Synthesis, Spectroscopic, And Biological Investigation Of Metal Complexes With (1E,2E)-N-Hydroxy-1,2-Diphenyl-2-(2-Phenylhydrazinylidene) Ethanimine Ligand

A novel Schiff base ligand, (1E,2E)-N-hydroxy-1,2-diphenyl-2-(2-phenylhydrazinylidene)ethanimine (HSmSL1), was synthesized via condensation of 1,2-diphenyl-2-(2-phenylhydrazinylidene)ethanone with hydroxylamine hydrochloride and characterized as a pale yellow crystalline solid (m.p. 167–169°C) with a molecular formula of C15H14N2O. Its transition metal complexes with Fe(II), Co(II), Ni(II), Cu(II), Mn(II), Pd(II), Zn(II), Cd(II), and Hg(II) were prepared in a 2:1 ligand-to-metal ratio and characterized using UV-Vis, FTIR, NMR, and powder XRD. UV-vis spectroscopy revealed characteristic π-π∗ and ligand-to-metal charge transfer transitions, confirming square planar geometries, with d-d transitions at 540 nm (Fe), 490 nm (Co), and 610–626 nm (Ni). FTIR analysis indicated coordination through deprotonated oxygen and nitrogen atoms, evidenced by shifts in C=NN (1573–1598 cm−1) and C=NOH (1509–1538 cm−1) bands and new O-M (503–535 cm−1) and N→M (516–565 cm−1) vibrations. The 1H NMR spectrum of HSmSL1 showed -OH (12.367 ppm), -NH- (10.527 ppm), and aromatic (7.167–7.985 ppm) signals, while 13C NMR confirmed C=N (154.94 ppm), Ar C-NH (151.28 ppm), and Ar C-C (135.46 ppm) carbons. Powder XRD indicated an amorphous nature for the complexes, suggesting disordered molecular arrangements. Antimicrobial testing against Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Candida albicans, and Saccharomyces cerevisiae revealed superior activity for Ni(II), Cd(II), and Hg(II) complexes, with inhibition zones of 11–15 mm and 12–16 mm against bacteria and fungi, respectively, often matching or exceeding the standard (12–14 mm). Notably, the Zn(II) complex exhibited exceptional activity against P. aeruginosa (18 mm). The enhanced bioactivity of metal complexes over the ligand underscores the role of coordination in improving lipophilicity and microbial target interactions, highlighting their potential as novel antimicrobial agents, though toxicity concerns for Cd(II) and Hg(II) warrant further evaluation.