What are clathrate compounds

content1 Introduction 2. hydrogen3. Noble gases4. Halogens5. Chalcogens6. Pentele7. Tetrele8. Boron

Long before the first real noble gas compounds could be represented for the first time, the clathrates or cage compounds or ice hydrates were considered the only 'compounds' of the noble gases. However, these are so-called inclusion compounds, in which the elementary noble gases are enclosed in the cages of water molecules. That of the clathrates of type I is 8 X * 46 H2O (X = noble gas or halogen). These compounds can be created simply by freezing out water in the presence of noble gases or halogens (e.g. elemental chlorine). The noble gas hydrates consist of an H like normal ice2O framework in which every O atom is tetrahedrally coordinated. In contrast to simple ice, when the noble gases are present, which act as templates, structures with large cavities are formed. In the Clathrat-I it concerns

  • Two pentagonal dodecahedra (), which consist of 12 pentagons and 20 corners (Platonic solid). These pentagon dodecahedra form the smaller gaps with a diameter of approx. 520 pm.
  • Six so-called fourteen faces (), which have 2 hexagons and 12 pentagons as boundary surfaces and a total of 24 corners. These polyhedra represent the large gaps, their diameter is 590 pm.
These two polyhedra are room dividers, they parquet the room completely (fill the room without gaps).
Fig. 3.2.1. Structures of the clathrate hydrates

According to the template effect of the guests, the occupation of these cavities depends on the enclosed compounds:

  • If X are simple noble gases, then all eight gaps are filled so that the general formula (6 + 2) X * 46 H2O results.
  • If, on the other hand, X is a large molecule, then only the 14 faces are occupied and the formula 6 CHCl results3 * 46 H.2O.
The gas hydrates find their way into exactly matching cavities for absorption, e.g. also for the separation of differently shaped hydrocarbons.

The structural chemistry of the clathrasils is described in detail in Chap. 8.7 of the lecture silicate chemistry. There are also intermetallic phases with the Tetrel elements and alkali metals in the gaps, which have the same structure, see e.g. Chap. 6.2. of the intermetallic phases.

content1 Introduction 2. hydrogen3. Noble gases4. Halogens5. Chalcogens6. Pentele7. Tetrele8. Boron