Synthesis, crystal structure, theoretical calculation, spectroscopic and antibacterial activity studies of copper(II) complexes bearing bidentate Schiff base ligands derived from 4-aminoantipyrine: Influence of substitutions on antibacterial activity

Abstract A novel series of Cu(II) complexes, including: [Cu(L1)2]: C1, [Cu(L2)2]: C2, [Cu(L3)2]: C3, [Cu(L4)2]: C4, with four bis-N,O-bidentate Schiff base ligands (HL1: (E)-4-[(2‑hydroxy-3-methoxybenzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one; HL2: (E)-4-[(2‑hydroxy-4-methoxybenzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one; HL3: (E)-4-[(2‑hydroxy-5-methoxybenzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one; HL4: (E)-4-[(2‑hydroxy-6-methoxybenzylidene)amino]-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one have been synthesized and characterized by elemental analyses, FT-IR, 1H NMR and 13C NMR spectroscopic techniques. Furthermore, the crystal structures of HL4 and C2 were determined by single crystal X-ray analysis. Single crystal X-ray analyses, the structure of C2 confirmed the bidentate coordination mode. The metal center possesses a distorted tetrahedral geometry with bis-N,O donor atoms coordinating from Schiff base ligand. Theoretical calculation of the synthesized compounds were carried out by DFT using B3LYP method with employing the Def2-SVPD (for ligands) and Def2-SV(P) (for complexes) basis sets. Calculated data are in good accordance with the experimental investigations. The in vitro biological activities of the synthesized ligands and their copper(II) complexes were evaluated against Staphylococcus aureus and Escherichia coli. The activity data showed that the metal complexes have a promising biological potential comparable with the parent Schiff base ligands against bacterial species.