Activation‐Dependent Breathing in a Flexible Metal–Organic Framework and the Effects of Repeated Sorption/Desorption Cycling

Abstract A non‐interpenetrated metal–organic framework with a paddle‐wheel secondary building unit has been activated by direct thermal evacuation, guest exchange with a volatile solvent, and supercritical CO 2 drying. Conventional thermal activation yields a mixture of crystalline phases and some amorphous content. Exchange with a volatile solvent prior to vacuum activation produces a pure breathing phase with high sorption capacity, selectivity for CO 2 over N 2 and CH 4 , and substantial hysteresis. Supercritical drying can be used to access a guest‐free open phase. Pressure‐resolved differential scanning calorimetry was used to confirm and investigate a systematic loss of sorption capacity by the breathing phase as a function of successive cycles of sorption and desorption. A corresponding loss of sample integrity was not detectable by powder X‐ray diffraction analysis. This may be an important factor to consider in cases where flexible MOFs are earmarked for industrial applications.