METAL-OXO PHOTOOXIDANTS - CRYSTAL-STRUCTURE, SPECTROSCOPY AND PHOTOPHYSICAL PROPERTIES OF NEUTRAL LUMINESCENT TRANS-DIOXOOSMIUM(VI) COMPLEXES WITH CYANIDE AND MESITYL LIGANDS

A series of neutral osmium(VI)-oxo complexes having mesityl (mes) and cyanide ligands have been prepared and the crystal structures of [Os-V I(py)(2)(CN)(2)(O)(2)] (py = pyridine), [Os-VI(tmen)(CN)(2)(O)(2)] (tm en = N,N,N',N'-tetramethylethylenediamine). [Os-VI(mes)(2)(phen)(O)(2) ] (phen = 1,10-phenanthroline) and [Os-VI(mes)(2)(tmen)(O)(2)] determi ned. While [Os(mes)(2)(L-L)(O)(2)] (L-L = chelating aromatic diimines and diamines) are non-emissive, the related [Os(L-L)(CN)(2)(O)(2)] com plexes have long-lived and emissive excited states in solution at room temperature. The [Os(4,4'-Me(2)bipy)(CN)(2)(O)(2)] (4,4'Me(2)bipy = 4 ,4'-dimethyl-2,2'-bipyridine) complex has a E(o)(Os-VI-Os-V) value of 1.77 V vs. normal hydrogen electrode and is capable of oxidizing alke nes to the corresponding epoxides upon irradiation with UV/VIS light a t room temperature.