Synthesis, Characterization and Antimicrobial Studies on Mn (II), Co (II) and Ni (II) Complexes with Schiff base derived from o-phenylenediamine and 1-acetylnaphthalene

The Schiff base was obtained in high yield (81.34%) through the condensation of o-phenylenediamine and 1-acetylnaphthalene in a 1:2 molar ratio. The synthesized Schiff base was subsequently used to prepare Mn, Co, and Ni metal complexes. The ligand and its metal complexes were characterized using FT-IR, conductivity measurement, melting point/decomposition temperature, solubility test, magnetic susceptibility, UV-Visible spectral analysis, and elemental analysis. The ligand melted at 177°C, while the metal complexes decomposed at 200–208°C, indicating high thermal stability. The molar conductivity values of the complexes ranged from 30.40–44.40 Ω−1 cm2 mol−1, confirming their non-electrolytic nature. Magnetic susceptibility measurements showed that all the complexes were paramagnetic. The compounds were soluble in DMF and DMSO, insoluble in water, and slightly soluble in some common organic solvents. FT-IR analysis confirmed the coordination of the carbonyl oxygen to the metal centers in all the complexes. Hydration studies revealed that all the complexes contained water molecules predominantly as water of crystallization. The antimicrobial activities of the ligand and its complexes were evaluated against three bacterial isolates (Staphylococcus aureus, Bacillus subtilis, and Escherichia coli) and three fungal isolates (Candida albicans, Tinea pedis, and Tinea capitis). All compounds were active against the tested isolates, although activity decreased with decreasing concentration. The complexes showed higher antimicrobial activity than the corresponding ligand but lower activity than the standard. The ligand exhibited a lower IC50 value than the complexes, whereas the complexes had lower LC50 values than the ligand.