A novel Cu2N2 diamond core structure supported by an [SNS](-) ligand (1) ([SNS](-) = bis(2-tert-butylsulfanylphenyl)amido) has been prepared. This dicopper system exhibits a fully reversible one-electron redox process between a reduced (CuCu1)-Cu-1 complex, {[SNS][Cu]}(2) (2), and a class III delocalized (CUCU1.5)-C-1.5 state, [{[SNS][Cu]}(2)][B(3,5-(CF3)(2)C6H3)(4)] (3). Structural snapshots of both redox forms have been obtained to reveal remarkably little overall structural reorganization. The (CuCu)-Cu-... bond distance nonetheless undergoes an appreciable compression (similar to0.13 Angstrom) upon oxidation, providing a (CuCu)-Cu-... distance of 2.4724(4) A in the mixed-valence state that is virtually identical to the (CuCu)-Cu-... distance observed in the reduced form of the Cu-A site of thiolate-bridged cytochrome c oxidase. Despite the low structural reorganization evident between 2 and 3, the [SNS]- ligand is quite flexible. For example, square-planar geometries can prevail for divalent copper ions supported by [SNS]- as evident from the crystal structure of [SNS]CuCl (4). Physical characterization for the mixed valence complex 3 includes electrochemical, magnetic (SQUID), EPR, and optical data. The complex has also been examined by density functional methods. An attempt was made to measure the rate of electron self-exchange k(s) between the (CuCu1)-Cu-1 and the (CuCu1.5)-Cu-1.5 complexes 2 and 3 by NMR line-broadening analysis in dichloromethane solution. While the system is certainly in the fast-exchange regime, the exchange process is too fast to be accurately measured by this technique. The value for k(s) can be bracketed with a conservative lower boundary of greater than or equal to10(7) M-1 s(-1), a value that appears to be larger than other low molecular weight copper model complexes for which similar data is available. The unusually large magnitude of k(s) likely reflects the minimal structural reorganization that accompanies (CuCu1)-Cu-1 <----> (CuCu1.5)-Cu-1.5 interchange.