Elucidating the guest disorder in structure II argon hydrate – A neutron diffraction isotopic substitution study
Elucidating the guest disorder in structure II argon hydrate – A neutron diffraction isotopic substitution study
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阐明结构 II 水合氩中的客体无序——中子衍射同位素替代研究
DOI：
10.1016/j.jssc.2020.121220
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发表时间：
2020
影响因子：
3.3
通讯作者：
U. Häussermann
中科院分区：
文献类型：
--
作者：
Paulo H. B. Brant Carvalho;Amber Mace;O. Andersson;C. Tulk;J. Molaison;U. Häussermann
具有立方结构II(CS-II)的笼状水合物通常带有大的客体分子，如四氢呋喃、三甲胺氧化物或丙烷。然而，尽管客体的范德瓦尔斯直径相对较小(约3.8亿ä)，但对于水合物Ar也实现了CS-II。本文用中子衍射法研究了在20-95K温度范围内，在常压下，天然Ar和36Ar的结构，其中36Ar的散射率是天然Ar的13倍。该程序允许明确地确定CS-II大笼子内的位置无序，同时精炼宿主和客体结构。分子动力学(MD)模拟表明，即使在20K时，Ar原子的位置无序结构也是由Ar原子的移动引起的。分子动力学势能分布证实了衍射模型。值得注意的是，在所研究的温度范围内，Ar水合物的晶胞体积实际上与N2水合物相同，后者在常压下具有类似的组成，表明主客体相互作用非常相似(略有吸引力)。
Clathrate hydrates with the cubic structure II (CS-II) form typically with large guest molecules, such as tetrahydrofuran, trimethylamine oxide, or propane. However, CS-II is also realized for argon hydrate despite the comparatively small van der Waals diameter of the guest (around 3.8 Å). Here, the structure of deuterated argon hydrate was studied at ambient pressure in the temperature range 20–95 K using neutron diffraction and comparing natural Ar with36Ar, which scatters neutrons more than 13 times more efficiently. The procedure allowed to unambiguously establish the positional disorder within the large cages of CS-II, while simultaneously refining host and guest structures. These cages are singly occupied and off-centered argon atoms distribute on two tetrahedron-shaped split positions with a ratio 3:1. Molecular dynamics (MD) simulations revealed that the crystallographic positional disorder structure is due to mobile argon atoms even at 20 K. The MD potential energy distribution confirmed the diffraction model. It is noted that the unit cell volumes of argon hydrate in the investigated temperature range are virtually identical to N2hydrate, which has a similar composition at ambient pressure, indicating a very similar (slightly attractive) host-guest interaction.
影响因子：
3.3
作者：
Hester, K. C.;Huo, Z.;Sloan, E. D.
通讯作者：
Sloan, E. D.