Synthesis, structure and solution chemistry of dioxidovanadium(V) complexes with a family of hydrazone ligands. Evidence of formation of centrosymmetric dimers via H-bonds in the solid state

[VIVO(acac)2] reacts with the methanol solution of tridentate ONO donor hydrazone ligands (H2L1–4, general abbreviation H2L; are derived from the condensation of benzoyl hydrazine with 2-hydroxyacetophenone and its 5-substituted derivatives) in presence of neutral monodentate alkyl amine bases having stronger basicity than pyridine e.g., ethylamine, diethylamine, triethylamine and piperidine (general abbreviation B) to produce BH+[VO2L]− (1–16) complexes. Five of these sixteen complexes are structurally characterized revealing that the vanadium is present in the anionic part of the molecule, [VO2L]− in a distorted square pyramidal environment. The complexes 5, 6, 15 and 16 containing two H-atoms associated with the amine-N atom in their cationic part (e.g., diethylammonium and piperidinium ion) are involved in H-bonding with a neighboring molecule resulting in the formation of centrosymmetric dimers while the complex 12 (containing only one hydrogen atom in the cationic part) exhibits normal H-bonding. The nature of the H-bonds in each of the four centrosymmetric dimeric complexes is different. These complexes have potential catalytic activity in the aerial oxidation of l-ascorbic acid and are converted into the [VO(L)(hq)] complexes containing VO3+ motif on reaction with equimolar amount of 8-hydroxyquinoline (Hhq) in methanol.

Among the sixteen dioxidovanadium(V) complexes of the type (alkyl amineH+) [VO2(benzoyl hydrazone)]− reported here, the H-bonded centrosymmetric dimeric dioxidovanadium(V) complexes have been found to exist in the solid state only with diethylamine and piperidine. All these complexes exhibit ascorbic acid oxidase activity.Figure optionsDownload as PowerPoint slide