Pressure-Induced Reversible and Irreversible Structural Transitions of a Hydrogen-Bonded Organic Framework

摘要

Organic clathrate can be used as the potential host materials for gas storage, because they often form stable inclusion compounds with a variety of guest species over a wide range of temperature and pressure conditions. In this study, we investigated the pressure-dependent behavior of hydroquinone (HQ) clathrate compounds using a diamond anvil cell. The guest-free and N2-loaded HQ clathrates were synthesized by the gas-phase reaction, followed by a controlled heating process to remove CO2 guest molecules. The pressure-driven structural transformation of HQ clathrate compounds was observed by a combination of synchrotron X-ray powder diffraction and Raman spectroscopy up to 10 GPa. The N2-loaded HQ clathrate was transformed into a new high-pressure phase at ～ 4.5 GPa. Upon returning pressure, the new structural phase was reversibly recovered to the original b-form HQ clathrate at ambient condition. In contrast, the guest-free HQ clathrate transformed into the a-form HQ at ～ 0.5 GPa and remained the a-form HQ upon decreasing pressure to ambient condition. This indicates that the pressure-induced structural transition of the guest-free HQ clathrate is completely irreversible. This result provides a useful knowledge on the effect of guest molecules on the stability of structural integrity of organic clathrate compounds.