Synthesis, characterization, antimicrobial, and corrosion inhibition studies of divalent complexes of 2-((5-chloro-2-hydroxyphenyl) amino) naphthalene-1,4-dione chelator

Abstract

Divalent metal complexes of 2-((5-chloro-2-hydroxyphenyl)amino)naphthalene-1,4-dione were synthesized by reacting the ligand with acetate salts of Cu(II), Zn(II), Co(II), Mn(II), Ni(II), and Fe(II) ions. The ligand and its complexes were characterized using Fourier transform infrared (FTIR), UV–visible spectroscopy, and physicochemical measurements, while their antimicrobial and corrosion inhibition properties were also investigated. The FTIR spectrum of the free ligand exhibited a characteristic ν(C=N) band at 1645 cm−1, which shifted to the 1621–1632 cm−1 region upon complexation, indicating coordination through the azomethine nitrogen atom. The appearance of new metal–ligand bands in the low-frequency region further supported complex formation. Electronic spectral studies suggested that the metal complexes predominantly adopt octahedral geometries, based on the observed ligand-centered and d–d electronic transitions. Solubility studies showed that the ligand and complexes were insoluble in water but generally soluble in dimethyl sulfoxide, while the zinc(II), iron(II) complexes, and the free ligand were only sparingly soluble in some organic solvents. The iron(II), cobalt(II), and zinc(II) complexes exhibited relatively high melting points (> 240 °C), indicating enhanced thermal stability. Antimicrobial screening revealed that the Cu(II) complex showed notable antibacterial activity against Bacillus sp. and Staphylococcus aureus, while appreciable antifungal activity was observed against Aspergillus flavus and Rhizopus stolonifer. Corrosion inhibition studies showed that the ligand exhibited concentration- and time-dependent inhibition, with a maximum efficiency of 69%. These findings highlight the potential of the synthesized complexes as multifunctional coordination compounds with promising biological and corrosion-protective applications.