Outer sphere perturbation of delocalized mixed-valence complexes.

Abstract

The complexes [[Ru(ttp)(bpy)](2)(micro-adpc)][PF(6)](2) and [[Ru(ttp)(bpy)](2)(micro-dicyd)][PF(6)](2), where ttp is 4-toluene-2,2':6',2' '-terpyridine, bpy is 2,2'-bipyridine, adpc(2)(-) is azodi(phenylcyanamide), and dicyd(2)(-) is 1,4-dicyanamidebenzene, were prepared and characterized by IR and NIR, vis spectroelectrochemistry, and cyclic voltammetry. The crystal structure of the complex, [[Ru(ttp)(bpy)](2)(micro-adpc)][PF(6)](2).6DMF, revealed a planar bridging adpc(2)(-) ligand with the cyanamide groups adopting an anti configuration. IR and comproportionation data are consistent with delocalized mixed-valence complexes, and a spectroscopic analysis assuming C(2)(h) microsymmetry leads to a prediction of multiple MMCT transitions with the lowest energy transition equal to the resonance exchange integral for the mixing of ruthenium donor and acceptor orbitals with a bridging ligand orbital (the preferred superexchange pathway). The solvent dependence of the MMCT band energy that is seen for [[Ru(ttp)(bpy)](2)(micro-adpc)](3+) is due to a ground state weakening of metal-metal coupling because of solvent donor interactions with the acceptor azo group of the bridging ligand.