Synthesis, characterization, reactivity, and catalytic studies of heterobimetallic vanadium(V) complexes containing hydrazone ligands

Abstract

Six heterobimetallic alkali metal dioxidovanadium(V) coordination polymer complexes {[M6{VO(μ-O)}2(μ-OH)4(μ4-slox/nph)].n DMF}∞ where M = Na, K, and Cs; n = 1 for (1), 0 for (2)-(6) of two dihydrazone ligands, disalicylaldehydeoxaloyldihydrazone (H4slox) and bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone (H4nph) are reported. All the complexes have been characterized by various physicochemical techniques such as elemental analyses, molar conductance, IR, NMR, UV–vis, and cyclic voltammetry. The IR, 1HNMR, and 13CNMR spectral data suggest that the dihydrazones are coordinated through phenolate/naphtholate oxygen, enolate oxygen, and azine nitrogen atoms to the metal centres. The structure of complex {[Na6{VO(μ-O)}2(μ-OH)4(μ4-slox)].DMF}∞ (1) is also determined by single-crystal X-ray data, which revealed that the H4slox coordinated via all possible dative sites to metal centres as tetrabasic octadentate ligand. The vanadium metal centres adopted distorted square-pyramidal coordination geometries, and the sodium atoms are also in five coordination atmospheres. The electronic spectra of the complexes showed LMCT bands in addition to intra-ligand π → π* and n → π* transitions. As evident from the cyclic voltammetry, the complexes showed two metal-centred electron transfer reactions {[(VVVV(slox)2−/VVVIV(slox)3−] and [(VVVIV(slox)3−/VVVIV(slox)4−]}, in addition to the ligand centred electron transfer reactions. Further, bovine serum albumin (BSA interaction studies of the complexes {[Na6{VO(μ-O)}2(μ-OH)4(μ4-slox)].DMF}∞ (1) and [Na6{VO(μ-O)}2(μ-OH)4(μ4-nph)]∞ (4) revealed strong binding affinity. Moreover, the catalytic studies of the complexes (1) and (4) were found to be effective for the oxidation of alcohols into their corresponding aldehydes and ketones and bromination of some organic substrates in the presence of H2O2 as an oxidizing agent.