Co(II), Ni(II), and Cu(II) Complexes Containing Isatin-Based Schiff Base Ligand: Synthesis, Physicochemical Characterization, DFT Calculations, Antibacterial Activity, and Molecular Docking Analysis

Abstract— Schiff base ligand [3-(2-hydroxyphenylimino)-1,3-dihydroindol-2-one] was synthesized by the condensation reaction of isatin with 2-aminophenol. The Schiff base and its metal complexes with Co(II), Ni(II), and Cu(II) and ions were permeated by ¹H NMR, IR, elemental analysis, ESI-MS spectroscopy, electronic spectroscopy, and some physicochemical measurements. The Schiff base behaved as a tridentate ligand in all metal complexes and was linked by azomethine nitrogen (=C=N). Supported by analytical data the metal-ligand stoichiometry in the formation of complexes was found as 1 : 2 molecular ratio. Based on analytical data allied with spectroscopic studies spilled that the Cu(II) complex preferred tetrahedral geometry, while Ni(II) and Co(II) complexes offered square planar and octahedral geometry, respectively. The complexes were undergone thermal analysis (TGA and DTG); complexes were found thermally stable up to 200°C. All the stable assembled compounds were assessed for antibacterial competency. The ligand and the complexes were played mild to sturdy antibacterial activity against numerous pathogenic bacterial species, although growth inhibitory activities of complexes were enhanced comparatively than their respective ligands. Additionally, molecular docking analysis and quantum computational calculations based on the density functional theory (DFT) approach were used to study the molecular characteristics of the novel complexes and provide in-depth insights into their involvement in their ability to restrict bacterial growth.