Abstract:Complexes were prepared using prepared ligand  (E)-2-[(4-chlorophenyl)imino]methylphenol, by condensation and its interaction with Cu (II), Co (II), Ni (II), and Zn (II) ions. Prepared such complexes were characterized by Spectroscopic techniques using ATR-FTIR, UV–visible, 1Ĥ NMR, AAS, SEM, EDAX, and thermalanalysis, including TGA, DTG, and DTA. Spectral data confirmed bidentate coordination through azomethine nitrogen and phenolic oxygen. Thermal studies revealed a multi-step decomposition process, with final residues corresponding to the respective metal oxides. SEM images showed distinct morphologies ranging from rod-like Cu (II) crystals to cauliflower-type Ni (II) aggregates, while EDAX and AAS confirmed metal incorporation. Antimicrobial studies against Escherichia coli, Staphylococcus aureus, Aspergillus niger, and Alternaria alternata revealed selective activity for the ligand and Cu (II) complex, whereas Co (II), Ni (II), and Zn (II) complexes were largely inactive. Chelate stabilization, poor solubility, bulky coordination geometries, and lack of redox activity rationalize the limited activity of most complexes. The Correlation of structural, thermal, and biological data establishes that metal identity and electronic properties critically govern antimicrobial performance.

Keywords:Schiff base ligand, Transition metal complexes, Spectral characterization, Thermal analysis, SEM–EDAX, Antimicrobial activity, Structure–activity relationship, Copper(II) complex.