| Abstract
| - The mixed-valence dinuclear ruthenium complex [Ru2(bpmp)(μ-OAc)2]2+ (where bpmp is the phenolate anionof 2,6-bis[bis(2-pyridylmethyl) aminomethyl]-4-methylphenol, H-bpmp) has been studied by UV−Vis−NIR,IR, and EPR spectroscopic and electrochemical techniques. The Ru2II,III complex undergoes reversible one-electron reduction (E1/2 = −0.61 V vs Fc+/0) and oxidation (E1/2 = 0.09 V vs Fc+/0), resulting in the Ru2II,IIand Ru2III,III complexes, respectively. A comproportionation constant of Kc = 1.10 × 1012 (ΔGc° = −68 kJmol-1) indicates considerable stability of the mixed-valence state. The paramagnetic complex displays a rhombicEPR spectrum (g1 = 2.492; g2 = 2.242; g3 = 1.855) arising from a ground state in a S = 1/2 low spin systemin a low symmetry environment. Three intense, distinguishable intervalence bands are observed in the NIRto mid-IR spectrum of [Ru2(bpmp)(μ-OAc)2]2+ at 3765 cm-1 (ε = 1840 M-1cm-1), 5615 cm-1 (ε = 10590M-1cm-1 ), and 7735 cm-1 (ε = 3410 M-1cm-1). All intervalence bands are symmetric but more narrowthan predicted for the classical limit and independent of solvent polarity. The results of the spectroscopic andelectrochemical characterization indicate that [Ru2(bpmp)(μ-OAc)2]2+ is either electronically delocalized (classIII, Hab = 1880 cm-1) or at the borderline between localization and delocalization (class II−III, Hab ≥ 590cm-1) with rapid electron transfer (kET> 4 × 1012 s-1) decoupled from solvent reorientation but with aresidual activation barrier (Ea ≤ 440 cm-1) from inner reorganization.
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