Synthesis, characterization, biological activity, DFT studies on transition metal complexes derived from 5,5′-(propane-1,3-diylbis(sulfanediyl))bis(1,3,4-thiadiazol-2-amine) ligand and its corrosion inhibition study on carbon steel

Abstract

The goal of our research was to create new ligand-metal complexes that could be characterized using various physicochemical techniques like elemental analyses, molar conductivity, magnetic susceptibility, infrared (IR), electronic absorption, 1H NMR, mass spectral studies and thermal analysis. The analytical data and mass spectra of the ligand and the complexes confirm the stoichiometry of metal complexes as being of the metal to ligand ratio is 1:1. The magnetic measurements and spectral studies evidenced the octahedral geometry of the complexes. The ligand was found to be neutral tetradentate and coordinated to the metal ions in NNSS mode via the two-amine nitrogen and two sulfur atoms as revealed from the IR spectral studies. The decomposition of the ligand and the complexes were discussed according to the data obtained from thermogravimetric analysis within the temperature range from room temperature to 1000 °C. The antimicrobial, antioxidant and anticancer assay have been explored and the minimum inhibitory concentration (both liquid and Disc method) of organic ligand and its metal complexes against various microbial pathogens were reported. Most of the metal complexes showed comparable activities and, in some cases, greater activity against tested organisms. Ni(II) (26.7±0.6 mm/mg), Ni(II) (30.0±1.0 mm/mg), Cd(II) (30.3±0.6 mm/mg) and Ni(II) (21.3±0.6 mm/mg) complexes had the highest activity against Escherichia coli, Klebsiella pneumonia, Staphylococcus aureus and Streptococcus mutans organisms even better than the standards. The Cu(II) (IC50 = 6.49 µg/mL) and Cd(II) (IC50 = 7.62 µg/mL) complexes showed the highest anticancer effect than the other complexes. The results showed the superior activity of the complexes over the ligand in accordance with the chelation theory. The inhibition activity of ligand was studied in acid medium used by impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), and electrochemical potentiodynamic polarization (PDP), and the results obtained evidenced the success of the ligand for inhibiting the corrosion of steel.