Study of mixed-ligand hydrazonato-oxovanadium(V) complexes incorporating salicylaldehyde as co-ligand

In the present paper [VO(acac)2] reacts with an equimolar amount of tridentate dibasic ONO donor hydrazone ligand derived from the condensation of benzoyl hydrazine with either 2hydroxyacetophenone (H2L 1) or its para-substituted derivatives (H2L 2) (general abbreviation H2L), in the presence of excess amount of salicylaldehyde (Hsal) in methanol under aerobic conditions producing the mixed-ligand [VVO(L)(sal)], complexes (1)-(4) in good yields. The complexes are diamagnetic indicating the pentavalent state of vanadium and exhibit only LMCT transition band near 440 nm in addition to intra-ligand (π→π*) transition band near 330 nm in CH2Cl2 solution. IR spectra of these complexes in KBr disc and their 1H NMR spectra in CDCl3 solution indicate the presence of two isomeric forms for each of these complexes in different proportions. λmax(for the LMCT transition) and redox potentials of these complexes are linearly related to the Hammett constants (σ) of the substituents in the aryloxy ring of the hydrazone ligands.