Two new Cu(II) coordination complexes with 1,2-bis(pyridin-4-yl)ethane bridge-ligand: Synthesis, characterization and antimicrobial activity

A new proton transfer salt and its two Cu(II) complexes have been synthesized. They were characterized by elemental, spectral (1H, 13C NMR, AAS, FTIR and UV-VIS) and magnetic measurement. Additionally, single crystal X-ray diffraction techniques were applied to all complexes. The antimicrobial and antifungal activities of all compounds were examined. [Display omitted] From the reaction of pyridine-2,6-dicarboxylic acid (H2PDC) with 1,2-bis(pyridine-4-yl)ethane (BPE), a new proton transfer salt, 4,4′-(ethane-1,2-di-yl)bis(pyridin-1-ium) pyridine-2,6-dicarboxylate (H2BPE)2+(PDC)2- (1), has been obtained. Two copper complexes, [Cu6(PDC)6(BPE)3(H2O)4].3H2O (2) and [Cu2(PDC)2(BPE)(H2O)2].H2O (3), were also synthesized. The first one was obtained from the proton transfer salt at room temperature, and the second one was obtained with mixed-ligand under hydrothermal conditions. Spectral (1H, 13C NMR, FT–IR and UV–VIS) and elemental analysis were performed for the structural analysis of the proton transfer salt. In order to determine the structures of the complexes, X-ray crystallography, spectral (AAS, UV–VIS and FT–IR), magnetic moment measurements and elemental analyses were carried out. Except for the Cu1 and Cu1i centers, which have a distorted square-planar geometry in 2, single-crystal X-ray analyzes of 2 and 3 revealed that the copper centers (Cu2-Cu2i and Cu3-Cu3i for 2 and Cu1-Cu1i for 3) are five-coordinated and have a distorted square-pyramidal geometry. Antimicrobial evaluation of compounds (1–3) has been tested against Bacillus subtilis, Listeria monocytogenes (ATCC 7644), Enterococcus faecalis (ATCC 29212) (Gram positive), Staphylococcus aureus (NRRL B-767), Escherichia coli (ATCC 25922) (Gram negative), Pseudomonas aeruginosa (ATCC 27853) and Candida albicans (F89) (yeast) microorganisms. The Minimum Inhibitory Concentration (MIC) values of the new 1–3 were compared with the antibacterial reference compounds Levofloxacin Cefepime, Vancomycin and the antifungal compound Fluconazole.