High-Capacity Iodine Adsorption and Nonporous to Porous Structural Transformation in an Originally Nonporous Coordination Polymer

Abstract

Pores are generally important for coordination polymers (CPs) to fulfill adsorption functions, while the high-capacity uptake of guest molecules by nonporous CPs is still very rare. Herein, we demonstrate an example of a nonporous Zn(II) CP, namely Zn-IPDA, that was assembled from Zn(II) and 4-(2,6-bis(4-(1H-imidazol-1-yl)phenyl)pyridin-4-yl)benzoic acid (H₂IPDA) and exhibited an unexpectedly high iodine vapour uptake capacity of 4.86 g g⁻¹. Although it was originally nonporous, it contained areas full of interaction sites for iodine attack, which can be seen as weaknesses of the crystal and are responsible for iodine adsorption. By combining DFT calculations, X-ray absorption fine structure (XAFS) spectra, and other experimental characterizations, iodine was found to attack the framework by changing the coordination environment of Zn(II) ions, causing framework amorphization and finally dispersing into the entire framework. In addition, the release of iodine from the high iodine-loaded Zn-IPDA induced a framework change from a crystalline nonporous to an amorphous porous stage, which showed an improved adsorption performance. This study demonstrates the possibility of obtaining porous CPs from nonporous precursors via the guest adsorption–desorption processes.