Locating gases in porous materials: cryogenic loading of fuel-related gases into a Sc-based metal-organic framework under extreme pressures

An alternative approach to loading metal organic frameworks with gas molecules at high (kbar) pressures is reported. The technique, which uses liquefied gases as pressure transmitting media within a diamond anvil cell along with a single-crystal of a porous metal-organic framework, is demonstrated to have considerable advantages over other gas-loading methods when investigating host-guest interactions. Specifically, loading the metal-organic framework ScBDC with liquefied CO at 2 kbar reveals the presence of three adsorption sites, one previously unreported, and resolves previous inconsistencies between structural data and adsorption isotherms. A further study with supercritical CH at 3-25 kbar demonstrates hyperfilling of the ScBDC and two high-pressure displacive and reversible phase transitions are induced as the filled MOF adapts to reduce the volume of the system. The maximum gas uptake of porous MOFs was explored by using gases as pressure-transmitting media in high-pressure single-crystal diffraction experiments. A study with supercritical CH at 3-25 kbar demonstrates that two high-pressure phase transitions are induced as the filled MOF adapts to reduce the volume of the system.