(181ak) Pressure-Induced Reversible and Irreversible Structural Transitions of Hydroquinone Clathrates

Pressure-Induced
Reversible and Irreversible Structural Transitions of Hydroquinone Clathrates

Byeong-Soo Kim,* Jeong-Woo Park, Sulki An, Youngrok
Seo, Ji-Ho Yoon

Department of
Energy & Resources Engineering, Korea Maritime University, Busan 606-791, Korea

Abstract

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.