Theoretical and biological studies of new complexes with Schiff-Mannich ligand

The Schiff-Mannich base is derived from 1,3,4-thiadiazole, prepared by reacting 2-amino-5-mercapto-1,3,4-thiadiazole, p-bromobenzaldehyde, and 4-chloroaniline in the presence of formaldehyde. The discovered molecule is (E)–N–(4-bormobenzylidene)-5-((4-chlorophenylamino)methyltio) -1,3,4thiadiazol-2amine (L), which is coordinated with six metal ions: Cr(III), Mn(II), Zn(II), Pd(II), Pt(IV), and Au(III). The ligand was characterized using the following methods: Mass spectrum, 1H-NMR, 13C-NMR, FT-IR, UV-Vis, and C.H.N.S. The complexes were further evaluated using molar conductivity, magnetic susceptibility, and atomic absorption spectroscopy. The experimental results showed that the ligand coordinates with the metal ion in a tridentate manner. All generated ligands and complexes were tested for antifungal and antibacterial characteristics at a concentration of 0.02 M against one fungus and two bacteria (Gram-negative and Gram-positive). Using molar ratio methods, the M:L ratio was determined to be (1:1) at a concentration of 1x10-4 M. In addition, the prepared ligand and complexes in the gas phase were studied with the HyperChem 8.0.7 program. The program was used to determine the ligand's heat of formation (∆Hf0), binding energy (∆Eb0), HOMO and LUMO energies, electrostatic potential, and infrared vibrational frequencies. The current study discovered that the complexes were more stable than the ligand, and the practical and theoretical vibrational frequency results were consistent. KEY WORDS: 2-Amino-5-mercapto-1,3,4 thiadiazole, Biological study, Metal ions, Schiff-Mannich base, Theoretical study Bull. Chem. Soc. Ethiop. 2026, 40(2), 455-467 DOI: https://dx.doi.org/10.4314/bcse.v40i2.14