Characterization, adsorption properties, metal ion-exchange and crystal-to-crystal transformation of Cd3[(Cd4Cl)3(BTT)8(H2O)12]2 framework, where BTT3-=1,3,5-benzenetristetrazolate

A new metal-organic framework, Cd-3[(Cd4Cl)(3)(BTT)(8)(H2O)(12)](2), was synthesized solvothermally in mixed DMF-H2O. It is constructed by chloride-centered [Cd4Cl](7+) square-planar units cross-linked by BTT3- ligands to form a porous sodalite-like anionic three-dimensional framework, with charge-balancing Cd2+ ions located inside cavities. It underwent single-crystal-to-single-crystal transmetalation with Co2+ or Ni2+ ions substituting nearly all the Cd2+ ions in both cavities and frameworks via ion-exchange processes. PXRD and TGA suggest the integrity and robustness of these crystals at 150 degrees C, and their single crystal structures were determined by X-ray diffraction techniques at both ambient temperature and 150 degrees C. The high-temperature X-ray analyses indicate that the metal ions in cavities migrate to bind the nitrogen atoms of tetrazolyl ligands upon the removal of solvent molecules. Gas adsorption studies gave large surface area and good H-2 storage capacities for these porous materials.