Synthesis, Spectroscopic Characterization, Thermal Behavior, and Antimicrobial and its Evaluation of Schiff Base Transition Metal Complexes Derived from Isonicotinic Acid Hydrazide

A novel Schiff base ligand, isonicotinic acid [1-(3,4-dimethoxyphenyl) ethylidene] hydrazide (INADPEH), was synthesized from condensation of isonicotinic acid hydrazide with 1-(3,4-dimethoxyphenyl)ethan-1-one. The Schiff base and its metal (Cobalt, Copper, Nickle, and Iron) complexes were characterized by elemental analysis, molar conductivity, magnetic moment values, UV-Vis, FTIR, and thermogravimetric analysis (TGA), and were obtained in good yields. The structure of the ligand was also confirmed by ¹ H NMR spectroscopy. Analytical and spectral data confirmed that INADPEH acts as a bidentate ligand, coordinating through the azomethine nitrogen and carbonyl oxygen. FTIR and UV-Vis spectra and magnetic susceptibility values collectively suggested predominantly octahedral geometries for the complexes. Thermal studies indicated stepwise decomposition of the complexes, with metal oxides as final residues. The antimicrobial activities of the compounds were tested against Escherichia coli, Staphylococcus aureus, Candida albicans , and Aspergillus niger. The antibacterial activity results revealed that the free ligand showed lower activity compared to the cobalt and copper complexes, with the copper complex exhibiting highest potency, surpassing the standard in some cases. This study highlights the enhanced biological efficacy arising from the significant role of metal complexation and recommends the potential applications of these hydrazone metal complexes as antimicrobial agents.