Synthesis, Spectral, Thermal Studies and Antimicrobial Evaluation of Transition Metal Complexes with Novel Schiff Base Ligand

Abstract

A novel coumarin Schiff base “(E)-7-hydroxy-4-methyl-8-(1-(1-(naphthalen-2-yl) ethylimino) ethyl)-2H-chromen-2-one” [HOMNEIEC] ligand was synthesized by the condensation of “8-acetyl-7-hydroxy-4-methyl-2H-chromen-2-one” [AHMC] with “1-(naphthalen-1-yl) ethylamine” [NEA]. The transition metal (II) ions complexes with this ligand were synthesized by a common method. The synthesized ligand and metal (II) complexes were studied using spectral (1H NMR, FTIR, Mass Spectrometry) and thermal (TGA) techniques for their structures. The 1H NMR and FTIR spectra of ligand confirm the formation of azomethine bond. The FTIR spectral data validated the formation of coordinate bond through phenolic oxygen on coumarin ring and nitrogen of azomethine with the metal ions. The m/z values in mass spectrum of ligand and its metal complexes were in agreement with their theoretical values of molecular/formula weights. The TGA thermograms suggested there are of two coordinated/lattice H2O molecules in each of the complex. The ligand and metal complexes were evaluated for their in vitro antimicrobial activities using broth microdilution method using DMSO solvent/diluent against Escherichia coli and Pseudomonas aeruginosa a gram-negative bacterial strain, Staphylococcus aureus and Streptococcus pyogenes a gram-positive bacterial strain, and Candida albicans, Aspergillus clavatus and Aspergillus niger a fungal strain. The metal complexes were found to have enhanced antimicrobial activities compare to the Schiff base ligand.