Coordination mode variation of oximate in complexes of VO(OMe)2+ and VO2+ with biacetylmonoxime salicyloylhydrazone: Structural confirmation, properties and photocatalytic applications

Abstract

Reaction of equimolar amounts of bis(acetylacetonato)oxidovanadium(IV) [VO(acac)2] with biacetylmonoxime salicyloylhydrazone (H3L, where three dissociable protons represent the oxime, the amide and the phenol protons) in methanol produced the dimeric oxidomethoxidovanadium(V) complex [VO(μ-OMe)(HL)]2 (1) in 55% yield, while the same reaction in presence of two mole equivalents of KOH afforded a pervanadyl complex K[VO2(HL)]∙MeOH (2∙MeOH) in 60% yield. Both complexes were characterized by elemental analysis, mass spectrometry, magnetic susceptibility and electrical conductivity measurements, differential scanning calorimetry, various spectroscopy (IR, UV–Vis and 1H NMR) and cyclic voltammetry. The diamagnetic complexes are brown in color. In solution, 1 is non-electrolytic, while 2∙MeOH behaves as 1:1 electrolyte. In solid state, they remain thermally stable up to 132 and 269 °C, respectively. X-ray crystal structures of both 1 and 2∙MeOH were determined. In the centrosymmetric edge-shared bioctahedral 1, (HL)2− acts as fused 5,6-membered chelate rings forming amidate-O, imine-N and oximate-O donor. In contrast, (HL)2− acts as fused 5,5-membered chelate rings forming amidate-O, imine-N and oximate-N donor in trigonal-bipyramidal [VO2(HL)]−. The infrared and 1H NMR spectroscopic features of 1 and 2∙MeOH are consistent with their molecular structures. The electronic spectra of them in acetonitrile display several strong absorption bands within 452–207 nm. Cyclic voltammograms of the complexes and H3L in acetonitrile solutions show irreversible reduction responses with the Epc values in the potential range −0.9 to −1.5 V (vs. Ag/AgCl). Both complexes exhibit decent catalytic activity for photodegradation of rhodamine B (RhB) under visible light irradiation.