the presence of small amounts (ca. 10 per cent) of free phosphine ligand. Di(phenylthio)bis(triethylphosphine)nickel (113. [NiCI,(P(C,Hs)8}~] (1.00 g, 2-73 mmoles) in benzene (20 ml) was treated with CsHsSNa (5.66 mmoles, 9.46 ml of a 0"58 N ethanolic solution) to give an intense red solution. After removal of solvent at 15 ram, the brown residue was crystallized from n-hexane to give the pure complex as brown-red rhombs (m.p., 275-290 °, decomp.; yield, 5 per cent). (Found: C, 55"9; H, 7'7; S, 12"7. Calc. for C~4H40NiP2S~: C, 5615; H, 7.85; S, 12"5~o). The solid state spectrum shows maxima at 580, 462, 368, 320 (sh) alld 290 m#. Di(phenylthio)bis(phenyldimethylphosphine)nickel (I1). This cot~lpound was similarly prepared and crystallized from chioroform-hexane mixture to give large dark red crystals (m.p., 135-149 °, decomp.; yield, 20 per cent). (Found: C, 60.3, 60"1; H, 5.7, 5'7; Ni, 10.75; S, 12'0. Calc. for C~sHzsNiP2S~: C, 59.7; H, 5"0; Ni, 11.2; S, 12.3~). The solid state spectrum shows maxima at 550 (sh), 498 and 400 (sh) ml~. Similar attempts to prepare [Ni(SCrHs)2{P(C~H~)8},] and [Ni(SCeHs)~{P(C,Hs)(CsHs)~}~] gave red solid products which rapidly decomposed into insoluble [Ni(SCsHs)2]~ on attempted crystallization. Attempts were also made to synthesize ethylthio complexes (R = C2H5), but the crude products decomposed during purification. Di(phenylthio)(l :2bis(diphenylphosphino)ethane)nickel (113. [Ni(CO),{(CeHb),PC,H,P(CeHs),}] (1"29 g, 2"52 mmoles) and (C6H5)2S2 (0.56 g, 2.52 mmoles) were refluxed together in benzene (20 ml) for 3 hr to give a dark red solution. The solution was then filtered, diluted with hexane (40 ml) and cooled to give red crystals. Recrystallization from ethanol gave dark red needles (m.p., 250--60° decomp.; yield, 21 per cent). (Found: C, 67.7; H, 5"1; Ni, 8.8; S, 9.7. tool. wt. (CH,Br,), 648. Calc. for C38H34NiP2Ss: C, 67"6; H, 5.1 ; Ni, 8"7; S, 9.5 ~ mol. wt., 675.5). The solid state spectrum shows maxima at 527, 380 (sh), 335 (sh) and 300 m/*. This compound was also prepared in 80 per cent yield from [NiCI~((CrHs)2PC2H4P(C~Hs)~}]and CrHsSNa in ethanol. The identity of the compounds were established by comparison of their melting points and X-ray powder patterns. The reactions of nickel carbonyl with disulphides. Ni(CO)4 (4"0 ml., 5"3 g, 31-0 mmoles) and (CeHs)~S2 (3.4 g, 15.5 mmoles) were heated together in benzene solution for 1 hr. An intense red solution was first obtained, with subsequent precipitation of dark brown [Ni(SCsHs)z]~. After filtration, the product was well washed with benzene and hexane (yield, 35 per cent). (Found: C, 51.55; H, 3.65; Ni, 20.4; S, 22.3. Calc. for C12H10NiS2: C, 52.0; H, 3-6; Ni, 21.2; S, 23.15 ~). Nickel carbonyl reacts similarly with dimethyl disulphide in boiling hexane to give [Ni(SCH,)z],, as a very dark brown precipitate (yield, 30 per cent). (Found: C, 16.4; H, 3.9. Calc. for C2HeNiS2: C, 15.7; H, 4'0~o). The infra-red spectra of the nickel mercaptides (Nujol mulls) show no absorption due to carbonyl stretching vibrations in the range 1700-2200 cm -1. Di(phenylthio)bis(triethylphosphine)palladium (113.* [PdC12{P(C2Hs)~}~] (0"50 g, 1"21 mmoles) in ethanol (15 ml) was added to a solution of CoH~SNa (2.42 mmoles) in ethanol (5 ml) to give an orange-red solution, which deposited first a white solid and then yellow needles. After washing with water and ethanol, the precipitated product was crystallized from ethanol to gwe golden-yellow needles (m.p. 134--40°; yield, 84 per cent). (Found: C, 51.25; H, 7.55; P, 11"0. tool. wt. (CoHo), 540. Calc. for C~H~0P~PdSs: C, 51.4; H, 7.2; P, 11.0~). Di(phenylthio)(l:2bis(diphenylphosphino)ethane)palladium (113. This compound was similarly prepared and crystallized from a large volume of ethanol to give orange needles (m.p., 210-215 °, decomp.; yield, 60 per cent). (Found: C, 63.5; H, 5-0. Calc. for Cs,Hs~P~PdS~: C, 63.1 ; H, 4.7 ~). Di(ethylthio)(1:2bis(diphenylphosphino)ethane)palladium (113. This compound was also similarly prepared and crystallized from ethanol as orange rods (m.p. 186--193°, decomp,; yield, 89 per cent). (Found: C, 57-7, 57.6; H, 5'6, 5"6 tool. wt. (CHCla), 614. Calc. for Ca0Ha~PzPdSa: C, 57"5; H, 5"5 ~o. mol. wt., 627). The palladium mercaptides, [Pd(SR)z]~ (R = Et, n-CsH~, i-C8I-I~)were prepared as previously described from Na~PdCI~ and the corresponding thiol,s The iso-propyl derivative is new and was * Previously prepared ~ by reaction between C~H~SH and [Pd(CH~)2(P(C~H~)s}d. ~ G. CALVINand G. E. COATES,J. Chem. Soc. 2008 (1960).
