Luminescent nitridometal complexes. Photophysical and photochemical properties of the ³ [(d xy ) ¹ (d π* ) 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 OsN distances are 1.68(1), 1.630(7) and 1.629(8)Å respectively. In the latter two complexes the OsN 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[dxy′,dπ.] 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 µs (at infinite dilution) in degassed acetonitrile at room temperature. Based on quenching studies with aromatic hydrocarbons, this complex is a powerful photooxidant with E⊖[OsVI*–OsV] being 2.12(30)V vs. the normal hydrogen electrode.