Nickel(II) complex derived from 5-phenyl-1,3,4-oxadiazole 2-thiol and dppe ligands: synthesis, crystal structure, cytotoxicity and theoretical studies

In this study, the novel Ni(II) complex [Ni(N-L)(S-L)(dppe)], where L = 5-phenyl-1,3,4-oxadiazole-2-thiol (HL), was synthesised. The Ni(II) complex was characterised by FT-IR and UV-Vis spectroscopy, molar conductivity, and single-crystal X-ray diffraction. The complex crystallises in a monoclinic system (P21/c) with a distorted square-planar geometry. One HL ligand coordinates with the Ni(II) ion through sulphur in its thiol form, while the other HL ligand is ligated via the nitrogen atom in the thione form. The dppe ligand chelates Ni(II) via two phosphorus atoms forming a five-membered ring. The complex exhibits strong cytotoxicity against MCF7 (IC50 = 6.76 µg/mL) and A549 (IC50 = 8.07 µg/mL) cell lines. DFT results indicate that the synthesised nickel(II) complex is less thermodynamically stable than the free ligands, with a ΔE value of 3.4349 eV. Hirshfeld surface analysis was conducted to identify intermolecular interactions as the key contributors to crystal packing.