Influence of Anions on Intervalence Charge Transfer (IVCT) in Mixed-Valence Dinuclear Complexes

Spectroelectrochemical studies of the intervalence charge transfer (IVCT) characteristics of both diastereoisomeric forms of the dinuclear complex [{Ru(bpy)2}2(μ-dpi-)] n + [bpy = 2,2‘-bipyridine; dpi- = 4,5-di(2-pyridyl)imidazolate] showed that the degree of inter-metal electronic coupling (or valence delocalization) is dependent on stereochemical identity. Increasing the relative concentration of the strongly associating anion toluene-4-sulfonate in acetonitrile/[(n-C4H9)4N]{B(C6F5)4} solution differentially decreased the level of delocalization for the two diastereoisomers. In a comparative investigation of electrochemical and spectroelectrochemical techniques of the anion-induced electron localization in [{Ru(bpy)2}2(μ-dpo)]5+ [dpo = 3,4-di(2-pyridyl)-1,2,5-oxadiazole], differences were observed between the two methods in the order and extent of effects induced by a number of inorganic anions (PF6 -, BF4 -, ClO4 -). It was determined that the measure of coupling derived from electrochemical methods was less reliable than that obtained from spectral methods. Comparative electrochemical studies were undertaken on [{M(bpy)2}2(μ-BL)] n + {M = Ru, Os; BL = dpo, dpi-), which revealed substantial differences in ΔE ox (the separation between the redox potentials for the MII−MII/MIII−MII and MII−MIII/MIII−MIII couples) for the two metal centers and therefore the comproportionation constant K c, dependent on the neutral or anionic nature of the bridging ligand.