Distortional isomers of a mixed-valence binuclear Cu complex

Binuclear copper complexes have important functional roles in many metalloproteins, a noteworthy example being cytochrome c oxidase, whose resting state contains a mixed-valence Cu{sub 2} site, the Cu{sub A} center. The importance of direct Cu-Cu bonding in this protein site remains unclear at this time. The work reported here demonstrates that the Cu-Cu bonding interaction in a model binuclear complex is strongly mediated by ligand environment, and the weakness of this Cu-Cu bond may have functional significance for the Cu{sub A} center.