Synthesis, characterization, and evaluation of biological activities of M(II) metal complexes (M=Co, Zn and Cu) based on a bidentate Schiff base ligand 2-((4-nitrobenzylidene)amino)phenol

In this study, new Co(II), Zn(II), and Cu(II) complexes based on the Schiff base-type bidentate ligand 2-((4nitrobenzylidene)amino)phenol were synthesized and fully characterized by FT-IR, UV-Vis, NMR, ESI-MS, molar conductivity, and thermal analyses (DTA/TGA). Spectroscopic data confirmed coordination via azomethine nitrogen and phenolic oxygen, as well as a tetrahedral geometry for the Zn and Co complexes and a square planar geometry for the copper complex. Thermal analyses indicated high stability of the complexes. Biological evaluation revealed that all complexes exhibited increased antioxidant and antimicrobial activities compared to the free ligand. In particular, the Cu(II) complex showed the highest radical scavenging capacity with an IC₅₀ of 0.00592 mg/mL, surpassing ascorbic acid, while the Zn(II) and Co(II) complexes also showed significant activity. Antimicrobial tests demonstrated selective inhibition of Gram-positive bacteria (notably Staphylococcus aureus ATCC 25,923 and 6538) and enhanced antifungal activity against Candida albicans. These results highlight the potential of these Schiff base metal complexes as promising candidates for biomedical applications.