From coordination-induced tautomerism to therapeutics: Structural, supramolecular, and antimicrobial insights into a Hg (II)-thiosemicarbazone complex

A new Hg(II) complex 1 was synthesised from a 3-methoxysalicylaldehyde-4-methylthiosemicarbazone ligand (H2L) via one-pot reaction and characterized by FT-IR, 1H NMR, mass spectroscopy, elemental analysis, and single-crystal X-ray diffraction analysis. The complex 1 adopts a distorted seesaw [HgN2S2] coordination geometry. Coordination to Hg(II) promotes a thione-thiol tautomeric conversion in the ligand (H2L), forming a deprotonated thiolate donor. Structural analysis, combined with Hirshfeld surface and enrichment ratio evaluations, unveiled that O & ctdot;H and C & ctdot;C contacts play dominant roles in supramolecular stabilization. Density Functional Theory (DFT) analysis suggests a substantial amount of charge transfer from H2L to Hg(II). These results highlight how the interplay between coordination-induced tautomerism and noncovalent forces governs the molecular organization of the Hg(II) complex. Furthermore, the antibacterial efficacies of Hg(II) complex 1 and the free ligand (H2L) towards Gram-positive bacterial strains (viz. Staphylococcus cohnii, Mammaliicoccus lentus, Bacillus cereus, and Corynebacterium stationis) and Gram-negative bacterial strains (viz. Klebsiella pneumoniae, Enterobacter cloacae, Salmonella enterica, and Shigella sonnei) have been evaluated. Moreover, to explore the mechanism of the antibacterial action of 1, time-kill kinetic assay, deoxyribonucleic acid (DNA) cleavage potential, and molecular docking studies are performed.