Nano-sized, ternary oxovanadium(IV) complexes containing electron-rich oxygen-based ligands

Abstract

Some mononuclear mixed-carboxylato β-diketonato oxovanadium(IV) complexes of the general formula [VO(β-dike)(RCOO)] (where Hβ-dike = acetylacetone; benzoylacetone or dibenzoylmethane, R = C15H31 or C17H35) have been synthesized from VO(acac)2 by stepwise substitutions of acetylacetonate ion with straight chain fatty acids (RCOOH) and β-diketones in p-xylene under reflux. The substituted acetylacetone could be fractionated out with p-xylene as an azeotrope. These were characterized by elemental analyses, molecular weight determinations, spectral (electronic, infrared, 1H NMR, EPR and powder XRD) studies, magnetic susceptibility measurements and cyclic voltammetry. Molar conductance values indicated the complexes to be non-electrolytes in nitrobenzene. Bidentate chelating nature of β-diketonate and carboxylate ligands in the complexes was established by infrared and NMR spectra. Molecular weight determinations confirmed mononuclear nature of the complexes. The EPR spectra illustrated coupling of the unpaired electron with 51V nucleus (I = 7/2). Cyclic voltammograms of all the complexes displayed one-step oxidation processes. The oxidation peak potential corresponded to the quasireversible one-electron oxidation process of the metal center, yielding V(V) species. Powder XRD and transmission electron microscopy (TEM) studies indicated the particles of these were lying in the nano-size range. The synthesized complexes are a new type of mixed-ligand complexes in which vanadium is having coordination number 5. A square pyramidal geometry around vanadium has been assigned in all the complexes.