Thione-Based Nickel(II) Complexes as Functional Antioxidant Mimics: Scavenging Activity of Reactive Oxygen Species O2 −· and X-Ray Crystal Structure of [Ni(Ttxyly)2]2 {Ttxylyl = Hydrotris(2-mercapto-1-xylyl-imidazolyl)borate}

Two new thione-based nickel complexes, viz., [Ni(Tmipr)2Cl2]⋅2H2O 1 and [Ni(Ttxyly)2] ⋅H2O⋅2CH3OH 2 {Tmipr = 1-(2-isopropylphenyl)-1H-imidazole-2(3H)-thione; Ttxylyl− = hydrotris[1-(2,6-dimethylphenyl)-1H-imidazole-2(3H)-thione]borate anion} have been synthesized. Their structures and properties were characterized by several physicochemical methods, namely elemental and thermal analysis, FT-IR and Raman and UV–Vis spectroscopes, as well as electrical molar conductivity measurements. Structural determination of complex 2 showed that the coordination geometry around nickel atom is distorted tetrahedral with four thione sulfur donors from two molecules of the ligand KTtxylyl. Steric interactions between the xylyl rings appear to be responsible for the formation of the mononuclear nickel(II) complex 2. Molecules of complex 2 are connected via S–H···O hydrogen bonds, involving hydrogen atoms of the coordinated thiones and lattice water molecules. The superoxide dismutase biomimetic catalytic activities of both complexes were tested and found to be promising candidates as functional mimic enzyme to serve for complete superoxide radical’s detoxification. The observed IC50 values of these complexes are 8.38 and 7.4 mM for complexes 1 and 2, respectively.