Synthesis, properties and the reactivity of 2,2'-diselenazole-bridged dinuclear selenium species (Se(2)-Y-Se(2))-mediated by Se(0) and Se(2)(+) salts. Herein, the first examples of 2,2'-diselenazole-bridged dinuclear selenium species (Se(2)-Y-Se(2)) have been prepared via the reaction of selenium oxide and sulfur with diphenyl diselenide, where Y is a donor solvent molecule. The compounds have been characterized by 1 H and (77) Se NMR, UV-visible absorption, FTIR, mass spectrometry and X-ray crystallography. Their redox activity has been studied by cyclic voltammetry using Bu(4)NClO(4) as a supporting electrolyte. The electrochemical results show that these molecules possess a reversible redox process over a wide potential window (from 0.01 to 2.0 V vs FcH/FcH(+)). Notably, in the presence of Bu(4)NClO(4), they are much more active toward the oxygen reduction reaction than the uncoordinated diphenyl diselenide, while the activity is much lower in tetrahydrofuran. The oxidation product has been isolated, characterized and assigned as a diselenide. These results reveal a higher electrochemical and electrocatalytic activity for the reactions involving Se(2)-Y-Se(2) in the presence of the supporting electrolyte compared with that in the absence of the electrolyte, and they provide a novel way for developing new and better electrocatalysts for oxidation reactions.