Ternary pentagonal-bipyramidal oxovanadium(V) complexes containing five- and six-membered chelate rings: Syntheses, structures and properties

Abstract

Reactions of bis(acetylacetonato)oxovanadium(IV) [VO(acac)2] with isolated or in-situ generated α-diketone bis(para-R-benzoylhydrazones) (H2Ln (n = 1–6), where 2H represent the two dissociable amide protons) in methanol or chloroform–methanol (1:3) mixture afford six novel oxovanadium(V) complexes of formula [VO(acac)(Ln)] (1–6) in 51–64% yields. All the complexes have been characterized by elemental analysis, mass spectrometric, solution electrical conductivity, various spectroscopic (IR, UV–Vis, and 1H NMR) and cyclic voltammetric measurements. The complexes are brown in color. They are diamagnetic and non-electrolytes. Molecular structures of all six complexes have been determined by single crystal X-ray crystallography. The metal center in each complex is in a distorted pentagonal-bipyramidal N2O5 coordination sphere. The fused 5,5,5-membered chelate rings forming ON2O-donor (Ln)2− and one of the acetylacetonate-O form a N2O3 pentagonal plane around the vanadium atom, while the second acetylacetonate-O and the oxo atom occupy the two axial positions. In the crystal lattice, the complexes form one-dimensional chain-, ladder- and ribbon-like supramolecular structures via various types of intermolecular non-covalent interactions such as trifurcated OH∙∙∙(O,O,O), bifurcated CH∙∙∙O∙∙∙HC and CH∙∙∙(O,O), simple CH∙∙∙O, π−π, CH∙∙∙π and O∙∙∙O interactions. The spectroscopic features of 1–6 are consistent with their molecular structures. All the complexes are redox active and display a quasi-reversible to irreversible vanadium(V) to vanadium(IV) reduction in the potential range −0.80 to −0.92 V (vs. Ag/AgCl).