Synthesis, Characterization and Biological Studies of Copper, Nickel, Cobalt and Zinc Complexes of a Schiff Base Ligand Derived from 4‑Chloro‑2‑mercaptobenzaldehyde and 4‑Aminoantipyrine

Abstract

A new Schiff base ligand (H L) was synthesized by condensation of 4‑chloro‑2‑mercaptobenzaldehyde with 4‑aminoantipyrine and subsequently coordinated with Cu(II), Ni(II), Co(II) and Zn(II) salts to produce a series of metal complexes with the general formula [M(L)] 2X^- (M = Cu, Ni, Co, Zn; X = OAc⁻). The ligand and complexes were characterized by elemental analysis, molar conductivity, magnetic susceptibility, FTIR, UV–Visible, ¹H NMR (where applicable), mass spectrometry, ESR (for Cu(II)), and thermogravimetric analysis (TGA). Spectral data indicate that the Schiff base behaves as a bidentate ligand coordinating through the azomethine nitrogen and carbonyl oxygen atoms formed geometries as square‑planar/tetragonally distorted for Cu(II) Ni(II) and Co(II), while Zn(II) complexes are suggested to be tetrahedral. Biological activities were evaluated by antimicrobial screening against Gram‑positive and Gram‑negative bacteria and selected fungi, antioxidant activity using the DPPH radical scavenging assay, and Superoxide Dismutase (SOD)‑like activity. The metal complexes showed enhanced antimicrobial and antioxidant activities compared to the free ligand, with the Cu(II) complex demonstrating the most pronounced biological effects. Thermal behavior showed stepwise degradation with formation of metal oxide residue. The structural and biological profiles suggest potential applications of these complexes as biologically active coordination compounds.