Synthesis and Antimicrobial Studies of Metal Complexes of Schiff Base Derived from 4-Acetylantipyrine and Three Substituted Anilines

Abstract

Three Schiff base ligands (HL1–HL3) were synthesized by condensation of 4-acetylantipyrine with three substituted anilines—4-chloroaniline, 4-nitroaniline, and 4-methoxyaniline—and their cobalt(II), nickel(II), and copper(II) complexes were prepared and characterized using melting point/decomposition temperature, percentage yield, molar conductance, elemental (C, H, N) analysis, magnetic susceptibility, infrared, and electronic spectroscopy. Molar conductance values (11.7–20.1 Ω⁻¹cm²mol⁻¹ in dimethyl sulfoxide) indicated the non-electrolytic nature of all complexes, consistent with coordinated chloride ions. Infrared spectral comparison showed a shift of the azomethine (C=N) stretching frequency to lower wavenumber upon complexation, confirming ligand coordination through the imine nitrogen, while new bands in the 420–540 cm⁻¹ region were assigned to M–N and M–O vibrations. Magnetic moment values (4.85–5.08 BM for cobalt(II), 3.05–3.26 BM for nickel(II), and 1.82–1.95 BM for copper(II)) supported octahedral geometry for the cobalt(II) and nickel(II) complexes and square planar geometry for the copper(II) complexes. Antimicrobial screening by the agar well diffusion method against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans showed that all metal complexes exhibited greater inhibitory activity than their corresponding free ligands, with copper(II) complexes consistently the most active, and the nitroaniline-derived ligand and its complexes showing the highest activity among the three ligand series, though all compounds remained less active than the standard reference drugs. These findings are consistent with chelation theory and support continued exploration of antipyrine-based Schiff base metal complexes as candidate antimicrobial agents.