SYNTHESIS AND CHARACTERIZATION OF COORDINATION COMPLEXES DERIVED FROM A CARBAZOLE-BASED SCHIFF BASE LIGAND WITH TRANSITION METALS AND ZINC, AND EVALUATION OF THEIR BIOLOGICAL ACTIVITY

A new Schiff base ligand obtained from carbazole was synthesized and structurally characterized. Its coordination complexes with Co (II), Ni (II), Cu (II), and Zn (II) ions were prepared for the first time and investigated through various spectroscopic techniques, including ¹H-NMR, UV-Vis, and FT-IR. Density Functional Theory (DFT) estimations were also employed to study the electronic structures, stability, and optimized geometries of the ligand and its complexes. The Co (II) and Ni (II) complexes exhibited an octahedral geometry with a general formula of [M(L)₂Cl₂], while Cu (II) and Zn (II) formed either square planar or tetrahedral geometries, depending on the coordination environment. Analysis of spectral and computational data suggested that nitrogen and oxygen atoms in the ligand actively participated in metal coordination. In antibacterial testing, the synthesized metal complexes demonstrated enhanced inhibition against Klebsiella pneumoniae and Staphylococcus aureus compared to the uncoordinated ligand, suggesting that complexation improved antimicrobial activity. These findings highlight the novelty of the synthesized ligand–metal complexes and their potential in medicinal chemistry, particularly given their distinct structural and electronic characteristics.