Synthesis, cytotoxicities, structural properties and comparison of dihalogeno-substituted-thiosemicarbazone ligands and mixed-ligand Ni(<scp>ii</scp>) complexes

Three novel mixed-ligand Ni(ıı) complexes were synthesized from a 3,5-dihalogenosalicylaldehyde-<i>S</i>-methyl isothiosemicarbazone ligand (3,5-dichloro for Complex I, 3,5-dibromo for Complex II, and 3,5-diiodo for Complex III) and diethanolamine. The synthesized compounds were characterized by elemental analysis, FT-IR, UV-Vis and ¹H-NMR spectroscopy. Solid-state structures of Complex I and Complex II were determined by the single-crystal X-ray diffraction technique. Both the complexes were found to have a distorted square planar geometry, with coordination of azomethine nitrogen, phenolate oxygen, terminal amine of the thiosemicarbazone ligand and amine nitrogen of diethanolamine. The cytotoxic effects of the ligands and the complexes were evaluated against two different types of cancer cells (THP-1 human leukaemia monocytic cell line and MDA-MB-231 aggressive breast cancer cell line) and healthy cells (HUVEC human umbilical vein endothelial cell line) by using the MTT method. The findings demonstrated that the chloro-derivatives exhibited better efficacy compared to cisplatin in targeting the monocytic leukemia cell line while displaying reduced toxicity towards healthy cells.