Preparation, Purification, and Characterization of Binuclear Ruthenium(II) Complexes: Bridging Ligands Based on Diazafluorenes.

A series of bimetallic complexes of ruthenium(II) bridged by heterocyclic ligands formed by the condensation of 4,5-diazafluoren-9-one with various diamines, hydrazine, 1,4-phenylenediamine, benzidine, and 4,4‘-methylenedianiline, results in metal centers separated by various distances. The complexes give rise to metal-to-ligand charge-transfer absorptions in the 450 nm region of the visible spectrum and intraligand π → π* transitions in the 300 nm region of the ultraviolet spectrum. The ruthenium(II) centers are oxidized in two closely spaced one-electron processes at potentials more positive than that for Ru(bpy)32+. The bridging ligands are reduced by two closely spaced one-electron processes at more positive potentials than that for reduction of the coordinated bipyridine ligands (∼−1.30 V), although the diazafluoreneN−Ndiazafluorene bridging ligand is reduced reversibly in two single-electron steps at E1/2 values of −0.29 and −0.52 V. After purification by eluting the “pure” complexes over a silica g...