Preparation, structural diversity and characterization of a family of Cd(II)-organic frameworks

Two Cd(II)-organic frameworks based on 5-iodoisophthalate (IIP2-), {[Cd(IIP)(bte)(H2O)]center dot H2O}(n) (1) and [Cd(IIP)(bpp)(H2O)](n) (2), were obtained either at an ambient temperature or under solvothermal conditions at 120 degrees C in the presence of 1,4-bis(1,2,4-triazol-1-yl) ethane (bte) and 1,3-bis(4-pyridyl) propane (bpp) as auxiliary ligands, respectively. 1 is a novel discrete single-walled Cd(II)-organic tube (SWCOT) which further extends into a 3D supramolecular interdigitated microporous columnar architecture supported by C-I center dot center dot center dot I halogen bonds and hydrogen bonds, while 2 exhibits an interesting two-fold interpenetrated 3D diamond network architecture. When the auxiliary ligands bte or bpp were replaced by a longer spacer ligand with more flexibility, 1,4-bis(triazol-1-ylmethyl) benzene (bbtz), the unique discrete single-walled Cd(II)-organic nanotube (SWCONT), {[Cd(IIP)(bbtz)(H2O)]center dot H2O}(n) (3), which further extends into a 3D supramolecular microporous framework supported by face-to-face pi...pi stacking interactions and hydrogen bonds, was generated at room temperature. Under solvothermal conditions at 120 degrees C, an interesting two-fold 2D embracing (4,4) topological network, [Cd(IIP)(bbtz)(H2O)] (4), which further extends into a two-fold 3D embracing supramolecular framework through O-H center dot center dot center dot O hydrogen bonds, is obtained. 4 loses crystallinity in air, leading to the formation of [Cd(IIP)(bbtz)]center dot 0.5H(2)O (4A) evidenced by elemental analysis, thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD). Remarkably, in situ rapid and reversible dehydration-rehydration in static air occurs in 1-3, indicating their potential applications as water absorbent and sensing materials. Dehydrated 1 and 3 show selective gas adsorption of CO2 over N-2 and dehydrated 3 can adsorb methanol and ethanol vapors strongly. These compounds exhibit blue fluorescence in the solid state.