Lock-and-Key and Shape-Memory Effects in an Unconventional Synthetic Path to Magnesium Metal-Organic Frameworks

We report a new magnesium metal-organic framework (MOF) (CPM-107) with a special interaction with CO₂ . CPM-107 contains Mg₂ -acetate chains crosslinked into a 3D net by terephthalate. It has an anionic framework encapsulating ordered extra-framework cations and solvent molecules. The desolvated form is closed and unresponsive to common gasses, such as N₂ , H₂ , and CH₄ . Yet, with CO₂ at 195 K, it abruptly opens and turns into a rigid porous form that is irreversible via desorption. Once opened by CO₂ , CPM-107 remains in the stable porous state accessible to additional gas types over multiple cycles or CO₂ itself at different temperatures. The porous phase can be re-locked to return to the initial closed phase via re-solvation and desolvation. Such peculiar properties of CPM-107 are apparently linked to a convergence of factors related to both framework and extra-framework features. The unusual CO₂ effect is currently the only available path to porous CPM-107 which shows efficient C₂ H₂ /CO₂ separation.