Architecture of zero-, one-, two- and three-dimensional structures based on metal ions and pyrazine-2,6-dicarboxylic acid

Six new complexes: [Ln2(pzda)3(H2O)2] · 2.5H2O (Ln = Nd, (1); Eu, (2)), [Co(pzda) (bpe)] · 0.125(bpe) · 1.75H2O (3), [Mn(pzda)(H2O)1.5] (4), [Co2(pzda)2(bpe)(H2O)4] · 0.5(CH3OH) · H2O (5) and [Co(pzda)(2,2′-bpy)(H2O)] · 0.5H2O (6) (H2pzda = pyrazine-2,6-dicarboxylic acid, bpe = 1,2-bis(4-pyridyl)ethane, 2,2′-bpy = 2,2′-bipyridine) were obtained from metal salts and H2pzda under hydro(solvo)thermal conditions. The single crystal X-ray structural analysis reveals that the title complexes have different structures, ranging from zero- to three- dimensions, which are mainly due to the different metal ions, and especially the coordination modes of the pzda ligands. Complexes 1 and 2 have 3D metal-organic frameworks containing a 1D tri-strand array, in which the pzda ligand adopts a pentadentate mode to link lanthanide ions. Complex 3 has a 2D metal-organic framework, in which the pzda ligand acts in a tetradentate mode to connect Co(II) ions into 1D chains, which are further connected by bpe spacers into a 2D framework. While in 4, both of the two carboxylate groups of the pzda ligand adopt μ2-O bridging modes to link Mn(II) ions into a 1D coordination polymer, which is further assembled into a 2D supramolecular network containing double-stranded hydrogen-bonded helical chains. In both 5 and 6, the pzda ligand binds metal ions as a tridentate ligand (ONO mode) to form zero dimensional structures. Complex 5 is a binuclear molecule, while 6 is a mononuclear complex, which can be attributed to the bridging ligand bpe for 5 and the terminal auxiliary ligand 2,2′-bpy for 6.

Graphical abstractMetal pyrazine-2,6-dicarboxylic acid complexes with zero-, one-, two- and three-dimensional structures were obtained by hydro(solvo)thermal reactions. The assembly of structural versatility for the title complexes shows that the metal ions and the coordination modes of the pzda ligand play an important role in the dimensions and thus the structures of the complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide