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 gamma-position of the acetylacetonate have been synthesized by the reactions of tris(acetylacetonato)ruthenium(III) With SCl2 or S2O2. 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 (K-c) for mixed-valence states of both Ru-II/Ru-III. and Ru-III/Ru-IV were calculated from the redox potentials of dinuclear complexes, The values of log,, K, (Ru-II/Ru-III.) (for complexes I and 2) and log(10)K(c) (Ru-III/Ru-IV) (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 11 in the Robin and Day classification. Although no relationship could be found between K, and the dielectric constant of the solvent, there exists a correlation between donor number (DN) of the solvent and log, 0 K, values. (C) 2004 Elsevier B.V. All rights reserved.