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

Abstract

A new metal–organic framework, Cd₃[(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 °C, and their single crystal structures were determined by X-ray diffraction techniques at both ambient temperature and 150 °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 H₂ storage capacities for these porous materials.