Preparation, crystal structures, spectroscopic and thermal analyses of two co-crystals of [M(H2O)6][M(dipic)2] and (atrH)2[M(dipic)2] (M = Zn, Ni, dipic = dipicolinate; atr=3-amino-1H-1,2,4-triazole) with isostructural crystal systems

Treatment of an aqueous solution of dipicolinic acid (dipicH(2)) and 3-amino-1H-1,2,4-triazole (atr) with ZnCl2 or Ni(NO3)(2)center dot 6H(2)O (in a molar ratio of 1:1:1) led to the formation of co-crystals of (atrH)(2)[M(dipic)(2)]center dot[M(H2O)(6)][M(dipic)(2)]center dot 2H(2)O (M = Zn (1) and Ni (2)). Both complexes were characterized by elemental analysis, IR and UV-Vis spectroscopy. Their molecular and crystal structures were determined by Xray crystal structure analysis and their thermal stability was confirmed by TGA-DTA methods. The complexes 1 and 2 display isostructural features and crystallize in the triclinic P (1) over bar space group. The infrared spectra of 1 and 2 are very similar, so these complexes cannot be unambiguously distinguished by IR spectroscopy. Thermal methods confirm the number of co-crystallized water molecules in both compounds. Extensive hydrogen bonding interactions involving all aqua ligands, dipicolinate oxygen atoms and lattice water molecules further stabilize the complex units by linking them to form three dimensional polymeric networks. (C) 2011 Elsevier Ltd. All rights reserved.