Structural Characterization, DFT Calculations, Metal Uptake, Fluorescence, Antimicrobial and Molecular Docking Studies of Novel Co(II) and Ni(II) Complexes with NNS Tridentate Schiff base Ligand

Abstract A new Schiff base ligand N2-((5-methylthiophen-2-yl) methylene) pyridine-2,6-diamine (L) was prepared by condensation of 5-Methyl-2-thiophenecarboxaldehyde and 2,6-diaminopyridine in ethanol in a molar ratio 1:1. The ligand and its complexes were characterized based on elemental analyses, molar conductance, magnetic moment, IR, MS, 1H NMR, solid reflectance, and thermal analysis (TG and DTG) techniques. The complexes were found to have the formulas [CoL(H2O) Cl2].H2O and [NiL(H2O)Cl2].2H2O. From FTIR spectral data, the coordination between the ligand L to the central metal ion was through its nitrogen of pyridyl and azomethine and sulfur of 2-thiophenecarboxaldehyde. The metal complexes were found to be nonelectrolyte. Octahedral geometries of the Co(II) and Ni(II) complexes were investigated from electronic and magnetic data. The kinetic analysis of the thermogravimetric data was performed by using the Coats-Redfern equation. The fluorescence properties of the ligand and its complexes in DMF were studied. The values of optical band gap energy (Eg) of the synthesized complexes suggested that these compounds could be used as semiconductors. The adsorption of Co2+ and Ni2+ in aqueous solutions on ligand under various conditions was studied. The maximum adsorption percentage of Co(II) and Ni(II) were found to be 68% and 65%, respectively. The Molecular docking studies were executed to consider the nature of binding and binding affinity of the synthesized compounds with the receptor of Bacillus subtilis (gram +ve bacteria) and Escherichia coli (gram –ve bacteria) (PDB ID: 1fj4). The ligand and its complexes were tested as antimicrobial agents.