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]aneN 3 = L; C 6 H 15 N 3 ) have been prepared: [Ru II L (dmso) 2 Cl]Cl (dmso = dimethyl sulfoxide), [Ru III LX 3 ] (X = C1 - , Br - ), [RuL 2 ](PF 6 ) 2 , [RuL(C 2 O 4 )I]. Hydrolyses of RuLCl 3 under a variety of reaction conditions afford dinuclear species: [Ru III 2 L 2 (μ-OH) 2 (μ-CH 3 CO 2 )]I 3 ·H 2 O , [Ru III 2 L 2 (μ-OH) 2 Cl 2 ](PF 6 ) 2 , and the mixed-valence species [Ru 2 L 2 (μ-Cl) 3 ](PF 6 ) 2 . The complex [Ru 2 L 2 (μ-OH) 2 (μ-CH 3 CO 2 )]I 3 -H 2 O has been characterized by a single-crystal X-ray diffraction study. The compound crystallizes in the monoclinic space group P2 1 /c with a = 14.70(1) Å , b = 19.00(1) Å , c = 9.714(7) Å , β = 99.62(7)°, and V = 2674 Å 3 , d calcd = 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 R 1 = 0.0615 and R 2 = 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 [Ru 2 L 2 (μ-OH) 2 (μ-CH 3 CO 2 )] 3+ and [Ru 2 L 2 (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 [Ru 2 L 2 (μ-OH) 2 (μ-CH 3 CO 2 )] 2+ has been characterized in solution.