Simultaneous formation of non-oxidovanadium(iv) and oxidovanadium(v) complexes incorporating phenol-based hydrazone ligands in aerobic conditions

A new family of non-oxidovanadium(iv) [V-IV(L)(2)] (1-4) complexes along with methoxy bonded oxidovanadium(v) [(VO)-O-V(L)(OCH3)] (5 and 6) and [(VO)-O-V(L)(OCH3)](2) (7 and 8) complexes have been synthesized by refluxing [(VO)-O-IV(aa)(2)] [aa(-) being the deprotonated form of acetylacetone (Haa)] with a family of hydrazone ligands (H2L1-4, general abbreviation H2L, obtained by the condensation of 2-aminobenzoylhydrazide with 2-hydroxyacetophenone and its 5-substituted derivatives) using laboratory grade methanol as a solvent in the presence of air in similar to 30% yield. The DFT calculated changes in Gibbs free energy (Delta G), enthalpy (Delta H) and internal energy (Delta E) for the reaction to form complexes 1-4 in methanol: 2H(2)L + [(VO)-O-IV(aa)(2)] + 1/4O(2) + CH3OH -> [V-IV(L)(2)] + 2Haa + CH3OH + 1/4O(2) are on average similar to 10, similar to 5 and similar to 14 kcal mol(-1) respectively, while these values for the reaction in methanol to form complexes 5-8: 2H(2)L + [(VO)-O-IV(aa)(2)] + 1/4O(2) + CH3OH -> [(VO)-O-V(L)(OCH3)] + H2L + 2Haa + 1/2H(2)O are on average similar to-16, similar to-20 and similar to-12 kcal mol(-1) respectively, suggesting that the formation of 1-4 is not thermodynamically feasible through this method. In practice, however, these complexes are also formed probably due to their very low solubility in methanol along with complexes 5-8. The complexes were characterized by analytical and spectral methods. The structures of the H2L2 and H2L3 ligands and complexes 3 and 5-8 were determined by X-ray diffraction. Complexes 1-4 display quasi-reversible one-electron oxidation and reduction peaks in the potential windows of 0.66-0.70 and -0.22 to -0.39 V respectively while complexes 5-8 exhibit quasi-reversible one-electron reduction peaks in the 0.15-0.22 V region. The EPR spectral parameters indicate that the odd electron in complexes 1-4 is present in the d(xy) orbital, a suggestion which is also supported by a DFT study. The substituents in the aryloxy ring of the hydrazone ligands exhibited a significant effect on lambda(max) for the LMCT transition, A(||), E-1/2, E-SOMO/E-HOMO and E-LUMO of the complexes. Complexes 1, 3, and 5-7 showed a wide range of toxicity in a dose dependent manner against lung cancer cells and they kill the cells through apoptosis. The binding ability of the complexes with CT DNA has been determined by a fluorescence emission study and the binding constant value obtained by this method was supported by a molecular docking study.