title: An in Situ X-ray Absorption Fine Structure Study of Different Oxidation States of Oxo- and Hydroxo-Bridged Ruthenium Dimers in Acetonitrile Solution.
abstract: X-ray absorption fine structure (XAFS) experiments have been performed in acetonitrile solution with an in situ electrochemical cell at controlled electric potentials on [Ru(2)(&mgr;-O) (&mgr;-CH(3)COO)(2)(bpy)(2)L(2)](n)()(+) (bpy = 2,2'-bipyridine; L = pyridine (1) and 1-methylimidazole (2)) with the formal ruthenium oxidation states Ru(II)Ru(III), Ru(III)Ru(III), and Ru(III)Ru(IV). Spectra were also recorded for the corresponding hydroxo-bridged species, abbreviated as Ru(II)Ru(II)H, Ru(II)Ru(III)H, and Ru(III)Ru(III)H, which were formed by addition of p-toluenesulfonic acid to 1 and 2 and subsequent electrolysis. The X-ray absorption near edge structure (XANES) spectra all showed similar features, although a small shift toward higher threshold energy was observed with increasing formal ruthenium oxidation state. It is concluded from the analysis of the EXAFS data that the ruthenium-ruthenium distance of the &mgr;-oxo complexes decreases with decreasing formal ruthenium oxidation state, interpreted as resulting from decreased electrostatic repulsion between the ruthenium atoms. However, for the &mgr;-hydroxo complexes the ruthenium-ruthenium distance decreases in the order Ru(III)Ru(III)H > Ru(II)Ru(II)H > Ru(II)Ru(III)H. The present coordination structures of the oxo- and hydroxo-bridged ruthenium dimers of the different oxidation states are compared with related iron and vanadium dimers.
authors.affiliation: Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060, Japan.
authors.forename: Mats
authors.initials: M
authors.lastname: Valli
authors.forename: Seiya
authors.initials: S
authors.lastname: Miyata
authors.forename: Hisanobu
authors.initials: H
authors.lastname: Wakita
authors.forename: Toshio
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: Akihiro
authors.initials: A
authors.lastname: Kikuchi
authors.forename: Keisuke
authors.initials: K
authors.lastname: Umakoshi
authors.forename: Taira
authors.initials: T
authors.lastname: Imamura
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Sasaki