Luminescent nitridometal complexes. Photophysical and photochemical properties of the 3[(dxy)1(dπ*)1] excited state of nitridoosmium(VI) complexes with polypyridine ligands

Abstract

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) Å 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[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.