Some mercaptides and mercaptide complexes of nickel and palladium
809
crystallized from benzene-hexane as orange micro-needles, which decompose above 280°. (Found: C, 27.8, 27.8; H, 5.6, 5.65 mol. wt. (C6H~), 1632. Calc. for CoHlaPdS2: C, 28.1 ; H, 5.5~ mol. wt. of hexamer, 1540. [Pd(Sn-C3HT)z]was crystallized from acetone, successive crops having melting points 210-230°, 243-248° and 255-259°. (Found: C, 28"3, 28'3, 27"8; H, 5"65, 5.7, 5-3; tool. wt. (CoHe), 1372 and 1208). DISCUSSION The properties of the nickel mercaptide complexes [Ni(SR)2L2] (R = C6H5) indicate that they contain four -co-ordinate square planar nickel (II). This is shown by the absence of any absorption bands in the 600-1000 mff region of the spectrum where tetrahedral complexes of the type [NiX2L2] (X = halide) show strong absorption, C7)and is confirmed by the diamagnetism of [Ni(SC6Hs)2{P(CH~)z(C6Hs)}2 ]. This result is not entirely unexpected since the nickel mercaptides themselves are also diamagnetid zl and hence contain square planar nickel. The spin-paired square planar structure of these compounds may be due, at least in part, to the strong ligand field exerted by the sulphide ligands. The preparation of [Ni(SC6Hs)2{(C6Hs)2PCH2CHzP(C6Hs)2}] according to Equation (2) involves oxidation of nickel from the zero to the bivalent state with corresponding reduction of the disulphide to the mercaptide anion. This reaction is similar to the cleavage of disulphides which occurs on reaction with metal carbonyls to give sulphur bridged complexesJ s~ In this connection it is interesting that Ni(CO)4 reacts with RzS~(R = CHa, Cell5) with loss of all its carbonyl groups to give [Ni(SR)z],*. There was some indication of the formation of a dark red intermediate complex, but only the nickel mereaptides were isolated. Structure o f the palladium mercaptides. JENSEN first suggested that the nickel mercaptides were linear polymers based on square planar nickel (II) and their properties, particularly diamagnetism and insolubility appear to be consistent with this R
Ni
R
Ni ,~. / / "S R
R
/s,.
/ s\ Ni "~\
S /
R
R
I
structure (I). 12) It has been proposed that the palladium mercaptides have also linear polymeric structuresJ z) The insoluble nature of the ethyl and phenyl derivatives are consistent with this, but the n-propyl and higher members are soluble in organic solvents and can be crystallized. X-ray crystallographic measurements on single crystals of the n-propyl compound showed that the triclinic unit cell contained six monomer unitsJ z~ The space group could be either P1 or Pi, but a negative piezoelectric testt favours the centrosymmetric space group Pi. * Mo(CO)~ undergoes a similar reaction with the disulphide, bis(trifluoromethyl)dithietene to give [Mo(S2C2(CF3)~)8].19~ t We are indebted to Dr. G. S. SMITnfor this measurement. ~7~M. C. BROWNING,J. R. MELLOR,D. J. MORGAN,S. A. J. PRATT,L. E. SUTTONand L. M. VENANZI, J. Chem. Soc. 693 (1962) and references therein. ~s~R. B. KING,J. Amer. Chem. Soc. 84, 2460 (1962) and references therein. tg~R. B. KING, lnorg. Chem. 2, 641 (1963).
810
R . G . HAY'I'ER and F. S. HUMIEC
On the basis of the data presented above, it seems possible that the higher aliphatic palladium percaptides are not linear high polymers, but form small discrete, possibly cyclic, molecules. In the case of [Pd(Sn-C3HT)~]. the X-ray data are consistent with a centrosymmetric hexamer (n = 6) in the crystalline state. The molecular weight data in solution also indicate that, in general, the soluble palladium mercaptides have values of n approaching six, the slightly lower values usually obtained probably being due to small amounts of lower polymers.
I S II
s
s Pd
Ix Two possible structures are proposed for [Pd(Sn-CaHv)2]n (II, III),* both of which are based on four-co-ordinate square planar palladium (II) and three-coordinate pyramidal sulphur. In II, the palladium atoms are at the corners of a regular octahedron and the bridging mercaptide groups lie above each edge. In III, the palladium atoms form a six-membered ring, each adjacent pair of metal atoms being joined by a double mercaptide bridge, which is folded along the SS axis. A final solution to the structure of the palladium mercaptides must await an X-ray structural determination.
Acknowledgements--The authors thank Dr. G. S. SMrr~tfor discussions concerning the crystallographic data and Dr. L. VASr.Afor the measurement of magnetic susceptibility. * In structuresII and III, the n-propyl groups attached to the sulphur atoms are omitted for clarity.