Synthesis, characterization, DFT, non-covalent interactions and antioxidant activity of N2O2-type template complexes of Zn(II)-derived from 5-ethoxy-2-hydroxy-acetophenone-S-methylthiosemicarbazone

Abstract

The N2O2-tetradentate Schiff-base complex of zinc(II) was synthesized by the template reaction of 5-ethoxy-2-hydroxy-acetophenone-S-methylthiosemicarbazone and 2-hydroxy-benzaldehyde (1)/2-hydroxy-4-methoxy-benzaldehyde (2). The compounds were characterized by elemental analysis, UV–visible, FT-IR, 1H NMR spectra, and thermogravimetric analyses. Antioxidant activities of the compounds were determined with Cupric Reducing Antioxidant Capacity and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays. The molecular geometries and vibrational frequencies were calculated using density functional theory (DFT/B3LYP) with the 6-311++G(d,p) basis set. The 1H NMR chemical shift values of the ligand and complexes in the ground state were calculated with the gauge-independent atomic orbital (GIAO) approach applying the same method and the basis set and compared with the experimental data. Using the TD-DFT method, electronic absorption spectra of the complexes were predicted at the same level. Also, the non-covalent interaction (NCI) plot index analysis reveals the presence of different kinds of non-covalent interactions in all complexes.