Transformation of the Hexagonal-Structure Clathrate Hydrate of Cyclooctane to a Low-Symmetry Form Below 167 K

摘要

Clathrate hydrates are crystalline host-guest materials in which small guest molecules are trapped in cages formed by hydrogen-bonded molecules. The three common families of hydrate structures are cubic I (sI), cubic II (sII), and the hexagonal structure H (sH). These crystallographic structures are formed as the different cage types are packed into ordered three-dimensional structures. All three hydrate structures have been identified as naturally occurring, with guest molecules such as hydrocarbon (C1-C8), H2S, CO2, O2, N2, and traces of the noble gases. These clathrate hydrates are found either offshore on the continental margins, under the permafrost, or deep inside glaciers.