Green Synthesis Of Bio-Active Oxygen-Bridged Complexes: A Comparative Study Of Their Antioxidant And Antibacterial Potency

Abstract

Oxygen-bridged metal complexes show unique electronic properties, structural versatility, and bioactivity and are increasingly being studied in bioinorganic chemistry. Conventional preparative methods usually involve the use of toxic solvents and chemical reductants, which often raise sustainability issues. Herein, we present the green synthesis approach of three μ-oxo bridged binuclear complexes of iron (III), copper (II), and zinc (II) / using aqueous extract of Azadirachta indica and Ocimum sanctum as biological-reducing and capping agents. The synthesized complexes were characterized by UV-Vis and FTIR spectroscopy and were screened for antioxidant activity using DPPH and ABTS radical scavenging assays and antibacterial activity against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa via the agar well diffusion method. The copper-based [Cu–O–Cu] complex showed the highest antioxidant activity (IC50 36.2 μg/mL by DPPH; 31.8 μg/mL by ABTS), and the largest inhibition zones among all tested bacterial strains, with the highest activity against S. aureus (21.7 mm). The iron-containing [Fe–O–Fe] complex showed an intermediate yet stable antioxidant and antibacterial performance; while [Zn–O–Zn], had the poorest activity profile. These results not only establish a distinct order of bioactivity (Cu > Fe > Zn) but also indicate that the phytochemical-mediated synthesis produces oxygen-bridged complexes, which possess recognized therapeutic activity as well as a significantly lower environmental impact.