97751-78-5Relevant academic research and scientific papers
Ruthenium tris chelates with O,S-siderophores: Synthesis, oxidation state, and electronic structure
Bhattacharya, Samaresh,Ghosh, Phalguni,Chakravorty, Animesh
, p. 3224 - 3230 (2008/10/08)
N-Methylthiohydroxamic acids (RC(S)N(OH)Me), abbreviated HmeR (R = Ph, p-C6H4OMe, CH2Ph), react with RuCl3·3H2O in aqueous ethanol affording the green tris chelates RuIII(meR)3. Cerium(IV) oxidation of these complexes in perchlorate media furnishes reddish pink RuIV(meR)3ClO4·H2O. The ruthenium(IV)-ruthenium(III) formal potential (E°298) determined cyclic voltammetrically is ～0.4 V vs. SCE. The wine red ruthenium(II) species Ru(meR)3- are also accessible voltammetrically but are too unstable to be isolated. E°298 of the ruthenium(III)-ruthenium(II) couple is ～-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)3 has facial stereochemistry. The Ru(meR)3 complexes are low spin (S = l/2; t25) and have rhombic EPR spectra. The axial distortion parameter Δ is found to be large and positive (～6000 cm-1). The ground state is nearly pure A in character. The rhombic splitting is ～1500 cm-1. In near-IR spectra Ru(meR)3 has a weak (∈ ～ 100) band at ～ 1500 nm with signs of a second band at lower energies. These are assigned to transitions within the Kramers doublets. The ruthenium(IV) cation Ru(meR)3+ is paramagnetic (S = 1; t24) but is EPR silent, probably due to fast relaxation. The thiohydroxamic acid PhC(S)N(OH)H, abbreviated H2ph, affords low-spin red-violet Na[Ph4As]2[RuIII(ph)3]·H 2O and blue Na[Ph4As] [RuIV(ph)3]·H2O. Here the ruthenium(IV)-ruthenium(III) formal potential is unusually low, -0.16 V, and the ruthenium(III)-ruthenium(II) E°298 is -1.17 V. The EPR spectrum of Ru(ph)33- is rhombic but the three g values are closely spaced near 2 compatible with large net distortion. Two low-intensity optical bands at 1430 and 1180 nm corresponding to transitions within the Kramers doublets can be recovered by Gaussian analysis. The RuIV(ph)32- ion undergoes a nearly reversible one-electron oxidation (E°298 = 0.62 V) to deep blue, unstable, and EPR-active Ru(ph)3- (a slightly asymmetric signal at g ～ 2). Two descriptions, viz. the ruthenium(IV)-stabilized ligand radical complex RuIV(ph)2(ph·)- and the ruthenium(V) complex RuV(ph)3-, are examined. The EPR spectrum is not incompatible with either description, but the RuV(ph)3- description has more favorable features. The thiohydroximate ligand appears to be able to span all oxidation states of ruthenium from +2 to +5.
