The isolation of novel thiolate-bridged tricopper(I,lI,I) compounds suggests that an N-donor ligand-supported Cu-I-(mu-SR)-Cu-II motif is a feasible structure to consider for the proposed mixed valence dicopper electron transfer sites in nitrous oxide reductase or cytochrome c oxidase. Two symmetry-related, three-coordinate, planar Cu(I) ions are linked via thiolate sulfur atoms to a central four-coordinate Cu(II) ion in the complexes. A localized oxidation state description is supported by the geometric features and by EPR spectroscopy.