PHOTOREDOX PROPERTIES OF [OSN(NH3)4]3+ AND MECHANISM OF FORMATION OF [(OS(NH3)4(CH3CN))2N2]5+ THROUGH A NITRIDO-COUPLING REACTION

The oxidation of [Os(NH3)5Cl]2+ by Ce(IV) in water gave [OsN(NH3)4]3+ quantitatively. Excitation of [OsN(NH3)4]3+ in the solid state or in solution at 300-400 nm resulted in room-temperature photoluminescence. The low-lying spin orbital E sublevel of the 3E {3[(d(xy))1(d(pi)*)1]} state was assigned as the emission state. The excited state of [OsN(NH3)4]3+ was quenched by electron donors such as aromatic hydrocarbons, alkoxybenzenes, amines and alcohols. A photoinduced electron-transfer mechanism is proposed for the quenching processes. The emission lifetime of [OsN(NH3)4]3+ depended on the complex concentration. An excited-state bimolecular self-quenching mechanism ([Os(VI) = N]* + [Os(VI) = N] --> product) is likely. Photolysis of [OsN(NH3)4]3+ in the presence of an electron donor such as 1,4-dimethoxybenzene or C6Me6 in acetonitrile led to the formation of the mu-dinitrogen product [{Os(NH3)4(CH3CN)}2N2]5+. The coupling reaction obeyed the kinetics rate = k2[Os(VI)][Os(V)] where k2 was estimated to be (3.75 +/- 0.30) x 10(5) dm3 mol-1 s-1 at 298 K. Oxidation of [{Os(NH3)4-(CH3CN)}2N2]5+ by Ce(IV) in water followed by precipitation with 2 mol dm-3 HCl gave the product [OsN(NH3)4]Cl3 in detectable yield.