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 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 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.