Subnanosecond Isomerization in an Osmium−Dimethyl Sulfoxide Complex

We report the structure, spectroscopy, and electrochemistry of cis-[Os(bpy)2(DMSO)2](OTf)2, where bpy is 2,2‘-bipyridine, DMSO is dimethyl sulfoxide, and OTf is trifluoromethanesulfonate. Electrochemical measurements are consistent with S-to-O isomerization following the oxidation of Os2+ (1.8 V vs Ag/AgCl). Visible irradiation of the metal-to-ligand charge-transfer transition (355 nm) of [Os(bpy)2(DMSO)2]2+ in the solid state and solution yields an emissive S-bonded excited state and S-to-O excited-state isomerization on a subnanosecond time scale. These results and a comparison to the nonphotoactive [Os(bpy)2Cl(DMSO)]+ are discussed.