Synthesis of mixed-ligand complexes of VO2+ and VO3+ incorporating hydrazone, 1,10-phenanthroline and 8-hydroxyquinoline

Abstract

2-Aminobenzoylhydrazide (abh) reacts with equimolar amounts of either [VIVO(acac)2] or [VIVO(bzac)2] (where acac− and bzac− are the monoanionic forms of acetylacetone (Hacac) and benzoylacetone (Hbzac), respectively) in the presence of equimolar amounts of 1,10-phenanthroline (phen) to form the octahedral mixed-ligand complexes [VIVO(L1)(phen)] (1) and [VIVO(L2)(phen)] (2), where (L1)2− and (L2)2− are the dianionic forms of the 2-aminobenzoylhydrazone of acetylacetone (H2L1) and benzoylacetone (H2L2). Upon substituting phen by 8-hydroxyquinoline (Hhq), pentavalent [VVO(L1)(hq)] (3) and [VVO(L2)(hq)] (4) complexes were instead obtained. In the crystal structures of 3 and 4, the hydrazone ligands coordinate to the vanadium center through the enolic-O, one imine-N and amide-O in a mer geometry. The amine and the second imine nitrogen form intramolecular hydrogen bonds. Complexes 1 and 2 display quasi-reversible one-electron oxidation peaks near +0.60 V, while the pentavalent 3 and 4 exhibit quasi-reversible one-electron reduction peaks near −0.18 V versus Ag/AgCl in CH2Cl2 solution. EPR spectroscopic studies on 1 and 2 suggest that the unpaired electron is present in the dxy orbital. DFT studies for 3 indicate that the dxy orbital of vanadium is the main contributor to the LUMO.