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 [V^IVO(acac)₂] or [V^IVO(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 [V^IVO(L¹)(phen)] (1) and [V^IVO(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 [V^VO(L¹)(hq)] (3) and [V^VO(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 d_xy orbital. DFT studies for 3 indicate that the d_xy orbital of vanadium is the main contributor to the LUMO.

Keywords:

• V(IV) and V(V) complexes
• hydrazone complexes
• X-ray structure
• electrochemistry
• EPR spectra, DFT study

Acknowledgments

We thank University Grants Commission (New Delhi, India) for financial assistance. We are thankful to Dr P. Ghosh, Department of Chemistry, R.K. Mission Residential College, Narendrapur, India, for electrochemical measurements and to our College authority for providing research facilities. We are grateful to the learned reviewer 1 for his valuable suggestions. We gratefully acknowledge DST-FIST for instrumental help at R.K. Mission V.C. College, Rahara.

Disclosure statement

No potential conflict of interest was reported by the authors.