In Situ Monitoring of Unique Switching Transitions in the Pressure-Amplifying Flexible Framework Material DUT-49 by High-Pressure 129Xe NMR Spectroscopy

Abstract

The pronounced flexibility of special metal–organic frameworks (MOFs), so-called soft porous crystals, is attracting increasing research interest. Studies of host–guest interactions in such materials are especially powerful if the measurements are performed in situ. 129Xe NMR spectroscopy is favorable because it provides characteristic, structure-sensitive parameters such as chemical shifts. The combination of high-pressure xenon adsorption with 129Xe NMR spectroscopy was used to elucidate the adsorption-induced phase transitions in the recently discovered pressure-amplifying framework material DUT-49, showing a unique negative gas adsorption (NGA) transition. In the open-pore state, DUT-49op exhibits a hierarchical pore system involving both micro- and mesopores. After reaching a critical relative pressure of ca. 0.15, adsorbed xenon induces mesopore contraction, resulting in a purely microporous contracted-pore phase. This contraction is accompanied by release of xenon from the mesopores. Further increa...