The mixed-valence dinuclear ruthenium complex [Ru-2(bpmp)(mu-OAc)(2)](2+) (where blimp is the phenolate anion of 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 Ru-2(II,III) complex undergoes reversible one-electron reduction (E-1/2 = -0.61 V vs Fc(+/0)) and oxidation (E-1/2 = 0.09 V vs Fc(+/0)), resulting in the Ru-2(II,III) and Ru-2(III,III) complexes, respectively. A comproportionation constant of K-c = 1.10 x 10(12) (DeltaG(c)degrees = -68 kJ mol(-1)) indicates considerable stability of the mixed-valence state. The paramagnetic complex displays a rhombic EPR spectrum (g(1) = 2.492; g(2) = 2.242; g(3) = 1.855) arising from a ground state in a S = 1/2 low spin system in a low symmetry environment. Three intense, distinguishable intervalence bands are observed in the NIR to mid-IR spectrum of [Ru-2(bpmp)(mu-OAc)(2)](2+) at 3765 cm(-1) (epsilon = 1840 M(-1)cm(-1)), 5615 cm(-1) (epsilon = 10590 M-1cm-1), and 7735 cm-1 (E = 3410 M-1cm-1). All intervalence bands are symmetric but more narrow than predicted for the classical limit and independent of solvent polarity. The results of the spectroscopic and electrochemical characterization indicate that [RU2(bpmp)(mu-OAc)(2)](2+) is either electronically delocalized (class III, H-ab = 1880 cm(-1)) or at the borderline between localization and delocalization (class II-III, H-ab greater than or equal to 590 cm(-1)) with rapid electron transfer (k(ET) > 4 x 10(12) s(-1)) decoupled from solvent reorientation but with a residual activation barrier (E-a less than or equal to 440 cm(-1)) from inner reorganization.