Bioactive Ni(II), Cu(II) and Zn(II) complexes with an N3 functionalized Schiff base ligand: Synthesis, structural elucidation, thermodynamic and DFT calculation studies

Abstract

Some novel Ni(II), Cu(II) and Zn (II) metal complexes with new triaza Schiff base ligand (N-(2quinolylmethylidene)-4X-2-aminobenzene)imine (where X = Me, Cl, NO2)) have been synthesized. Various spectral techniques such as elemental analysis, magnetic susceptibility, conductivity, 1HNMR, IR, UV–Vis spectra, Mass spectrometry, powder XRD and EDX were used to confirm the structures. It has been found that the Schiff base behaves as a tridentate ligand forming chelates with 1:1 metal:ligand stoichiometry. The prepared Schiff base compounds were screened in vitro for their antibacterial activity against a number of pathogenic Gram positive and Gram negative bacteria, namely S.aureas and E.coli. The complexes show more potent activities than their free ligands. Spectrophotometric method and SQUAD program were applied to extract thermodynamic parameters to explain the complex formation behavior in solution at 25 °C in constant ionic strength (I = 0.1 M NaClO4). Also, density functional theory calculations at different level of DFT and basis set were employed to investigate optimized geometry, vibrational frequency analysis, electronic structure (energy of the HOMO and LUMO, Mulliken atomic charge, dipole moment, hardness and softness, electrophilicity and spectral properties) of the prepared Schiff base compounds. The DFT results showed that proposed structure and stability in ligands and their complexes are in accord with the experimental outcomes.