The hydrocarbon-bearing clathrasil chibaite and its host-guest structure at low temperature
- Author(s)
- Katharina Sarah Scheidl, Herta Silvia Effenberger, Takehiko Yagi, Koichi Momma, Ronald Miletich
- Abstract
The natural sII-type clathrasil chibaite [chemical formula SiO2·(M12,M16), where Mx denotes a guest molecule] was investigated using single-crystal X-ray diffraction and Raman spectroscopy in the temperature range from 273 to 83 K. The O atoms of the structure at room temperature, which globally conforms to space group [Fd{\overline 3}m] [V = 7348.9 (17) Å3, a = 19.4420 (15) Å], have anomalous anisotropic displacement parameters indicating a static or dynamic disorder. With decreasing temperature, the crystal structure shows a continuous symmetry-lowering transformation accompanied by twinning. The intensities of weak superstructure reflections increase as temperature decreases. A monoclinic twinned superstructure was derived at 100 K [A2/n, V = 7251.0 (17) Å3, a′ = 23.7054 (2), b′ = 13.6861 (11), c′ = 23.7051 (2) Å, β′ = 109.47°]. The transformation matrix from the cubic to the monoclinic system is ai′ = (½ 1 ½ / ½ 0 −½ / ½ −1 ½). The A2/n host framework has Si-O bond lengths and Si-O-Si angles that are much closer to known values for stable silicate-framework structures compared with the averaged [Fd{\overline 3}m] model. As suggested from band splitting observed in the Raman spectra, the [512]-type cages (one crystallographically unique in [Fd{\overline 3}m], four different in A2/n) entrap the hydrocarbon species (CH4, C2H6, C3H8, i-C4H10). The [51264]-type cage was found to be unique in both structure types. It contains the larger hydrocarbon molecules C2H6, C3H8 and i-C4H10.
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- University of Tokyo, National Museum of Nature and Science
- Journal
- IU Cr J
- Volume
- 5
- Pages
- 595-607
- No. of pages
- 13
- ISSN
- 2052-2525
- DOI
- https://doi.org/10.1107/S2052252518009107
- Publication date
- 08-2018
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 104026 Spectroscopy, 104011 Materials chemistry, 105113 Crystallography
- Keywords
- ASJC Scopus subject areas
- Condensed Matter Physics, General Chemistry, General Materials Science, Biochemistry
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/4c1e2c3f-bdd7-48d5-8502-1aa399b105d3