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 CO 2 . CPM‐107 contains Mg 2 ‐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 N 2 , H 2 , and CH 4 . Yet, with CO 2 at 195 K, it abruptly opens and turns into a rigid porous form that is irreversible via desorption. Once opened by CO 2 , CPM‐107 remains in the stable porous state accessible to additional gas types over multiple cycles or CO 2 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 CO 2 effect is currently the only available path to porous CPM‐107 which shows efficient C 2 H 2 /CO 2 separation.