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 oftenform stable inclusion compounds with a variety of guest species over a wide range of temperature andpressure conditions. In this study, we investigated the pressure-dependent behavior of hydroquinone(HQ) clathrate compounds using a diamond anvil cell. The guest-free and N_2-loaded HQ clathrates weresynthesized by the gas-phase reaction, followed by a controlled heating process to remove CO_2 guestmolecules. The pressure-driven structural transformation of HQ clathrate compounds was observed by acombination of synchrotron X-ray powder diffraction and Raman spectroscopy up to 10 Gpa. TheN_2-loaded HQ clathrate was transformed into a new high-pressure phase at ～ 4.5 Gpa. Upon returningpressure, the new structural phase was reversibly recovered to the original b-form HQ clathrate atambient condition. In contrast, the guest-free HQ clathrate transformed into the a-form HQ at ～ 0.5 Gpaand remained the a-form HQ upon decreasing pressure to ambient condition. This indicates that thepressure-induced structural transition of the guest-free HQ clathrate is completely irreversible. Thisresult provides a useful knowledge on the effect of guest molecules on the stability of structural integrityof organic clathrate compounds.