Mixed valency in hydrogen bonded 'dimers of dimers'.

Dimolybdenum quadruply bonded compounds containing a pendant lactam functional group form self-complementary hydrogen bonded 'dimers of dimers' in the solid-state and CH(2)Cl(2) solutions. Electrochemical studies in CH(2)Cl(2) show two consecutive one-electron redox processes corresponding to oxidation of the Mo(2)(4+) cores. Spectroelectrochemical studies on the 'dimers of dimers' show no evidence of intervalence charge transfer bands in the mixed valence radical cations formed by one-electron oxidation, indicating that they are examples of proton-coupled mixed valency.