Synthesis, properties and structures of the two “electron rich” cobalt-sulphur clusters [Co 6(μ 3-S) 8(PEt 3) 6] 1+,0

Abstract

The reaction of hydrogen sulphide with [Co(H 2O) 6](BF 4) 2 and triethylphosphine in the presence of sodium tetraphenylborate or tetrabutylammonium hexafluorophosphate gave the paramagnetic clusters [Co 6(μ 3-S) 8(PEt 3) 6]( Y) ( Y = BPh 4, ( 1), PF 6, ( 2)). These compounds can be easily reduced by sodium napthalenide to the diamagnetic species [Co 6(μ 3-S) 8(PEt 3) 6] · 2C 4H 8O ( 3). The molecular structures of 1 and 3 have been established by single-crystal X-ray diffraction methods. Crystal data: ( 1) space group P 1 , a = 19.481(9), b = 15.562(7), c = 12.390(b) Å, α = 92.70(8), β = 94.50(7), γ = 94.10(9)°, Z = 2, ( 3) space group R 3 , a = 11.780(6) Å, α = 92.50(7)°, Z = 1. Both structures were solved by the heavy atom method and refined by full-matrix least-squares techniques to the conventional R factors values of 0.050 for 1 and 0.044 for 3 on the basis of 4251 and 1918 observed reflections, respectively. The two clusters [Co 6(μ 3-S) 8)(PEt 3) 6] 1+,0 are isostructural, the inner core consisting of an octahedron of cobalt atoms with all the faces symmetrically capped by triply bridging sulphur atoms. Each metal centre is additionally linked to a triethylphosphine group so that each cobalt atom is co-ordinated by four sulphur atoms and one phosphorus in a distorted square pyramidal environment. The addition of one electron whilst leaving unchanged the geometry of the inner framework, induces small changes in the structural parameters, the average CoCo and CoP distances being 2.794 (3) and 2.162 (2) Å for 1 and 2.817 (3) and 2.138 (2) Å for 3 respectively. Electrochemistry in non-aqueous solvents shows the electron-transfer sequence ▪ The tricationic species is stable only in the short time of cyclic voltammetric tests.