Synthesis, Crystal Structure and Electrochemistry of μ-Acetatodi-μ-hydroxo-bis[(1,4,7-triazacyclononane)ruthenium(III)]-tris-iodide. Characterization of Some Ru(II)—Ru(III) Mixed Valence Species

Abstract

A series of mononuclear complexes of ruthenium containing the cyclic triamine ligand 1,4,7-triazacyclononane ([9]aneN3 = L; C6H15N3) have been prepared: [RuIIL (dmso)2Cl]Cl (dmso = dimethyl sulfoxide), [RuIIILX3] (X = C1- , Br-), [RuL2](PF6)2, [RuL(C2O4)I]. Hydrolyses of RuLCl3 under a variety of reaction conditions afford dinuclear species: [RuIII 2L2(μ-OH)2(μ-CH3CO2)]I3·H2O , [RuIII 2L2(μ-OH)2Cl2](PF6)2, and the mixed-valence species [Ru2L2(μ-Cl)3](PF6)2. The complex [Ru2L2(μ-OH)2(μ-CH3CO2)]I3-H2O has been characterized by a single-crystal X-ray diffraction study. The compound crystallizes in the monoclinic space group P21/c with a = 14.70(1) Å , b = 19.00(1) Å , c = 9.714(7) Å , β = 99.62(7)°, and V = 2674 Å3, dcalcd = 2.37 g cm-3 for Z = 4, and mol wt 952.3. The structure was solved by direct methods using 2519 unique reflections with I > 2σ(I). Final residuals were R1 = 0.0615 and R2 = 0.075. The structure consists of μ-hydroxo- and μ-acetato- bridged dinuclear cations and iodide anions. The observed diamagnetism and a short Ru-Ru bond distance of 2.572(3) Å are indicative of a Ru-Ru single bond. The electrochemical properties of [Ru2L2(μ-OH)2(μ-CH3CO2)]3+ and [Ru2L2(μ-Cl)3]2+ have been investigated by cyclic voltammetry, and by coulometry. Two one-electron redox processes have been identified for both complexes the first of which exhibits a reversible wave, whereas the second wave at more negative potentials is irreversible. The blue mixed valence species [Ru2L2(μ-OH)2(μ-CH3CO2)]2+ has been characterized in solution.