Outer Sphere Perturbation of Delocalized Mixed-Valence Complexes

The complexes [{Ru(ttp)(bpy)}2(μ-adpc)][PF6]2 and [{Ru(ttp)(bpy)}2(μ-dicyd)][PF6]2, where ttp is 4-toluene-2,2‘:6‘,2‘ ‘-terpyridine, bpy is 2,2‘-bipyridine, adpc2- is azodi(phenylcyanamide), and dicyd2- 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(μ-adpc)][PF6]2·6DMF, revealed a planar bridging adpc2- 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 C2h 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(μ-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.