Dimolybdenum quadruply bonded compounds containing a pendant lactam functional group form self-complementary hydrogen bonded 'dimers of dimers' in the solid-state and CH2Cl2 solutions. Electrochemical studies in CH2Cl2 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.