Synthesis, Spectroscopic Characterization, and Statistically Validated Antimicrobial Activity of a Novel Antimony(III) Complex with (Salycylaldehyde-p-toluidine-N-thiohydrazonato)[Sb(HSalptth)Cl3]

A novel antimony(III) complex, [Sb(HSalptth)Cl₃], incorporating the Schiff base ligand salicylaldehyde-p-toluidine-N-thiohydrazone (HSalptth), has been synthesized and comprehensively characterized. The ligand was prepared via condensation of salicylaldehyde with p-toluidine-N-thiohydrazide, followed by complexation with SbCl₃ under controlled conditions. The complex was isolated in good yield and characterized by elemental analysis, molar conductance, FT-IR, UV–Visible, and ¹H NMR spectroscopy, along with thermal analysis (TGA/DTA). Spectroscopic data reveal coordination of the monoanionic ligand to the Sb(III) center through the azomethine nitrogen and thiolate sulfur atoms, confirming bidentate chelation. The significant downward shift of the ν(C=N) band and changes in ν(C=S)/ν(C–S) frequencies in the IR spectrum support metal–ligand bond formation, while electronic transitions in the UV–Visible spectra are consistent with ligand to metal charge transfer processes. Molar conductance measurements indicate the non-electrolytic nature of the complex in polar solvents, suggesting a neutral coordination entity. Thermal studies demonstrate enhanced stability of the complex compared to the free ligand, with decomposition occurring in distinct stages corresponding to ligand fragmentation and chloride elimination. The in vitro biological activity of the ligand and its Sb(III) complex was evaluated against selected Gram-positive and Gram-negative bacterial strains as well as fungal species using the agar diffusion and minimum inhibitory concentration (MIC) methods. The antimony(III) complex exhibits significantly enhanced antimicrobial activity relative to the free ligand, which can be rationalized by chelation theory and increased lipophilicity facilitating membrane permeation. The results highlight the potential of antimony(III) thiohydrazone complexes as promising candidates for further pharmacological and antimicrobial investigations.