Chem1 General Chemistry Virtual Textbook → Ste → Introduction

Porous Solids

Clathrates, clays, and surfaces

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5 Clathrates and inclusion compounds

There are a number of molecules and ionic compounds whose crystal structures are sufficiently open to permit the inclusion of some other molecule within their cage-like structure. These compounds are known as clathrates. The guest molecules are generally non-polar and small, which means that they are normally gases in their pure forms under normal conditions.

The structure of ice is especially open, and it is not surprising that it should form clathrate type hydrates with a variety of molecules, including xenon, dichlorine (Cl2 · 8H2O was discovered by Humphrey Davy in 1811), xenon (Xe4 · 23H2O), and methane ((CH4)4 ·23H2O)

#### Methane hydrates

These are of special interest owing to their widespread natural occurance in oceanic sediments and their connection to the global carbon cycle, global warming and tsunamis. See this Wesleyan University page for an interesting discussion.

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These gas hydrates are stabilized mainly by dipole-induced dipole attraction, and tend to decompose when they are warmed. It has been proposed that compounds such as these could play an important role in the chemistry of many of the colder planets that are composed partly of frozen hydrogen-bonded substances such as water and ammonia.

Clays

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