Synthesis, Characterization and Antimicrobial Analysis of Nickel and Cobalt Complexes of Condensates of Salicylaldehyde and 2-Hydroxy Aniline
Authors: S.E. Anumata , L.O. Ezenweke , E.N. Orjiako 
Published: September 2024

This study on the synthesis, characterization and antimicrobial analysis of Nickel and Cobalt complexes of condensates of salicylaldehyde and 2-hydroxy aniline constitutes an attempt towards the development of new molecular compounds that could destroy the barrier of resistance of pharmaceutical products. The ligands of 2-phenyliminomethylphenol (PMP) and 2,2-hydroxy benzylidene aminophenol (HAP) were first prepared by separately reacting Aniline with Salicylaldehyde on the one hand, and 2-aminophenol with Salicylaldehyde on the other hand. The unmixed metal complexes were prepared by reacting either of 0.29 mmol 2-phenylimino methyl phenol ligand with the metal salt or 0.29 mmol 2,2-hydroxybenzylideneaminophenol ligand with the metal salt while the mixed metal complexes were prepared by addition of equimolar amount of ligands of 2-phenyliminomethylphenol  and 2,2-hydroxybenzylideneaminophenol into the metal salt. The molecular structures of the ligands and their complexes have been determined and characterized using GC-MS, FTIR, UV-Vis, 1H-NMR, and X-ray diffraction techniques. The melting point and solubility of the ligands and synthesized complexes were equally determined. Antimicrobial studies were carried out with ligands PMP and HAP and the metal complexes using clinical isolates of Gram Positive Bacteria (Staphylococcus aureus and Bacillus substilis), Gram Negative Bacteria (Escherichia coli and Pseudomonas aeruginosa) and Fungi (Candida albicans and Aspergillus niger). All complexes and ligands were found to be soluble in dimethylsulfoxide (DMSO). Asymmetric Octahedral geometry is observed for Nickel (II) and Cobalt (II) complexes with PMP, HAP, and the mixed ligands. A bidentate ligand is coordinated to metal ions through oxygen atoms of carbonyl groups and nitrogen atoms of two imine groups for Nickel (II) and Cobalt (II) complexes. The findings from the XRD pattern indicate that the ligand and metal complexes are crystalline with a high crystallite size of 119.23nm to 638.67nm. The FTIR spectra for 2-phenyliminomethylphenol (PMP) showed IR absorption band at 1569.2 cm-1 suggesting the stretching vibration of the C=C bond in the benzene rings, while the bands at 1613.9 cm-1 indicated the =C-N stretching in the benzene ring. The complexes showed electronic spectra which suggest that energy was absorbed in the ultraviolet/visible region, producing changes in the electronic energy of the compound and resulting from the transition of valence electrons in the complexes. The XRD findings reveal that the crystal formed by the ligands and their respective complexes are large. The ligands were found to be larger in size than the complexes and this could be due to the complexation reactions. The X-ray diffractograms of the metal complexes produced good intense peaks that suggest high crystallinity. The ligand of 2-phenyliminomethylphenol (PMP) and 2,2-hydroxy benzylidene aminophenol (HAP) showed partial inhibitory action on the clinical isolates of Gram Postive, Gram Negative and zero inhibitory effect on the fungi while the divalent metal complexes of both mixed and unmixed ligands exhibited either stronger or strongest inhibition. The study concludes that the synthesized ligands and their metal complexes are purely crystalline as revealed by the chemical analysis, exhibited inhibitory actions on Gram Positive, Gram Negative and fungi species.