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(mu-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(mu-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(mu-BL)]n+ {M=Ru, Os; BL=dpo, dpi-), which revealed substantial differences in DeltaEox (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 Kc, dependent on the neutral or anionic nature of the bridging ligand.