Increasing transmission of electronic interaction in dinuclear unsymmetric mixed-valent ruthenium complexes

The preparation and characterization by spectroscopic and electrochemical techniques of new dinuclear complexes of the type [(tpm)(bpy)Ru^II(L)Ru^II/III(NH₃)₅]^4+/5+ (bpy = 2,2′-bipyridine), tpm = tris(1-pyrazolyl)methane, L = pz (pyrazine), 4,4′-bpy (4,4′-bipyridine), BPE (trans  -1,2-bis(4-pyridyl)ethylene) and PCA (= 4-pyridinecarboxaldehyde azine), are described in this work. The analysis of the visible spectral data for the metal-to-metal charge transfer (MMCT) bands in the corresponding mixed-valent species $[RubII,RuaIII]$ (Ru_b = Ru bonded to bpy; Ru_a = Ru bonded to NH₃) allows the determination of the reorganization energies λ   and electronic coupling elements H  _AB for the intramolecular electron transfers $RubII\to RuaIII$ mediated by L. An increased transmission of the metal-to-metal electronic interaction is disclosed for this series, when comparing the distance dependence of H_AB to that of the analogous series with trpy (2,2′:6′,2″-terpyridine) acting as a spectator ligand instead of tpm.