Structural Transformation and Guest Dynamics of Methanol-Loaded Hydroquinone Clathrate Observed by Temperature-Dependent Raman Spectroscopy

Abstract

The structural transformations and guest dynamics of methanol-loaded β-form hydroquinone (HQ) clathrate were investigated using temperature-dependent Raman spectroscopy. Methanol-loaded β-form HQ clathrate was obtained by recrystallization and characterized by elemental analysis, synchrotron X-ray diffraction, solid-state (13)C NMR spectroscopy, and Raman spectroscopy. Temperature-dependent Raman spectra of methanol-loaded β-form HQ clathrate were measured in the temperature range 300-412 K at increments of 4 K. Although no significant changes were evident in the temperature range 300-376 K, abrupt changes in the relative intensity and shape of the Raman bands were observed between 380 and 412 K indicating the structural transition from methanol-loaded β-form HQ clathrate to pure α-form HQ. Methanol molecules were gradually released from the β-form HQ clathrate in the range 364-380 K. Upon returning to ambient conditions, the crystal structure of the HQ sample remained identical to that of pure α-form HQ. Therefore, the temperature-induced structural transition of methanol-loaded HQ clathrate is completely irreversible and α-form HQ is more stable at ambient conditions.

Extremely Slow Diffusion of Argon Atoms in Clathrate Cages: Implications for Gas Storage in Solid Materials

“…It should be noted that this temperature is very close to the dissociation temperature of HQ clathrates including other guests such as CH 4 , CO 2 , and methanol. 11,18,29 Since there is no penetration pathway along directions perpendicular to the c-axis, the diffusion path of argon atoms is essentially along the c-axis in the direction parallel to the long axis of the cage, 30 leading to a reasonable approximation of 1D diffusion. The argon atoms migrate via the 1D cage nanochannels connected by the hydrogen-bonded hexagon between the ∼4 Å-sized cages composed of host HQ molecules (Figure 3d).…”

Enhanced Hydrogen-Storage Capacity and Structural Stability of an Organic Clathrate Structure with Fullerene (C60) Guests and Lithium Doping

“…42,43 The chemical shift of carbon atoms attached to the hydroxyl groups of host HQ molecules appears S3). 30,33,44 Fullerene (C 60 ), a very stable solid, has a high-symmetry truncated icosahedral structure with a round hollow cage. 45,46 Although the face-centered cubic (fcc) phase of bulk C 60 (fullerite) shows an isothermal bulk modulus of K = 18.1 GPa and K′(dK/dP) = 5.7, the compressibility of the C 60 molecule is significantly lower than that of the bulk fullerite solid.…”

“…30,31 However, HQ clathrates are unsuitable for practical applications at high temperatures because of their poor thermal stability, which stems from their structural transformation and inherent sublimation characteristic. 28,32,33 Another important drawback pertaining to the structural stability of the HQ clathrates is that they undergo structural transformations under high pressures and exhibit a gradual release of guest molecules from the HOF framework. 34−36 Here we report that the C 60 -loaded HQ (C 60 −HQ) clathrate reveals enhanced structural stability because of the presence of large guest C 60 molecules templating the cages.…”

“…HOFs can potentially adopt one-dimensional (1D) channel structures along the hexagonal c -axis, as defined by the hexagonal entrance of hydrogen-bonded host HQ molecules. The flexible hexagon allows the migration of guest molecules into the HOFs via a dynamic pore-widening process, leading to the controlled and reversible storage of small molecules. , However, HQ clathrates are unsuitable for practical applications at high temperatures because of their poor thermal stability, which stems from their structural transformation and inherent sublimation characteristic. ,, Another important drawback pertaining to the structural stability of the HQ clathrates is that they undergo structural transformations under high pressures and exhibit a gradual release of guest molecules from the HOF framework. − …”

Thermal Properties and Transition Behavior of Host-Guest Compounds Under High Pressure

“…Hydroquinone ( , with methanol guests [38], and commonly roughly similar values for a and c for the β-form with other guest species, e.g. HCl, HBr, H 2 S, C 2 H 2 and SO 2 [39,40].…”