Syntheses and crystal structures of two new nickel (II) metal-organic frameworks with a polydentate ligand

Two metal-organic frameworks {Na-2[Ni(L)(2)(H2O)]}(n) (1) and {[Ni(L)(H2O)]center dot 2H(2)O}(n) (2) (H2L = N-pyrazinesulfonyl-glycine) have been prepared by reaction of the same proportion Ni(CH3COO)(2)center dot 4H(2)O and H2L but with different pH values in water-ethanol mixed solution, and were characterized by X-ray diffraction, elemental analysis, IR spectrum. X-ray analysis indicates that 1 is a 3-D polymeric structure containing two different secondary building units (SBUs, NiN4O2 and Na2O8), in which two deprotonated L ligands coordinate in a facial tridentate arrangement about the Ni-II atom. While complex 2 is a 1-D chain structure, in which three N atoms of two L ligands coordinate to one Ni-II atom but its pyrazyl N atom monodentate-bridge to adjacent Ni-II atom. Thus SBUs Ni(L)(H2O)(2) are obtained between two neighboring Ni-II atoms and they connect one another to form this new polymer. In the crystal, two different hydrogen bond motifs and pi center dot center dot center dot pi stacking are found in 1 and 2.