Supramolecularly assembled pentameric and octameric water clusters stabilized by a mixed complex of Ni(II)

Abstract

Pyridine-2,4,6-tricarboxylic acid (ptcH₃) reacts with Ni(NO₃)₂ · 6H₂O and 2,2'-bipyridyl (bpy) in 2:2:1 molar ratio to form green crystals with the empirical formula, {[Ni(ptcH)₂][Ni(bpy)(H₂O)₄]6H₂O} (1). Water molecules present are associated to form discrete pentameric and octameric clusters which form an intricate array of H-bonding interactions with carboxylate O atoms, leading to a H-bonded 3D open framework structure. The water octamer takes the shape of a hexameric chair to which two water molecules are attached at one and four positions, while the pentameric structure is linear. Both these structures are unprecedented and their shapes are commensurate with the overall structure of the complex. Thermal analysis, X-ray powder diffraction and X-ray structural analysis have been used to characterize this compound.