Synthesis, Characterization and Elucidation of Antimicrobial Potency of Iron and Manganese Complexes of Condensates of Salicylaldehyde and 2-Hydroxy Aniline

This study sought to synthesize and characterize iron and manganese complexes of 2-Phenyliminomethylphenol (PMP) and 2,2-hydroxybenzylideneaminophenol (HAP) as well as their mixed ligand complexes, and to elucidate their antimicrobial potency against microbes. The PMP and HAP were synthesized by reacting aniline and 2-aminophenol with salicylaldehyde respectively. The preparation of the unmixed metal complexes were achieved by adding 0.29mmol 2-Phenyliminomethylphenol ligand into the appropriate metal salt in the one hand, and by adding 0.29mmol 2,2-hydroxybenzylideneaminophenol ligand into the appropriate metal salt in the other hand, while the mixed metal complexes were prepared by addition of equimolar amount of ligands of 2-Phenyliminomethylphenol and 2,2-hydroxybenzylideneaminophenol into the appropriate metal salt. The molecular structures of the ligand and their complexes were determined using GC-MS, FTIR, UV-Vis, 1HNMR, and X-Ray diffraction studies. The melting point and solubility of the synthesized ligands and complexes were determined using standard methods. All complexes and ligands were found to be soluble in dimethylsulfoxide (DMSO). Asymmetric octahedral geometry was observed for all complexes with PMP, HAP, and mixed ligands. A bidentate ligand is coordinated to metal ions through oxygen atoms of carbonyl groups and nitrogen atoms of two imine groups for the metal complexes. Except for the mixed ligand complex of Fe (II), the XRD pattern indicates that the ligand and metal complexes are crystalline with high crystallite size of 119.23nm to 638.67nm. The XRD results indicate the crystal formed by the ligands and their respective complexes are large. However, the ligands had higher size compared to the complexes formed, which could be due to the complexation reactions. X-ray diffractograms of the metal complexes investigated showed good intense peaks indicating high crystallinity except for mixed ligand (PMP+HAP) complexes of iron Fe(PMP+HAP).Cl2 with reduced and broadened peak indicating reduced crystallinity. The FTIR spectra of 2-Phenyliminomethylphenol (PMP) indicated absorbance at 1569.2 cm–1 suggesting the stretching C=C bond in the benzene rings, while absorptions recorded at 1613.9 cm–1 suggested the =C-N stretching in the benzene ring. The electronic spectra of the complexes formed showed energy absorbed in the ultraviolet/visible region produced changes in the electronic energy of the compound resulting from transition of valence electrons in the complexes. Antimicrobial screening were carried 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). The ligand of 2-PMP and 2,2-HAP showed partial inhibitory action on the clinical isolates of Gram Postive, Gram Negative and no inhibitory action on the Fungi while metal complexes of Mn(II) with both mixed and unmixed ligands showed either strong or stronger inhibition on the clinical isolates of Gram Positve, Gram Negative and Fungi isolates. The study concludes that the synthesized ligands and complexes are soluble in dimethylsulfoxide (DMSO) but solubility varied with respect to other solvents. Also, all the complexes were purely crystalline as revealed by the results, and exhibited inhibitory actions on Gram Positive bacteria, Gram Negative bacteria and Fungi species.