Coordination complexes constructed from pyrazole–acetamide and pyrazole–quinoxaline: effect of hydrogen bonding on the self-assembly process and antibacterial activity

Abstract

Two mononuclear coordination complexes of N-(2-aminophenyl)-2-(5-methyl-1H-pyrazol-3-yl)acetamide (L₁), namely [Cd(L₁)₂Cl₂] (C₁) and [Cu(L₁)₂(C₂H₅OH)₂](NO₃)₂ (C₂) and one mononuclear complex [Fe(L₂)₂(H₂O)₂](NO₃)₂·2H₂O (C₃), obtained after in situ oxidation of L₁, have been synthesized and characterized spectroscopically. As revealed by single-crystal X-ray diffraction, each coordination sphere made of two heterocycles is completed either by two chloride anions (in C₁), two ethanol molecules (in C₂) or two water molecules (in C₃). The crystal packing analysis of C₁, C₂ and C₃, revealed 1D and 2D supramolecular architectures, respectively, via various hydrogen bonding interactions, which are discussed in detail. Furthermore, evaluation in vitro of the ligands and their metal complexes for their antibacterial activity against Escherichia coli (ATCC 4157), Pseudomonas aeruginosa (ATCC 27853), Staphylococcus aureus (ATCC 25923) and Streptococcus fasciens (ATCC 29212) strains of bacteria, revealed outstanding results compared to chloramphenicol, a well-known antibiotic, with a normalized minimum inhibitory concentration as low as 5 μg mL⁻¹.