Syntheses, crystal structures and antibacterial activities of six cobalt(II) pyrazole carboxylate complexes with helical character

Six new cobalt(II) complexes, [Co1.5(HL)3(H2O)3]·H2O (1), [Co(HL)2(2,2′-bipy)] (2), [Co(HL)2(phen)] (3), [Co(HL)2(H2O)2]·(4,4′-bipy) (4), [Co(L)(4,4′-bipy)(H2O)]·H2O (5) and [Co(L)(4,4′-bipy)0.5(H2O)]·1.5H2O (6), (H2L = 5-chloro-1-phenyl-1H-pyrazole-3,4-dicarboxylic acid; 2,2′-bipy = 2,2′-bipyridine; phen = 1,10-phenanthroline; 4,4′-bipy = 4,4′-bipyridine) have been synthesized and characterized. Complexes 1–4 exhibit monomeric structures, but with the help of hydrogen bonding interactions all extend into 3D supramolecular networks with double-, single-, single- and quadruple-stranded helical chains, respectively. Complex 5 displays a layer structure comprising two kinds of single-stranded helical chains, and complex 6 also exhibits a layer structure, however, this consists of double-stranded and meso-helical chains; the 2D structures of complexes 5 and 6 are further assembled into 3D and 2-fold interpenetrating 2D supramolecular networks through hydrogen bond interactions, respectively. The thermal stabilities of the title complexes have been discussed. Furthermore, the antibacterial activities of the title complexes against tested bacteria were studied and compared to the activities of free ligands.

Six new cobalt(II) complexes with 5-chloro-1-phenyl-1H-pyrazole-3,4-dicarboxylic acid and three kinds of N-donor co-ligands with diverse intriguing helical characters have been synthesized and characterized. The single crystal X-ray diffraction results demonstrate that the N-donor co-ligands, hydrogen bonds and bridging conformations of the carboxylate groups have significant influence on the helical structures of the title complexes.Figure optionsDownload as PowerPoint slideHighlights
► Six new Co(II) complexes with pyrazole carboxylic acid and N-donor co-ligands have been synthesized and characterized.
► The complexes show diverse intriguing helical characters.
► The helical characters depend on the N-donor co-ligands, hydrogen bonds, etc.
► Thermal stabilities of the title complexes are discussed.
► The complexes exhibit greater activity than the corresponding free ligand.