Synthesis, spectral, DFT calculations and antibacterial studies of Fe(III) complexes of new fluorescent Schiff bases derived from imidazo[4',5':3,4]benzo[1,2‐<i>c</i>]isoxazole

Abstract

New fluorescent heterocyclic ligands were synthesized by the reaction of 8‐(4‐chlorophenyl)‐3‐alkyl‐3 H ‐imidazo[4',5':3,4]benzo [1,2‐ c ]isoxazol‐5‐amine with p ‐hydroxybenzaldehyde and p ‐chlorobenzaldehyde in good yields. The coordination ability of the ligands with Fe 3+ ion was examined in an aqueous metanolic solution. Schiff base ligands and their metal complexes were characterized by elemental analyses, IR, UV–vis, mass, and NMR spectra. The optical properties of the compounds were investigated and the results showed that the fluorescence of all compounds is intense and their obtained emission quantum yields are around 0.15 – 0.53. Optimized geometries and assignment of the IR bands and NMR chemical shifts of the new complexes were also computed by using density functional theory (DFT) methods. The DFT‐calculated vibrational wavenumbers and NMR chemical shifts are in good agreement with the experimental values, confirming suitability of the optimized geometries for Fe(III) complexes. Also, the 3D‐distribution map for HOMO and LUMO of the compounds were obtained. The new compounds showed potent antibacterial activity and their antibacterial activity (MIC) against Gram‐positive and Gram‐negative bacterial species were also determined . Results of antibacterial test revealed that coordination of ligands to Fe(III) leads to improvement in the antibacterial activity.