A new series of oxo-centered acetate-bridged triruthenium comlexes having two redox-active N-methyl-4,4'-bipyridinium ions (mbpy(+)) have been prepared, and their reversible multistep and multielectron electrochemical properties are reported: [(Ru2RuII)-Ru-III(mu(3)-O)mu-CH3CO2)(6)(mbpy(+))(2)(CO)](2+) and [Ru-3(III)(mu(3)-O)mu-CH3CO2)(6)(mbpy(+))(2)- (L)](3+) (L = H2O, pyrazine (pz), pyridine (py), imidazole (Him), and 4-(dimethylamino)pyridine (dmap)). Among these series, the CO complex, [(Ru2RuII)-Ru-III(mu(3)-O)mu-CH3CO2)(6)(mbpy(+))(2)(CO)](ClO4)(2) . 2DMF (1b . 2DMF) was structurally characterized by X-ray crystallography. 1b . 2DMF crystallizes in the monoclinic space group P2(1)/m (No. 11) with a = 8.740(6) Angstrom, b = 32.269(6) Angstrom, c = 10.276(4) Angstrom, beta = 103.37(5)degrees, V = 2820(2) Angstrom(3), Z = 2, d(calcd) = 1.636 g cm(-3), and R = 0.071 (R(w) = 0.074) for 5277 independent reflections (\F-o\ > 3 sigma(\F-o\). The (CO)- Ru ... Ru distance (3.410(2) Angstrom) is appreciably longer than the other Ru ... Ru distance (3.276(2) Angstrom), indicating that the trinuclear core is in the valence-trapped (Ru2RuII)-Ru-III(CO) oxidation state. The cyclic voltammogram of [(Ru2RuII)-Ru-III(mu(3)-O)(mu-CH3CO2)(6)(mbpy(+))(2)(CO)](PF6)(2) (1a) shows a total of seven reversible one-electron redox steps at E(1/2) = +0.90, +0.26, -1.07, -1.17, -1.56, -1.97, and -2.32 V and one irreversible step at E(pc) = -2.99 V vs Fc/Fc(+) in a 0.1 M [(n-C4H9)(4)N]PF6-CH3CN solution (M = mol dm(-3)). All of the waves are clearly assignable to the triruthenium ''Ru-3(mu(3)-O)'' core-based or mbpy(+) ligand-based processes. The splitting of each ligand-based redox processes (mbpy(+)/mbpy(.) and mbpy(.)/mbpy(-)) into two one-electron steps indicates that electronic interactions between two terminal ligands occur through the triruthenium cluster core. Other mixed-ligand Ru-3(III) analogs also show multistep redox behavior involving a total of eight or nine electrons. While the extent of interactions between ligands is much smaller than that found in the CO complex, it is systematically changed by the nature of L; with more basic L, interactions between two mbpy(+) ligands become larger.
