Structural features of (C5H5)2Mo2S6 clusters: an EHMO study

Extended Hückel molecular orbital calculations on S 6 in the planar D 6h configuration and in the bent C 2v geometry reveal that the former is favored for S 6 2+ and the latter for S 6 4− . It is shown that the additional six electrons would populate one π* and two σ* orbitals in the planar structure. In contrast, when these hexasulfur fragments are incorporated in triple-decker sandwich compounds the pseudo-D 6h structure is favored for [(C 5 H 5 )Mo(S 6 )Mo(C 5 H 5 )] 6+ but the C 2v geometry is predicted for [(C 5 H 5 )Mo(S 6 )Mo(C 5 H 5 )] 2+ which possesses only four more electrons. The required extra two electrons are shown to originate from a metallic δ-type molecular orbital. These EHMO calculations are in complete accord with some very recent experimental results from Gillespie's laboratory. Keywords: Molybdenum–sulfur clusters, EHMO calculations.