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 C2H2/CO2 separation. [ABSTRACT FROM AUTHOR]