Synthesis, structural characterization and properties of one-dimensional coordination polymers of cobalt(II)- and nickel(II)-phosphonate complexes with 2,2′-bipyridine as a secondary ligand component: Observation of both cis and trans conformations of a d

Two new isomorphous cobalt and nickel phosphonates [MII(2,2′-bipy)2LH4]n[LH2]n, M = Co (compound 1), M = Ni (compound 2) were hydrothermally synthesized from p-xylylenediphosphonic acid (LH4) and the corresponding metal salts with 2,2′-bipyridine as secondary ligand component. Both the compounds 1 and 2 are characterized by routine elemental analyses, IR-, electronic-spectral analyses, thermogravimetric studies and unambiguously characterized by single crystal X-ray crystallography. The structures were refined in monoclinic space group C2/c. The crystal structure consists of 1D [M(2,2′-bipy)2LH4]2+ chains and [LH2]2− anions. The flexibility of non-rigid ligand p-xylylenediphosphonic acid (LH4) tends to adopt a rare cis conformation in the crystal structure to meet the coordination requirement of the metal center from the usual trans conformation. The hydrogen bonding in the crystal structure leads to cylindrical tubes that extend via p-xylylenediphosphonic acid resulting in a 2D supramolecular sheet throughout the crystal. Compounds 1 and 2 are additionally characterized by thermogravimetric studies.

Graphical abstractTwo new isostructural cobalt and nickel phosphonates [MII(2,2′-bipy)2LH4]n[LH2]n, M = Co (compound 1), M = Ni (compound 2) were hydrothermally synthesized from p-xylylenediphosphonic acid (LH4) and the corresponding metal salts with 2,2′-bipyridine as secondary ligand component. X-ray crystallography shows that both the compounds consist of 1D [M(2,2′-bipy)2LH4]2+ chains and [LH2]2− anions in which LH4 adopts a cis conformation during its coordination to the metal center. The corresponding trans conformation is observed in the anionic form [LH2]2−. The hydrogen bonding in the crystal structure leads to cylindrical tubes extended via p-xylylenediphosphonic acid resulting in a 2D supramolecular sheet.Figure optionsDownload full-size imageDownload as PowerPoint slide