Synthesis, characterization and antioxidative capacity of nickel(II) and zinc(II) complexes with 4-methylpyrazole

Two novel complexes of 4-methylpyrazole (L) were synthesized with Ni(II) and Zn(II). The crystal and molecular structures of the compounds were determined by single-crystal X-ray diffraction. The thermally more stable Ni(II) complex shows less antioxidative capacity, but the less stable Zn(II) complex higher antioxidative capacity. [Display omitted] •4-methylpyrazole is used in the case of poisoning with ethylene glycol or ethanol.•Synthesis of new complexes of Ni(II) and Zn(II) with 4-methylpyrazole.•Structure determination.•The thermal stability of Ni(II) complex is higher and of Zn(II) complex is lower.•The antioxidative capacity Ni(II) complex is lower and of Zn(II) complex is higher. In this paper, the coordination of 4-methylpyrazole (L) to Ni(II) and Zn(II) ions is studied through the reactions of Ni(OAc)2·4H2O and Zn(OAc)2·2H₂O with 4-methylpyrazole in a 1:2 metal-to-ligand molar ratio in ethanol at room temperature. From the reaction mixtures, new complex compounds of formulae: [Ni(OAc)2L4] and [Zn(OAc)2L2] were crystallized. The crystal and molecular structure of the synthesized complexes were determined by single-crystal X-ray structure analysis. The coordination environment of Ni(II) in its complex is octahedral, while that of Zn(II) is tetrahedral. The compounds are characterized by IR spectra and elemental analysis. Their thermal stability, a crucial property, is analyzed by thermogravimetry. To get a better insight into the decomposition mechanism coupled TG-MS measurements were carried out, too. The tests of the antioxidative activity of the new complexes on DPPH radical showed that the Zn(II) complex is more effective than the Ni(II) complex.