New heterocyclic Schiff base-metal complex: Synthesis, characterization, density functional theory study, and antimicrobial evaluation

A new series of heterocyclic Schiff base complexes derived from the condensation of nicotinohydrazide with different heterocyclic aldehyde, followed by metalation with Co (II) and Cu (II) metal ions. The chemical structures of the synthesized compounds have been characterized by elemental analysis, Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, ultraviolet-visible spectroscopy, and magnetic susceptibility. The spectral and magnetic data confirmed their chemical structures, furthermore, the geometry of Cu (II) and Co (II) complexes were square-planar or distorted tetrahedral. X-ray diffraction measurements supported the crystalline structures of the metal complexes rather than the amorphous form of the parent Schiff bases. Thermogravimetric analysis revealed the upgrading of the thermal stability of metal complexes compared to their Schiff base ligands. Antimicrobial efficacies of the Schiff base ligands and their corresponded metal complexes were screened against Staphylococcus aureus and Bacillus subtilis as Gram-positive bacteria, Escherichia coli, and Proteus vulgaris as Gram-negative bacteria, and fungi Aspergillus flavus, Candida albicans. The antimicrobial inhibitory data revealed higher antimicrobial activities of metal complexes compared to their Schiff base ligands. Density functional theory module by Gaussian 09 W software proved the chemical reactivity of the prepared Schiff base ligands based on the total energy, energy gap, E-HOMO, and E-LUMO energies.