Synthesis, Characterization, Biological and Computational Insights of some Binuclear Azo Dye-Based Metal Complexes

Abstract

A novel family of binuclear transition metal complexes was synthesized with M = Zinc (II), Cobalt (II), Nickel (II), Copper (II), and Manganese (II). These complexes, formulated as [M₂(L)Cl₂(H₂O)₆] and [M′₂(L)Cl₂(H₂O)₂], were prepared using (E)-2,4-dihydroxy-5-((3-hydroxyphenyl)diazenyl)benzoic acid (LH₂), a newly synthesized pentadentate/hexadentate azo dye ligand. Their coordination patterns and structural features were systematically investigated using a wide range of spectroscopic and analytical techniques, including Fourier Transform Infrared (FTIR) spectroscopy, UV–Vis spectroscopy, magnetic susceptibility measurements, elemental analysis, thermal studies (TGA/DTA), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis. An octahedral geometry surrounding the metal centers was confirmed by magnetic and spectroscopic evidence. XRD patterns indicated a hexagonal structure for the ligand and a cubic structure for the Cobalt (II) complex, with nanocrystalline sizes of ~20–29 nm. The complexes' electronic structures, frontier molecular orbitals (HOMO–LUMO gap), molecular electrostatic potential (MEP), optical responses, and ideal geometries were all investigated using Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) computations. Both metal-to-ligand (MLCT) and ligand-to-metal (LMCT) charge-transfer transitions were visible in the simulated TD-DFT spectra. While HOMO-LUMO gaps ranged from 1.76 to 3.12 eV, suggesting varied reactivity across complexes. ESR spectroscopy of the Copper (II) complex indicated strong metal–ligand covalency and confirmed a binuclear configuration. Biological screening showed enhanced antibacterial activity for all complexes, especially against Pseudomonas aeruginosa. Antioxidant studies revealed the Ni (II) complex as the most potent (IC₅₀ ≈ 26.9 μM). Cytotoxicity assays (SRB) on MCF-7 cells showed that the Ni (II) complex exhibited the highest activity (IC₅₀ = 6.33 μM), comparable to doxorubicin (5.15 μM), followed by LH₂ (22.97 μM) C,o (II) (44.28 μM), Zn (II) (59.41 μM), and Cu (II) (78.87 μM). Molecular docking with EGFR, HER2, and 1MBB confirmed strong binding, supported by QSAR and ADMET profiles suggesting drug-likeness and low toxicity. These results highlight their therapeutic and optoelectronic potential.