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(NH3)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 PF6- 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 [RuII,RuII] complex 3, a stable [RuII, RuIII] 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 (HAB = 550 cm-1), pointing to possible applications of 4,4′-azpy as a conducting bridge in "molecular wires". © 2008 Elsevier Ltd. All rights reserved.