Synthesis and characterization of a new aroylhydrazone ligand and its cobalt(III) complexes: X-ray crystallography and in vitro evaluation of antibacterial and antifungal activities

Abstract

A new aroylhydrazone ligand, 2-benzoylpyridine-4-methoxybenzhydrazone (BPMBH) and its two cobalt(III) complexes, [Co(BPMB)2]NO3·1.5H2O (1) and [Co(BPMB)2]Cl·2H2O (2) have been synthesized and structurally characterized. The synthesized compounds are physico-chemically characterized by CHN analysis, molar conductivity, magnetic susceptibility measurements and spectroscopic techniques like MS, IR, UV and NMR. The high molar conductivity values of the complexes confirmed the presence of counter ions in the lattice of the cationic complexes. The molecular structure of the aroylhydrazone and its complexes have been resolved using single crystal XRD studies. In the solid state, the aroylhydrazone exists in the amido form as evident from the IR and XRD studies. The tridentate nature of the NNO donor aroylhydrazone was also confirmed from the IR spectral studies. XRD studies reveal that in all complexes, the tridentate aroylhydrazone coordinates to the Co(III) center via pyridine nitrogen, azomethine nitrogen and iminolate oxygen and found to possess distorted octahedral geometry. The complexes are bis-ligated cationic complexes in which chloride and nitrate ions act as counter ions. The antibacterial and antifungal activities of the aroylhydrazone and its Co(III) complexes have been screened against bacterial species Staphylococcus aureus, Enterobacter aerogenes, Bacillus subtilis, Streptococcus pyogenes, Klebsiella pneumonia, Salmonella typhi and Escherichia coli. The antifungal activity was also checked using fungi Aspergillus niger, Penicillium chrysogenum and Rhizopus oryzae. From the activity data we can infer that the metal complexes have better biological activity than the metal free ligand against the bacterial and fungal species which were tested.