Crystal structure, computational insights, and biological activities of thiazole-based hydrazone zinc(II) complexes

In the search for novel bioactive molecules, we synthesized a new zinc(II) complex, [ZnL(NCS)(H2O)], and reinvestigated a previously reported complex, [ZnL2], both derived from a hydrazone ligand obtained via the condensation of 2-acetylthiazole and thiosemicarbazide. Comprehensive structural characterization was performed using single-crystal X-ray diffraction and spectroscopic techniques (FTIR, UV–Vis, NMR). In both mononuclear complexes, the ligand coordinates in its deprotonated form (L–) via an NNS donor set. The newly synthesized complex adopts a distorted square-based pyramidal geometry, whereas the previously reported complex exhibits octahedral coordination. To further understand their structural properties in DMSO solution, where all spectroscopic and biological studies were conducted, density functional theory (DFT) calculations were performed. The cytotoxic potential of the complexes was evaluated against five human cancer cell lines (HeLa, A549, MDA-MB-231, K562, LS 174 T) and normal fibroblasts (MRC-5). Additionally, their antibacterial and antifungal activities were assessed against a range of Gram-positive and Gram-negative bacteria, fungal strains, and yeast. The findings highlight the impact of structural differences on the biological properties of these Zn(II) complexes, offering valuable insights into their potential applications.