A series of new oxo-centered triruthenium, trirhodium, and mixed diruthenium-rhodium complexes having three redox-active terminal ligands, N-methyl-4,4'-bipyridinium ion (mbpy(+)), were prepared: [Ru-3(mu(3)-O)(mu-CH3CO2)(6)(mbpy(+))(3)](PF6)(3) (1), [Ru-3(mu(3)-O)(mu-CH3CO2)(6)(mbpy(+))(3)](PF6)(4) (2), [Ru-3(mu(3)-O)(mu-C6H5CO2)(6)(mbpy(+))(3)](PF6)(ClO4)(3) (3), [Ru2Rh(mu(3)-O)(mu-CH3CO2)(6)(mbpy(+))(3)](ClO4)(4) (4), and [Rh-3(mu(3)-O)(mu-CH3CO2)(6)(mbpy(+))(3)](PF6)(4) (5) Their versatile electrochemical properties were investigated by means of cyclic voltammetry, differential-pulse voltammetry, and controlled-potential absorption spectroscopy. Ru-3 complexes 1 and 2 provide nine-step 11-electron redox waves (involving eight reversible waves) in 0.1 M (n-C4H9)(4)NPF6-CH3CN solution in the range from +2.0 to -3.0 V vs ferrocene/ferrocenium (Fc/Fc(+)) couple at 22 degrees C (M = mol dm(-3)), consisting of five Ru-3(mu(3)-O) core-based one-electron processes at +1.62, +0.64, -0.34, -1.75, and -2.76 V and the terminal ligand-based steps at -1.23, -1.37, -1.99, and -2.09 V. The two couples of terminal ligand-based processes, mbpy(+)/mbpy(.) and mbpy(.)/mbpy(-), split into two steps in 2:1 current intensity ratio. Complex 3 exhibits similar redox behavior. The Ru2Rh complex 4 exhibits eight-step 10-electron redox waves (involving six reversible waves), with the core-based redox processes at +1.65, +0.74, -0.72, and -1.88 V, mbpy(+)/mbpy(.) steps at -1.14, -1.26, and -1.45 V, and mbpy(.)/mbpy(-) steps at -2.14 V (3e). The Rh-3 complex 5 shows two-step four-electron redox behavior with a core-oxidation at +0.97 V and one-step three mbpy(+) reductions at -1.21 V (3e). The splitting of the ligand-based redox waves are caused by the ligand-ligand interactions through an empty d pi-p pi molecular orbital in the trinuclear M(3)(mu(3)-O) framework.
