Two-step synthesis, structure and adsorption property of a dynamic zinc phosphonocarboxylate framework

Abstract

Two zinc phosphonocarboxylate frameworks, Zn_1.5(pbc)(2,2′-bpy) (1) (2,2′-bpy = 2,2′-bipyridine) and Zn(pbc)(NH₂(CH₃)₂)_0.5·0.5H₃O (2), were synthesized in a mixed-solvothermal condition. Their structures have been determined by single-crystal X-ray diffraction analysis, IR spectra and thermogravimetric analysis. Compound 1 is a three-dimensional zinc phosphonocarboxylate with auxiliary ligand of 2,2′-bpy. 2 was obtained by reheating the filtrate of 1 and shows a nanoporous open-framework with zeolitic GIS topology. At room temperature, 2 can absorb organic amine and solvents in its channels, causing a breathing effect and shrinkage of the pores, resulting in single-crystal-to-single-crystal transformation to structure 2a, Zn(pbc)(NH₂(CH₃)₂)·0.5DMF·2H₂O. The porosity of 2 was demonstrated by the methanol and water adsorption experiments, indicating selective guest uptake.