Synthesis, characterization, electrochemical studies and antimicrobial activities of metal complexes

Metal complexes of Schiff base 4-[(2, 4-dihydroxy-benzylidene)-amino]-1, 5-dimethyl-2-phenyl-1, 2-dihydroxo-pyrazol-3-one (H2L) derived from condensation of 2,4-dihydroxybenzaldehyde and 4-aminoantipyrine were synthesized and characterized by FT-IR spectra, elemental analysis, 1H &13C NMR, mass spectra, UV–Visible, X-ray diffraction, molar conductance, magnetic moment and thermal analysis (TGA). The elemental analysis proved that the complexes have the general formulae of [M(HL)(X)(OH2)]2, where M = Cu(II); X = OAc−(1); NO3−(2); Cl−(3), M = Co(II) (4), Mn(II) (5); X = OAc and {[UO2(HL)]2.2(OAc)}(6). According to the FT-IR spectra data, it was found that the H2L ligand is coordinated to the metal ions in a tridentate donor sites of the nitrogen atom of azomethine group, the oxygen atom of phenolic group and the oxygen atom of carbonyl group. From the measurements of magnetic susceptibility and electronic spectral data, it is found that these complexes are octahedral geometries. The trend in g value (g║ ˃ g⊥ ˃ 2.00) suggests that the unpaired electron on copper has dx2-y2 character and the complexes have an octahedral structure. By comparing the synthesized ligand (H2L) to its metal complexes was screened for their antibacterial activity against Klebsiella pneumoniae, Escherichia coli, Pseudomonas sp., Bacillus cereus and Staphylococcus aureus. It was found that the metal complexes had more potent antimicrobial than the parent Schiff base ligand against one or more microbial species. Some complexes showed higher activity than ligand. The complex (3) has antibacterial activities against Bacillus cereus, Klebsiella pneumoniae and Staphylococcus aureus. The antibacterial activity of complex (3) was the highest ones than the ligand and other complexes as well as penicillin G against Klebsiella pneumoniae. Antifungal activities were determined against Fusarium oxysporum, Aspergillus niger and Candida albicans. The inhibition efficiency of the prepared ligand (H2L) against the corrosion of carbon steel in HCl (2 M) solution was determined by various electrochemical techniques.