Synthesis, spectroscopic and electrochemical characterization and molecular structure of polypyridyl ruthenium complexes containing 4,4'-azobis(pyridine)

New coordination compounds of formulae: [Ru(trpy)(bpy)(4,4′-azpy)] 2+ , 1 , [Ru(tpm)(bpy)(4,4′-azpy)] 2+ , 2 , [(trpy)(bpy)Ru(4,4′-azpy)Ru(NH 3 ) 5 ] 4+ , 3 , and [(trpy)(bpy)Ru(4,4′-azpy)Ru(bpy)(trpy)] 4+ , 5 , with trpy = 2,2′:6′,2″-terpyridine, tpm = tris(1-pyrazolyl)methane), bpy = 2,2′-bipyridine and 4,4′-azpy = 4,4′-azobis(pyridine), have been synthesized as PF 6 - salts and characterized by spectroscopic and electrochemical techniques. The structure of the cation [Ru(trpy)(bpy)(4,4′-azpy)] 2+ has been determined by X-ray diffraction analysis, which reveals a trans -configuration of coordinated 4,4′-azpy and a packing structure that is based on extensive π-interactions within neighboring molecules. Upon controlled potential electrolysis of the dinuclear [Ru II ,Ru II ] complex 3 , a stable [Ru II , Ru III ] mixed-valent species, 4 , was detected. From spectral data and Gaussian deconvolution analysis of the intervalence transition in 4 , a strong electronic interaction between both ruthenium centers is disclosed ( H AB  = 550 cm −1 ), pointing to possible applications of 4,4′-azpy as a conducting bridge in “molecular wires”.