Synthesis, structure and solution chemistry of a family of dinuclear hydrazonato-vanadium(V) complexes with [OV(μ-O)VO]4+ core

Dinuclear trioxidic [{VOL}2μ-O] (1–4) complexes were synthesized from the reaction of [VIVO(acac)2] with an equimolar amount of H2L [H2L is the general abbreviation of hydrazone ligands (H2L1–4) derived from the condensation of benzoyl hydrazine with either 2-hydroxyacetophenone or its para substituted derivatives] in acetone or CH2Cl2 or acetonitrile. These V2O3L2 complexes were also obtained from the reaction of VOSO4 with H2L in the presence of two equivalents sodium acetate in aqueous-methanolic (50% V/V) medium and also from the decomposition of [VIVO(L)(bipy/phen)] complexes in CH2Cl2 solution. Black monoclinic crystals of 2 and 4 with C2/c space group were obtained from the reaction of [VIVO(acac)2], respectively, with H2L2 and H2L4 in acetone in which the respective ligands are bonded meridionally to vanadium in their fully deprotonated enol forms. The V–O bond lengths follow the order: V–O(oxo) < V–O(oxo-bridged) < V–O(phenolate) < V–O(enolate). Complexes (1–4) are diamagnetic exhibiting LMCT transition band near 380 nm in CH2Cl2 solution and they are electroactive displaying a quasi-reversible reduction peak in the 0.14–0.30 V versus SCE region. The λmax and the reduction peak potential (Epc) values show linear relationships with the Hammett constant (σ) of the substituents in the hydrazone ligands.These dinuclear complexes are converted to the corresponding mononuclear cis dioxo complexes K(H2O)+[VVO2(L)]− (5–8) and mixed-ligand [VVO(L)(hq)] complexes on reaction, respectively, with two equivalents KOH in methanol and two equivalents 8-hydroxyquinoline (Hhq) in CHCl3. Ascorbic acid reduces the dioxovanadium(V) complexes reversibly under aerobic condition.

Dinuclear [V2O3(L)2], 1–4 complexes with a family of hydrazone ligands (H2L1–4) have been synthesized by various synthetic routes. Electronic properties of these complexes exhibit linear relationships with the Hammett constant of the substituents in the ligands. These complexes can be converted to the corresponding complexes with VO2+ and VO3+ motifs.Figure optionsDownload as PowerPoint slide