Mixed valence complexes involving MM quadruple bonds (M=Mo or W)

Abstract

The MM quadruple bond of configuration MM σ ² π ⁴ δ ² is redox active and in many ways ideally suited for studies of mixed valency when two or more such centres are linked by a bridging ligand. In this account, the mechanism of electronic coupling is examined for complexes of the type [L ₃ M ₂ bridgeM ₂ L ₃ ] ^0/+ where L, a pivalate; bridge, a dicarboxylate or related ligand and M, Mo or W. The represented examples allow us to probe electronic factors close to the class II/III border and readily distinguish between electron and hole transfer in the superexchange mechanism. The potential for mixed valence organic radical anions mediated by the M ₂ centre is also raised and one specific example of class III behaviour is described.