Synthesis, Characterization, and Antibacterial Evaluation of Dinuclear Organotin(IV) Complexes Derived from Oxalyldihydrazone-Based Ligands

In this study, three novel oxalyldihydrazone-based ligands were synthesized through the condensation of oxalyldihydrazide with three different aldehydes: 5-bromo-2-hydroxybenzaldehyde, 2-hydroxynaphthaldehyde, and 2-hydroxy-3-methoxybenzaldehyde. These ligands were subsequently reacted with two equivalents of dimethyltin(IV) dichloride, resulting in the formation of symmetrical dinuclear organotin(IV) complexes in a 1:2 metal-to-ligand molar ratio. The synthesized ligands and their corresponding complexes were fully characterized using FT-IR spectroscopy, ¹H NMR, ¹¹⁹Sn NMR, and elemental analysis. The spectral data confirmed successful coordination of the tin centers with donor atoms of the ligands, consistent with the proposed dinuclear structures. The antibacterial activities of the ligands and complexes were evaluated against both Gram-positive bacteria (*Staphylococcus aureus*, *Bacillus subtilis*) and Gram-negative bacteria (*Escherichia coli*, *Pseudomonas aeruginosa*). Notably, the organotin(IV) complexes displayed significantly enhanced antibacterial activity compared to their free ligands, especially against *P. aeruginosa*, a clinically important multidrug-resistant pathogen. This enhanced activity is attributed to the chelation effect, which increases the lipophilicity of the complexes, thus improving their ability to penetrate bacterial cell membranes. Furthermore, the proposed mechanism involves hydrolysis of the organotin complexes in biological media, allowing interaction with cellular enzymes and disruption of bacterial metabolic pathways. The findings suggest that these novel organotin(IV) complexes are promising candidates for further development as potent antibacterial agents.