Outer sphere perturbation of delocalized mixed-valence complexes

The complexes [{Ru(ttp)(bpy)}(2)(u-adpc)][PF6](2) and [{Ru(ttp)(bpy)}(2)(mu-dicyd)][PF6](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)(mu-adpc)][PF6](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-2h 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)(mu-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.