Complexes of oxomethoxovanadium(V) with tridentate thiobenzhydrazide based Schiff bases

A family of complexes containing the {VO(OMe)}(2+) motif with the O, N, S-donor Schi. bases (H(2)tbhsR) derived from thiobenzhydrazide and 5-substituted salicylaldehydes has been reported. Reactions of [VO(acac) 2] with H2tbhsR in methanol provide the complexes having the general formula [VO(OMe)(tbhsR)] (R = H, OMe, Cl, Br and NO2) in 40-53% yields. Microanalytical, various spectroscopic (IR, UV-Vis and NMR) and electrochemical measurements have been used for the characterization of the complexes. All the complexes are redox active and display a near reversible metal centred reduction in the potential range 0.20-0.47 V (versus Ag/AgCl). The trend in these potential values reflects the polar effect of the substituent on the salicylidene fragment of tbhsR(2-). The X-ray crystal structures of all the complexes have been determined. In each of the complexes where R = H, OMe, Cl and Br, the metal ion is in a distorted square-pyramidal O3NS coordination sphere assembled by the O, N, S-donor tbhsR(2-), the methoxo and the oxo groups. The complex where R= NO2, crystallizes as a hexacoordinated species due to coordination of a methanol O-atom at the vacant sixth site. The bond parameters associated with the metal ions and the physical properties of the complexes are consistent with the +5 oxidation state of the metal ion in all the complexes. Scrutiny of crystal packing reveals dimeric, one-dimensional and two-dimensional self-assembled structures via intermolecular C-H center dot center dot center dot O and O-H center dot center dot center dot O interactions. The two-dimensional network contains the cyclic tetramer of methanol. (C) 2007 Elsevier B. V. All rights reserved.