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The reaction of vanadyl sulfate, VOSO4·H2O, with Schiff base ligand based on 2-hydroxybenzhydrazide and 5-bromosalicylaldehyde, with addition of 1,10-phenantroline as co-ligand, in ethanolic solution results in isolation of oxovanadium(IV) complex [VO(phen)L]·H2O (1). The complex was characterized by elemental analysis, single crystal X-ray structure measurements, IR, UV–Vis, EPR spectroscopy and cyclic voltammetry. Magnetic susceptibility measurements indicated the +4 vanadium oxidation state. The molecular structure of the complex was confirmed by single-crystal X-ray diffraction, revealing that the central vanadium atom was located in a six-coordinate distorted octahedral geometry. The stability of the complex at native pH and pH = 2.00 was also measured and the results are promising for application the vanadium complex as insulin mimetic compound.

Oxovanadium(IV) complexes have been synthesized by reacting vanadyl sulfate with Schiff bases derived from 4-amino-5-(substitutedphenoxyacetic acid)-1,2,4-triazole-3-thiol and benzil. All these complexes are soluble in DMF and DMSO; low molar conductance values indicate that they are non-electrolytes and characterized by elemental analysis, spectral techniques (UV–Vis, IR, EPR and XRD) and magnetic moment measurements. The EPR spectra indicate that the free electron is in dxy orbital. In vitro antifungal activity of ligands and synthesized compounds was determined against fungi Aspergillus niger, Colletotrichum falcatum and Colletotrichum pallescence and in vitro antibacterial activity was determined by screening the compounds against Gram-negative (Escherichia coli and Salmonella typhi) and Gram-positive (Staphylococcus aureus and Bacillus subtilis) bacterial strains. The antimicrobial activities have shown that the activity increases upon complexation.

The oxovanadium(II) complexes of the different vitamins like ascorbic acid (vitamin C; Vit. C), riboflavin (vitamin B2; Vit. B2) and nicotinamide (vitamin B3; Vit. B3) were synthesized and characterized by elemental analysis, molar conductance, IR, electronic, magnetic measurements, thermal studies, XRD and SEM. Conductance measurements indicated that the vanadyl(II) complexes of Vit. B2 and Vit. B3 are 1:2 electrolytes except for [VO(Vit. C) 2 (H 2 O) 2 ] complex is non-electrolyte. IR data show that Vit. B2 is bidentate ligand against azomethine nitrogen of pyrazine ring and C O of pyrimidine-2,4-dione but Vit. B3 and Vit. C acts as a monodentate ligand through pyridine nitrogen and hydroxo oxygen of furan ring, respectively. Electronic spectral measurements indicated that all VO(II) complexes have a square-pyramidal geometry. Magnetic measurements for the new vanadyl(II) complexes are in a good agreement with the proposed formula. Thermal analyses (TG/DSC) of the studied complexes show that the decomposition process takes place in more than two steps. XRD refer that VO(II) complexes have an amorphous behavior. The surface morphology of the complexes was studied by SEM. The antimicrobial activities of the ligands and its complexes indicate that the vanadyl(II) complexes possess high antibacterial and antifungal activities towards the bacterial species and the fungal species than start ligands.

Four new oxovanadium(IV) complexes, formed by the interaction of vanadyl sulfate pentahydrate and the Schiff bases derived from 3-methyl-1-phenyl-4-valeryl-2-pyrazolin-5-one and the sulfa drugs, N -(3′-methyl-1′-phenyl-4′-valerylidene-2′-pyrazolin-5′-one)sulfadiazine (L 1 H), N -(3′-methyl-1′-phenyl-4′-valerylidene-2′-pyrazolin-5′-)sulfaguanidine (L 2 H), N -(3′-methyl-1′-phenyl-4′-valerylidene-2′-pyrazolin-5′-one)sulphanilamide (L 3 H) and N ′(-3′-methyl-1′-phenyl-4′-valerylidene-2′-pyrazolin-5′-one)sulphamethoxazole (L 4 H) in aqueous ethanol are described. The resulting complexes were characterized by elemental analyses, molar conductances, magnetic and decomposition temperature measurements, cyclic voltammetry, electron spin resonance, infrared and electronic spectral studies. They have the composition [VO(L) 2 ]·H 2 O, where LH=Schiff base L 1 H, L 2 H, L 3 H or L 4 H mentioned above. A square–pyramidal structure having a slight ⋯V O⋯V O⋯ type interaction has been proposed for these complexes.