Pyrazolone-derived transition metal(II) complexes as anti-fungal agents: design, structural insights and DFT modeling

A pyrazolone-containing azo ligand and its corresponding 1:2 complexes with Cu(II), Cr(II), Ni(II), Fe(II), and Co(II) metal ions were synthesized. The structure of the ligand was verified by 1H-NMR, 13 C-NMR, FT-IR, UV-visible spectroscopy, and HRMS. The complexes were evaluated by FT-IR, HRMS, elemental analysis, and electronic spectrum analysis. Analytical, spectroscopic, and computational results verified metal complexation via azo nitrogen and enolic oxygen donor atoms, resulting in stable metal complexes with a 1:2 metal-to-ligand stoichiometry. Density functional theory (DFT) simulations revealed successful ligand-to-metal charge transfer and electron delocalization during complexation, as evidenced by the complexes’ reduced HOMO-LUMO energy gaps compared to the ligands. Thermogravimetric Analysis (TGA) demonstrated the complexes’ excellent thermal stability by displaying progressive breakdown behavior. Furthermore, the synthesized compounds were subjected to in vitro antifungal activity against Candida albicans and Aspergillus niger. The Cu(II) and Co(II) complexes showed better effectiveness against C. albicans, with a MIC value of 250 μg/mL.