Two flexible zinc–triazole–dicarboxylate frameworks: breathing behaviors for CO2 uptake and dye adsorption properties

Abstract

Two new zinc-triazole-carboxylate frameworks, namely [(CH₃)₂NH₂][Zn₂(DMTDC)₂(tz)]·3DMF·5H₂O (1) and [Zn₂(DMTDC)(tz)₂]·DMF·2H₂O (2, H₂DMTDC = 3,4-dimethylthieno [2,3-b]-thiophene-2,5-dicarboxylic acid, Htz = 1,2,4-triazole), were synthesized by using a thiophene-containing dicarboxylate and two different triazole ligands. In compound 1, the tz ligand is in situ generated from the deamination of 4-atz (4-atz = 4-amino-1,2,4-triazole) under solvothermal conditions. Single-crystal X-ray diffraction analyses show that compound 1 is a 3D anionic porous framework based on dinuclear Zn(II) tetracarboxylate paddlewheel SBUs and dinuclear [Zn₂(tz)₂] subunits whereas 2 is a neutral 3D framework and a pillared-layer structure based on the Zn–triazolate layers and dicarboxylate pillars. Both of the frameworks can be considered as pcu α-Po topologies, and exhibit irreversible solid-state structural transformations upon solvent removal/uptake. Gas adsorption experiments reveal that the two compounds display CO₂-induced, gate-opening adsorption isotherms at 195 K. Dye adsorption tests indicate that compound 1 can selectively adsorb cationic dyes over the anionic and neutral dyes whereas 2 hardly adsorbs any selected dyes.