New complexes of 5-methyl-5-(4-nitrophenyl)-hydantoin (L) with HgX2 (X = Cl−, Br−, and I−) were synthesized and characterized by several means including Fourier-transform infrared (FT-IR), proton nuclear magnetic resonance (1H NMR), carbon nuclear magnetic resonance (13C NMR), mass, CHN, and Energy Dispersive X-ray analysis. The spectroscopic data verified the coordination of (L) to the Hg (II) metal centers from the oxygen atom of the carbonyl functional group. The resulting data show that the prepared complexes (1), (2), and (3) have a monodentate coordination mode to metal center and structures showing X-bridged dimers. The cytotoxicity of the prepared complexes was investigated against cancer cell lines including MCF-7 (breast), A549 (lung), and AGS (gastric) adenocarcinoma cells. The obtained data showed that complexes (1) and (2) represent a higher cytotoxic effect against the tested cells. Also, the antioxidant behavior study displayed notable antioxidant potencies for complexes (1) and (2) in comparison with ascorbic acid, as a standard. Also, for the theoretical study, density functional theory calculations at the BP86/def2-SVP level of theory were applied. The strength and nature of donor−acceptor bonds between (L) and Hg fragments in the system of [L → HgX2]2 were performed by the use of the natural bond orbital analysis, energy decomposition analysis, and their natural orbitals for chemical valence variation. © 2021 The Chemical Society Located in Taipei & Wiley-VCH GmbH.
