STUDIES ON VANADIUM (V), MOLYBDENUM (VI) AND TUNGSTEN (VI) DIOXO AND PEROXO COMPLEXES OF POLYDENTATE LIGANDS

Abstract

Stirring of V205 in an aqueous solution of KOH and 30% H202 results in the formation of oxoperoxovanadium(V) species, [V0(02)2.X H20]. Reaction of this species with 2-(a-hydroxymethyl)benzimidazole or 2-(a-hydroxyethyl)benzimidazole in 1:2 molar ratio gives the complex K[VO(02)L2] (where LH = ligand). Similar peroxo species of molybdenum and tungsten generated in situ by stirring, MoO3 or W03.H20 with an excess of 30% H202 readily react with 2-(a-hydroxyethyl)benzimidazole in aqueous alcoholic solution to give the corresponding peroxo complexes of formula [MO(02)L2] (where M = Mo or W). All these complexes are crystalline in nature and light yellow to orange in colour. These complexes exhibit three IR active vibrational modes — 860 cm-1, 760 cm-1 and 600 cm-1 which are characteristic of 112-coordinated peroxo group. Reaction of [M02(acac)2] (where M = Mo or W, acacH = acetyl acetone) with the above ligands along with 2-(a-hydroxybenzyl)benzimidazole gives the corresponding dioxo complexes of general formula [MO2L2]. These complexes are dominated by the presence of two sharp bands — 900 cm-1 region due to vsym (0—M=0) and easy,,, (0--M=0) modes. The IR spectra also confirms the monobasic ON bidentate behaviour of the ligands. A broad band' at — 420 nm in peroxovanadium(V) complexes, while at — 350 nm in peroxomolybdenum(VI) and tungsten(VI) complexes has been assigned due to the peroxo-metal charge transfer (LMCT) band.