Microwave-assisted synthesis, spectral characterization and DFT studies of Zn(II) complexes based on N-acylhydrazone ligands: stability and antioxidant activity

This article reports the synthesis of seven Zn(II) complexes containing N-acylhydrazone ligands (L1 to L7) and the assessment of their antioxidant. Microwave assisted-synthesis of ligands with ZnCl₂ in MeOH yielded tetrahedral Zn(II) complexes with a 1:2 metal: ligand ratio, characterized by HRMS, FTIR, and UV-Vis spectroscopy, thermal and electrochemical analyses, and DFT calculations. The (L3)₂Zn complex exhibited the lowest thermal stability, and (L6)₂Zn and (L7)₂Zn were the most stable. XRD powder showed that all complexes have good crystallinity with crystalline dimensions ranging from 32 to 86 nm. Cyclic voltammetry of Zn(II) complexes indicated a reversible redox process for (L4)₂Zn and an irreversible process for the remaining six complexes: (L1)₂Zn to (L3)₂Zn and (L5)₂Zn to (L7)₂Zn. Antioxidant activity of ligands and complexes was assessed by the DPPH method; the L7 ligand and corresponding (L7)₂Zn complex exhibited good activity, IC₅₀ = 65.30 μmol.l^-1 and 78.70 μmol.l^-1, respectively, when compared with standard ascorbic acid.