Synthesis, Characterization, Powder X-Ray Diffraction Analysis, ESR Study, Thermal Stability of Ni(II) and Fe(III) Schiff Base Ligand Complexes and Potency Study as Antibacterial and Antioxidant Agents

The salen-type Ni(II) and Fe(III) complexes were successfully syntheses by using Schiff base ligand [E]-2,2'-((pentane-1,3-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(naphthalen-1-ol) (L1) and its derivatives (L2) and (L3). Due to their chelating properties and ability to coordinate with a wide range of transition metal ions of different oxidation states, they are considered an important family of organic compounds. The structure of the metal complexes was elucidated by different spectral techniques (FT-IR, H-1 NMR, mass spectrometry, UV-visible, powder X-ray diffraction, DGA-TGA, and ESR). The powder X-ray diffraction data revealed that Ni(II) complexes are arranged in a triclinic system while Fe(III) complexes are in a monoclinic system with space group P1. TGA-DTA study suggests that the Ni(II) ion does coordinate with the N2O2 Schiff base ligands with coordination number 4. Also, the Fe(III) ion does coordinate with the N2O2 Schiff base ligands with coordination number 6. The Ni(II) complex exhibits the square planar geometry with unpaired electron lying in the dx(2)-y(2) orbital. The EPR spectra of Fe(III) complexes may suggest an octahedral structure around the Fe(III) ion. The antibacterial activity was tested against different pathogens and confirmed that the presence of the -I and -NO2 group with N2O2 donor Schiff bases ligand are responsible for strongly inhibiting bacterial growth of metal complexes. The Ni(II) complexes showed higher potency antioxidant activity, indicating that the Ni (II) complexes exhibited more prominent antioxidant activity than the Fe (III) complexes.