Synthesis, electrochemistry and mixed-valence state of dinuclear tris(acetylacetonato)ruthenium(III) complexes bridged by sulfur atoms at the γ-position of acetylacetonate

Dinuclear tris(acetylacetonato)ruthenium(III) complexes bridged by one sulfur atom (1) or two sulfur atoms (2) at the γ-position of the acetylacetonate have been synthesized by the reactions of tris(acetylacetonato)ruthenium(III) with SCl2 or S2Cl2. The molecular structure of 2 has been determined by single crystal X-ray diffraction study. The cyclic voltammograms of both the dinuclear complexes exhibit two one-electron reduction waves in acetonitrile (AN), dichloromethane (DM), benzonitrile (BN), and N,N-dimethylformamide (DMF). While the complex 1 exhibited two one-electron oxidation waves in AN, DM, and BN, complex 2 showed only irreversible waves in all the solvents. The comproportionation constants (Kc) for mixed-valence states of both RuII/RuIII and RuIII/RuIV were calculated from the redox potentials of dinuclear complexes. The values of log10Kc (RuII/RuIII) (for complexes 1 and 2) and log10Kc (RuIII/RuIV) (for complex 1) were between 1.35 and 3.55. These values are not so large and hence, the complexes may be classified as class II in the Robin and Day classification. Although no relationship could be found between Kc and the dielectric constant of the solvent, there exists a correlation between donor number (DN) of the solvent and log10Kc values.