Synthesis, Characterization, Thermal Behavior, and Antimicrobial Activity of Transition Metal Complexes Derived from a Sulfonamide–Based Schiff Base Ligand

Transition metal complexes of Co(II), Cu(II), Ni(II), and VO(IV) were synthesized using a novel Schiff base ligand derived from the condensation of 4,4’-sulfonyldianiline and (2,4-dihydroxyphenyl)(phenyl)methanone. The ligand and its metal complexes were thoroughly characterized using elemental analysis, FTIR, UV-Vis, 1H-NMR, and mass spectroscopy, confirming their structural integrity. Spectroscopic studies revealed that the ligand coordinates to the metal ions in a bidentate manner through the azomethine nitrogen (–C=N–) and phenolic oxygen (–O–) atoms, forming stable chelates. Thermogravimetric analysis (TGA) was performed under a nitrogen atmosphere at a heating rate of 10°C min⁻¹, demonstrating the thermal stability and decomposition patterns of the complexes. Kinetic parameters for thermal degradation were calculated using the Freeman-Carroll and Sharp-Wentworth methods, providing insights into their thermal behavior. The antimicrobial activity of the ligand and its metal complexes was evaluated against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae) bacteria using the agar well diffusion method. The Cu(II) complex exhibited the highest inhibitory effect, particularly against S. aureus, suggesting enhanced bioactivity upon metal coordination. This study highlights the structural, thermal, and biological properties of sulfonamide-based Schiff base metal complexes, emphasizing their potential as antimicrobial agents and contributing to the broader understanding of coordination chemistry in medicinal applications.