LUMINESCENT NITRIDOMETAL COMPLEXES - PHOTOPHYSICAL AND PHOTOCHEMICAL PROPERTIES OF THE 3[(D(XY))1(D-PI-ASTERISK)1] EXCITED-STATE OF NITRIDOOSMIUM(VI) COMPLEXES WITH POLYPYRIDINE LIGANDS

Nitridoosmium(VI) complexes of substituted 2,2'-bipyridines and 1,10-phenanthrolines have been prepared from [OsNCl4]- and the appropriate chelating ligands in acetonitrile. Reaction of [Os(bipy)NCl3](bipy = 2,2'-bipyridine) and [Os(terpy)NCl2]Cl (terpy = 2,2':6',2''-terpyridine) with neat trifluoromethanesulfonic acid gave [Os(bipy)NCl2(H2O)]+ and [Os(terpy)N(Cl)(CF3SO3)]+ respectively. The crystal structures of [Os(dmbipy)NCl3](dmbipy = 5,5'-dimethyl-2,2'-bipyridine), [Os(bipy)NCl2(H2O)]+ and [Os(terpy)N(Cl)(CF3SO3)]+ show that the Os=N distances are 1.68(1), 1.630(7) and 1.629(8) angstrom respectively. In the latter two complexes the Os=N moiety is perpendicular to the plane of the chelating ligand. The spectroscopic, photophysical and photochemical properties of the newly prepared complexes have been studied. All have long-lived and emissive 3[d(xy),d(pi).] excited states in the solid state and in fluid solution at room temperature. The complex mer-[Os(terpy)NCl2][ClO4] has the longest emission lifetime 4.64 mus (at infinite dilution) in degassed acetonitrile at room temperature. Based on quenching studies with aromatic hydrocarbons, this complex is a powerful photooxidant with E THETA [Os(VI)*-Os(V)] being 2.12(30)V vs. the normal hydrogen electrode.