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.