Electrochemical and Photophysical Properties of New Triazole-Bridged Heterobimetallic Ruthenium-Rhodium and Ruthenium-Iridium Complexes

The synthesis, characterization, and the electrochemical and photophysical properties of [(bpy)2RuII(bpt)RhIII(ppy)2]2+, [(bpy)2RuII, (bpt)IrIII(ppy)2]2+, {[RhIII(ppy)2]2(bpt)}+, and {[IrIII(ppy)2]2(bpt)}+are reported (Hppy = 2-phenylpyridine; bpy = 2, 2'-bipyridine, Hbpt = 3, 5-bis(pyridin-2-yl)-l, 2, 4-triazole). The Ru(bpy)2moiety is bound via N1 of the triazole ring, while the M(ppy)2center (M = Rh or Ir) is coordinated via the N4 of the triazole ring. The electrochemical measurements show that in the mixed-metal complexes the first oxidized metal is Ru and the first reduced ligand is bpy. The homobimetallic Ir and Rh complexes exhibit a bpf-based reduction. The absorption spectra of the mixed-metal complexes exhibit both Ru → bpy and M → ppy transitions. The energies of these transitions are different from those of the their homobimetallic analogs. The emission observed for {[Rh(ppy)2]2- (bpt)}+at 77 K corresponds to a ligand-centered excited state, while for the analogous iridium complex a chargetransfer emission, which involves the bpt- ligand, is observed. In the mixed-metal complexes efficient energy transfer occurs from higher energy excited states centered on the M(ppy)2 component to the lowest energy excited state, which is a metal-to-ligand charge transfer level localized on the Ru(bpy)2component.