Structure and Density Comparison of Noble Gas Hydrates Encapsulating Xenon, Krypton and Argon

Abstract

Understanding the effect of guest species on the host framework is important for the development of structure‐based properties of inclusion compounds. Herein, the crystal structures of the noble gas hydrates encapsulating Xe, Kr, and Ar were studied by powder X‐ray diffraction measurements. The crystal structures and hydration numbers of these noble gas hydrates were solved by Rietveld refinements using optimized models with the direct‐space technique. It was revealed that host cage size of these hydrates changed depending on the type of guest species even though their unit‐cell parameters were the same. Based on the structure models obtained, the densities of Xe, Kr, and Ar gas hydrates were also determined to be 1.837, 1.445 and 1.097 g/cm3 at 93 K, respectively. Our findings, from a crystallographic point of view, may give insight into further understanding the thermodynamic stability and physical properties of gas hydrates encapsulating small guests.

Distortion of the Host Water Cages of Structure I Gas Hydrates: Structural Analysis of C2H4 Hydrate by Powder X-ray Diffraction

“…Based on the obtained crystallographic structure of sI C 2 H 4 hydrate at 93 K, the volumes of its 5 12 and 5 12 6 2 cages at 93 K are 165 and 232 Å 3 , respectively, while the volumes of the 5 12 and 5 12 Earlier studies have shown that the 5 12 cages of Xe hydrate (174 Å 3 ) are larger than those of CH 4 hydrate (164 Å 3 ), while the 5 12 6 2 cages of Xe hydrate (226 Å 3 ) are smaller than those of CH 4 hydrate (230 Å 3 ). 32,33 The 5 12 cage of C 2 H 4 hydrate is smaller than that of Xe hydrate, although C 2 H 4 is larger than Xe and the unit cell of C 2 H 4 hydrate is larger than that of Xe hydrate (see Figure 1). Considering these facts, we conclude that the occupancy of the 5 12 cages of C 2 H 4 hydrate, which exceeds that of the 5 12 cages of C 2 H 6 hydrate, accounts for its greater size.…”

Phase Equilibrium of Methane Hydrate Encapsulated Isotopologue 13CH4 and Singly Deuterated Methane

“…The PXRD measurements were performed using an X-ray diffractometer (40 kV, 40 mA; Rigaku model Ultima-III) with parallel-beam optics and a low-temperature chamber. Finely powdered hydrate samples were prepared at a temperature below 100 K using a mortar and were mounted on a PXRD sample holder made of 2.5 mm thick copper (Cu) in the same approach used in our existing study . Each measurement was performed in a θ/2θ step scan mode with a step width of 0.02° using Cu Kα radiation (λ = 1.541 Å).…”

“…Finely powdered hydrate samples were prepared at a temperature below 100 K using a mortar and were mounted on a PXRD sample holder made of 2.5 mm thick copper (Cu) in the same approach used in our existing study. 18 Each measurement was performed in a θ/2θ step scan mode with a step width of 0.02°u sing Cu Kα radiation (λ = 1.541 Å).…”

Assessment of DFT approaches in noble gas clathrate-like clusters: stability and thermodynamics

“…Noble gas hydrates, and specifically helium clathrates, are perhaps one of the systems with less information available. [24][25][26][27][28][29][30][31][32][33][34][35] Although helium atoms and water molecules are the most frequent mono-and triatomic entities, respectively, in the universe, their interactions are weak and therefore, compounds are difficult to form. Nevertheless, it was possible to obtain the first helium clathrate hydrate in 2018 by filling ice XVI with helium atoms.…”