Polymeric zinc complexes with 2,2′-dipyridylamine and different benzenepolycarboxylato ligands: Synthesis, structure, characterization and antimicrobial activity

Abstract

A series of new zinc complexes containing the 2,2′-dipyridylamine (dipya) ligand and anions of four benzenepolycarboxylic (BPC) acids, namely phthalic (H2pht), isophthalic (H2ipht), terephthalic (H2tpht) and pyromellitic (H4pyr), have been synthesized by ligand exchange reactions. The complexes were characterized based on elemental analysis, FTIR spectroscopy and thermal (TG/DSC) analysis. The complexes were found to have the formulae [Zn(dipya)(pht)] (1), [Zn(dipya)(ipht)]n (2), {[Zn(dipya)(tpht)]·H2O}n (3) and [Zn2(dipya)2(pyr)] (4). Compounds 2 and 3 have been obtained as single crystals and their crystal structures were determined from X-ray diffraction data. In both structures the coordination number of the Zn atoms is five and they are linked by bridging BPC ligands. In 2, the ipht ligand is coordinated in a tridentate manner via chelate and monodentate COO groups, whereas two crystallographically different tpht ligands in 3 are coordinated as bis-chelate and bis-monodentate ligands, respectively. These combined modes of ipht and tpht anions resulted in zigzag chains of 2 and 3. Two-dimensional pseudo-layers in 2 and a three-dimensional network in 3 are governed by hydrogen bonds and C–H⋯O interactions which are formed between the zigzag chains, and by additional C–H⋯π interactions in 3. The antimicrobial activity of complexes 1–4 was screened in vitro against some Gram-positive bacteria (Bacillus subtilis, Enterococcus faecalis, Listeria monocytogenes and Staphylococcus aureus), some Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa and Salmonella enteritidis) and yeast Candida albicans. Complex 2 showed the most potent inhibitory effect against the tested microorganisms.