Ruthenium tris chelates with O,S-siderophores: synthesis, oxidation state, and electronic structure

Abstract

N-methylthiohydroxamic acids (RC(S)N(OH)Me), abbreviated HmeR (R = pH, p-C/sub 6/H/sub 4/OMe, CH/sub 2/Ph), react with RuCl/sub 3/ x 3H/sub 2/O in aqueous ethanol affording the green tris chelates Ru/sup III/(meR)/sub 3/. Cerium(IV) oxidation of these complexes in perchlorate media furnishes reddish pink Ru/sup IV/ (meR)/sub 3/ClO/sub 4/ x H/sub 2/O. The ruthenium(IV)-ruthenium(III) formal potential (E/sup 0//sub 298/) determined cyclic voltammetrically is approx. 0.4 V vs SCE. E/sub 298//sup 0/ of the ruthenium(III)-ruthenium(II) couple is approx. -1.0 V. Both redox couples are nearly reversible, suggesting the same gross stereochemistry for the three oxidation states. On the basis of comparative X-ray powder and IR data it is concluded that Ru(meR)/sub 3/ has facial stereochemistry. The Ru(meR)/sub 3/ complexes are low spin (S = 1/2; t/sub 2//sup 5/) and have rhombic EPR spectra. The EPR spectrum of Ru(ph)/sub 3//sup 3 -/ is rhombic but the three g values are closely spaced near 2 compatible with large net distortion. Two descriptions, viz. the ruthenium(IV)-stabilized ligand radical complex Ru/sup IV/(ph)/sub 2/(ph.)/sup -/ and the ruthenium(V) complex Ru/sup V/(ph)/sub 3//sup -/, are examined. The EPR spectrum is not incompatible with either description, but the Ru/sup v/(ph)/sub 3//sup -/ description has more favorable features. The thiohydroximate ligandmore » appears to be able to span all oxidation states of ruthenium from +2 to +5. 58 references, 4 figures, 5 tables.« less