Coupling external and internal pressure for the structural transition of MIL-53(Cr)†
Flexible metal–organic framework (MOF) materials have the ability to perform stimulated sudden volume contractions, and thus attract increasing attention for use in potential applications such as: actuators or sensors. Here, the structural transition of MIL-53(Cr) loaded with a high concentration of CH3OH (CH3OH) guest molecules, which cause internal pressure due to guest–guest interactions, was investigated. The pressure triggering the structural transition can be enhanced by high guest molecule loadings (1 CH3OH per unit cell (UC): 5 MPa, empty: 53 MPa, 7 CH3OH per UC: 90 MPa, and 8 CH3OH per UC: 280 MPa). The asymmetrical and small distortion of the organic–inorganic connections are the main microscopic characteristic of the structural transition of MIL-53(Cr) with a high CH3OH loading. The external pressure and the internal pressure, instead of the adsorption of the guest molecules, became dominant in the structural transition of MIL-53(Cr). Current studies showed that the high-pressure response of the flexible MOF structure may broaden the acceptable pressure range in future actuator or sensor applications.