Synthesis, spectroscopic characterization, antioxidant and antimicrobial activities of Ni(II), Cu(II), Co(II), and Zn(II) complexes of the bidentate Schiff base 2-((4-(dimethylamino)benzylidene)amino)phenol

A bidentate Schiff base ligand, 2-((4-(dimethylamino)benzylidene)amino)phenol (L), was synthesized via the condensation of 2-aminophenol with 4-(dimethylamino)benzaldehyde and used to prepare Ni(II), Cu(II), Co(II), and Zn(II) complexes. The ligand and complexes were characterized by FT-IR, UV–Vis, 1H NMR, 13 C NMR, and ESI-MS spectroscopy. The spectroscopic data supported coordination through the azomethine nitrogen and phenolic oxygen donor atoms. Electronic spectra and conductivity measurements suggested square-planar geometries for the Cu(II) and Ni(II) complexes, tetrahedral geometry for the Zn(II) complex, and octahedral geometry for the Co(II) complex. Antioxidant activity was evaluated using the DPPH radical scavenging assay. The Cu(II) complex showed the strongest antioxidant activity, with an IC50 value of 82 ± 1 µg mL − 1, exhibiting higher activity than the free ligand and approaching that of the reference antioxidant. Antimicrobial activity was investigated against Gram-positive bacteria (Staphylococcus aureus and Listeria monocytogenes), Gram-negative bacteria (Escherichia coli and Salmonella enteritidis), and Candida glabrata. The Co(II) complex exhibited the most potent antimicrobial activity, showing the lowest MIC values, whereas the free ligand was particularly active against S. enteritidis. These results indicate that metal coordination can substantially influence the biological properties of Schiff base derivatives, highlighting the Cu(II) and Co(II) complexes as promising candidates for further investigation.