Metal-metal bonded Ru3+(mu -OR)(2)Ru3+ and Ru3.5+(mu -OR)(2)Ru3.5+ (R = CH3 and CH3CH2) compounds with tetrachlorocatecholate (Cl(4)Cat) have been synthesized in the corresponding alcohol, MeOH and EtOH, from a nonbridged Ru2+-Ru3+ compound, Na-3[Ru-2(Cl(4)Cat)(4)(THF)]. 3H(2)O . 7THF (1). In alcohol solvents, compound 1 is continuously oxidized by oxygen to form Ru3+(mu -OR)(2)Ru3+ and Ru3.5+(mu -OR)(2)Ru3.5+ species. The presence of a characteristic countercation leads to selective isolation of either Ru3+(mu -OR)(2)Ru3+ or Ru3.5+(mu -OR)(2)Ru3.5+ as a stable adduct species. In methanol, Ph4PCl and dibenzo-18-crown-6-ether afford Ru3+(mu -OMe)(2)Ru3+ species, [A](2)[Ru-2(Cl(4)Cat)(4)(mu -OMe)(2)Na-2(MeOH)(6)] ([A](+) = Ph4P+ (2), [Na(dibenzo-18-crown-6)(H2O)(MeOH)](+) (3)), while benzo-15-crown-5-ether provides a Ru3.5+(mu -OMe)(2)Ru3.5+ species, [Na(benzo-15-crown-5)(2)][Ru-2(Cl(4)Cat)(4)(mu -OMe)(2)Na-2(MeOH)(6)] (4). The air oxidation of 1 in a MeOH/EtOH mixed solvent (1:1 v/v) containing benzo-15-crown-5-ether provides a Ru3.5+(mu -OMe)(2)Ru3.5+ species, [Na(benzo-15-crown-5)(H2O)][Ru-2(Cl(4)Cat)(2)(mu -OMe)(2)Na-2-(EtOH)(2)(H2O)(2)(MeOH)(2)](.)(benzo-15-crown-5) (5). Similarly, the oxidation of 1 in ethanol with Ph4PCl provides a Ru3.5+(mu -OEt)(2)Ru3.5+ species, (Ph4P)[Ru-2(Cl(4)Cat)(4)(mu -OEt)(2)Na-2(EtOH)(6)] (7). A selective formation of a Ru3+(mu -Oet)(2)Ru3+ species, (Ph4P)(2)[Ru-2(Cl(4)Cat)(4)(mu -OEt)(2)Na-2(EtOH)(2)(H2O2)(2)] (6), is found in the presence of pyrazine or 2,5-dimethylpyrazine. The crystal structures of these compounds, except 2 and 7, have been determined by X-ray crystallography, and all compounds have been characterized by several spectroscopic and magnetic investigations. The longer Ru-Ru bonds are found in the Ru3+(mu -OR)(2)Ru3+ species (2.606(1) and 2.628(2) Angstrom for 3 and 6, respectively) compared with those of Ru3.5+(mu -OMe)(2)Ru3.5+ species (2.5260(6) Angstrom and 2.514(2) Angstrom for 4 and 5, respectively. These structural features and magnetic and ESR data revealed the electronic configurations of sigma (2)pi (2)delta (*2)delta (2)pi (*2) and sigma (2)pi (2)delta (*2)delta (2)pi (*1) for Ru3+(mu -OR)(2)Ru3.5+(mu -OR)(2)Ru3.5+, respectively, in which the former is diamagnetic and the latter is paramagnetic with S = 1/2 ground state. Compound 5 forms a one-dimensional chain with alternating arrangement of a Ru3.5+(mu -OMe)(2)Ru3.5+ unit and a free benzo-15-crown-5-ether molecule by intermolecular hydrogen bonds (O(H2O). . .O(crown-ether) = 2.91-3.04 Angstrom). The cyclic voltammetry in DMF affords characteristic metal-origin voltammograms; two quasi-reversible redox waves were observed. The feature of cyclic voltammograms for the Ru3+(mu -OR)(2)Ru3+ species (2,3, and 6) and the Ru3.5+(mu -OR)(2)Ru3.5+ species (4 and 7) are similar to each other, indicating that both species are electrochemically stable. The isolation of the pyrazine-trans-coordinated species, [Ph4P][Ru(Cl(4)Cat)(2)(L)(2)] (L = pyrazine (8), 2,5-dimethylpyrazine (9)), revealed the selective isolation of 6 from pyrazine-containing solution. UV-vis spectral variation by ethanolysis for 9 demonstrated the selective conversion from the pyrazine-trans-coordinated species to the Ru3+(mu -OEt)(2)Ru3+ species without an oxidation to the Ru3.5+(mu -OEt)(2)Ru3.5+ species. This result suggests the presence of equilibrium between [Ru(Cl(4)Cat)(2)(L)(2)](-) and Ru3+(mu -OEt)(2)Ru3+ species in the synthetic condition for 6.