ELECTROCHEMICAL STUDIES OF TRIS(ACETYLACETONATO)RUTHENIUM(III) IN AMBIENT-TEMPERATURE CHLOROALUMINATE MOLTEN-SALTS

The electrochemical behavior of tris(acetytacetonato)ruthenium(III), Ru(acac)3, in a room-temperature molten salt composed of a mixture of aluminum trichloride and 1-ethyl-3-methylimidazolium chloride is studied as a function of melt composition. Ru(acaC)3 decomposes in acidic melts but is stable in neutral and basic melts, dissolving readily to give intense red solutions. The complex undergoes a Nerstian one-electron reduction process at a glassy-carbon electrode independent of the basic melt composition. The reduced Ru(acac)3- complex, depending on the melt basicity, can react with AlCl4- on the voltammetric time scale probably to form the adduct [Ru(acaC)2(acacAlCl3)]-, which gives a one-electron oxidation step at a more positive potential than that of Ru(acac)3-. When a small amount of Ru(acaC)3 is reduced by bulk electrolysis in the basic melt and allowed to stand for 1 day at room temperature, all remaining Ru(acac)3 is transformed into the colorless hexachlororuthenium(III) anion, RuCl63-. This reaction is initiated by the attack at an Ru-O bond in Ru(acac)3- by AlCl4-, followed by the breakage of the Ru-O bond. In addition, the intermediate, Ru(acac)3-nCl2n(n+1)-, generated by the rupture of an Ru-O bond, acts as a redox catalyst for the ligand replacement of Ru(acac)3 to form RuCl63-.