Ni(II) and Cu(II) complexes of pyridine-carboxamide Schiff base: Synthesis, characterization, and antioxidant activities evaluation

This research introduces two novel Schiff base complexes: [LNi(H2O)2]H2O and [LCu]3H2O, where L represents (E)-2-(5-bromo-2-hidroksibenzilidenamino)-6-metil-4,5,6,7-tetrahidrotiyeno[2,3-c]piridin-3-karboksamid. These complexes were synthesized by reacting of Schiff base ligand (L) containing ON donor atoms with an equimolar amount of NiCl2∙6H2O and Cu(NO3)2∙3H2O salts. The compounds were extensively characterized using various analytical and spectroscopic techniques, including elemental analysis, FT-IR, 1H-NMR, 13C-NMR, UV-Vis spectroscopy, mass spectrometry, magnetic susceptibility measurements, molar conductivity, and thermogravimetric analysis. Additionally, the antioxidant properties of both the ligand and complexes were evaluated in vitro using three methods: DPPH free radical scavenging activity, ABTS+ cation radical scavenging activity, and CUPRAC reducing power. From the analytical data, it was observed that the Ni(II) complex has an octahedral structure and the Cu(II) complex has a square planar structure. The antioxidant activity results indicated that some of the complex compounds demonstrated superior antioxidant effects compared to the Schiff base ligand.