Copper complexes of pyrazolone-based Schiff base ligands: Synthesis, crystal structures and antibacterial properties

Two new Cu(II) Schiff base complexes were synthesized and characterized. The corresponding NO type bidentate Schiff base ligands were synthesized from the condensation of 2,5-dimethylaniline (HL1) or 3,5-dimethylaniline (HL2) with 4-acetyl-3-methyl-1-phenyl-5-pyrazolone. Another bidentate Schiff base ligand (HL3) was also synthesized from the condensation of Prop-2-en-1-amine (allylamine) with 4-acetyl-3-methyl-1-phenyl-5-pyrazolone but all attempts to synthesize the corresponding Schiff base complex failed. The ligands and complexes were characterized by general spectroscopic techniques including (HNMR)-H-1, IR, UV-Vis spectroscopy as well as elemental analysis. Crystal structure of one of the complexes, [Cu(L-1)(2)] was determined. Antibacterial potential of these ligands and complexes were tested against four bacteria, namely Escherichia coli (G(-)), Pseudomonas aeruginosa (G(-)), Staphylococcus aureus (G(+)) and Bacillus subtilis (G(+)). The ligands and complexes showed considerable antibacterial activity against both gram-positive and gram-negative bacteria. The ligands almost showed higher antibacterial activity than the corresponding complexes. (C) 2019 Elsevier B.V. All rights reserved.