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Clathrate: structure of an inclusion compound of urea and 1,6-dichlorohexane. Color scheme: oxygen: red, nitrogen: blue, chlorine: green, carbon: black, hydrogen: white.

Clathrates (from Latin clatratus , `` latticed '' ; spelling in German sometimes also clathrates ) are inclusion compounds of two substances, of which a guest molecule is embedded in a grid or cage made of a host molecule. They are therefore also called cage inclusion connections .

Inclusion compounds of gaseous substances in water are also known as gas hydrates . In the case of clathrates with water, the gas / water molar ratio is usually 8:48, and in the case of large gas particles to be stored it is also 6:48. Methane hydrate arises from natural methane sources at great depths in cold seas. It is stable at temperatures only slightly above 0 ° C.

In large glaciers (e.g. at the South Pole ), air (from the snow that forms the glacier) is gradually built into the ice as a clathrate at a depth of a few 100 meters under the pressure prevailing there.

In addition to water, some organic compounds can also form clathrates, for example hydroquinone forms an inclusion compound with argon in a ratio of 3: 1. More reactive gases such as hydrogen halides or hydrogen sulfide can also be embedded in organic compounds .

A distinction must be made between clathrates and interstitial solid solutions , compounds of metals with non-metals, and complex compounds , which are real chemical compounds.

Technical application

Clathrates are used technically in urea extractive crystallization . This is used for selective separation of n paraffins from iso -Paraffin-, aromatic, naphthenic and n -paraffin mixtures ( kerosene ). The urea forms channels with a diameter of 0.53 nanometers during crystallization. Only n -paraffins can penetrate these small channels and be bound there. At 75 ° C, the urea crystal dissolves again in water and the n -paraffins are released.

Individual evidence

  1. Entry on clathrates . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.C01097 Version: 2.1.5.
  2. ^ Entry on clathrates. In: Römpp Online . Georg Thieme Verlag, accessed on June 9, 2013.