Paramagnetic ruthenium(III) complexes bearing O,O chelating ligands: Synthesis, spectra, molecular structure and electron transfer properties

Paramagnetic Ru(III) complexes of the type [RuX2(EPh3)(2)(L)] (where X = Cl or Br; E = P or As; L = monobasic bidentate benzophenone ligand) have been synthesized from the reaction of ruthenium(III) precursors. viz. [RuX3(EPh3)(3)] (where X = Cl, E = P; X = Cl or Br, E = As) or [RuBr3(PPh3)(2)(CH3OH)] and substituted hydroxy benzophenones in a 1:1 molar ratio in benzene under reflux for 6 h. The hydroxy benzophenone ligands behave as monoanionic bidentate O,O donors and coordinate to ruthenium through the phenolate oxygen and ketonic oxygen atoms, generating a six-membered chelate ring. The compositions of the complexes have been established by analytical and spectral (FT-IR, UV-Vis, EPR) and X-ray crystallography methods. The single crystal structure of the complex [RuCl2(PPh3)(2)(L-1)] (1) has been determined by X-ray crystallography and indicates the presence of a distorted octahedral geometry in these complexes. The magnetic moment values of the complexes are in the range 1.75-1.89 mu(B), which reveals the presence of one unpaired electron in the metal ion. EPR spectra of liquid samples at liquid nitrogen temperature (LNT) show a rhombic distortion (g(x) not equal g(y) not equal g(z)) around the ruthenium ion. The complexes are redox active and display quasi-reversible oxidation and quasi-reversible reduction waves versus Ag/AgCl. (C) 2011 Elsevier Ltd. All rights reserved.