HOMONUCLEAR AND HETERONUCLEAR RUTHENIUM AND OSMIUM COMPLEXES CONTAINING AN ASYMMETRIC PYRAZINE-BASED BRIDGING LIGAND

The synthesis, characterization, and electrochemical, photophysical, a nd photochemical properties of the compounds [Ru(bpy)(2)(L)](2+) (Ru), [Os(bpy)(2)(L)](2+) (Os), [(L)Os(bpy)(2)Cl](+) (OsCl), [Ru(bpy)(2)(L) Ru(bpy)(2)Cl](3+) (RuRuCl), [Os(bpy)(2)(L)Os(bpy)(2)Cl](3+) (OsOsCl), [Ru(bpy)(2)(L)Os(bpy)(2)Cl](3+) (RuOsCl), and [Os(bpy)(2)(L)Ru(bpy)(2) Cl](3+) (OsRuCl) are reported (bpy = 2,2'-bipyridine, L = 1-methyl-3-( pyrazin-2-yl)-1,2,4-triazole). The Os(bpy)(2) and the Ru(bpy)(2) moiet ies are coordinated to the pyrazyltriazole ligand in two different way s, i.e. in a bidentate fashion via the triazole ring and N1 of the pyr azine ring and in a monodentate fashion only via N4 of the pyrazine ri ng. In the homonuclear dimers the monodentate bound metal has an oxida tion potential that is approximately 400 mV lower than that of the bid entate bound metal. Spectroelectrochemical investigations suggest the presence of a weak interaction between the metal centers in the dinucl ear species. The emission properties of the compounds are indicative o f efficient energy transfer in the excited state, leading to emission from only one metal unit. In acetone both RuRuCl and the OsRuCl show p hotodissociation of the monodentate ruthenium moiety; however, RuOsCl and OsOsCl were found to be photostable.