Geometrical Coordination in Brucite

A picture of the geometric coordination along the (110)-plane in brucite is shown below.

Unit cell of Brucit

The geometrical coordination in Brucite, showing the diagonal mirror plane through the unit cell.

Each hydrogen atom forms a common face with the oxygen of the hydroxy-group and a smaller face with the oxygen of the hydroxy-group in the next layer. In addition several geometric coordinations to hydrogen and magnesium can be seen. As the hydrogen lies on a three-fold axis, the complete coordination geometric coordination is given below:

O 1 0.99
H 3 1.93
O 3 2.46
Mg 3 2.74
H 6 3.14
Mg 3 3.27
H 3 3.69

This gives a total geometric coordination number of 22 which is reduced to a chemical coordination number of 4. For Ca(OH)2 and under pressure slightly different coordinations may be result with the chemical coordination number rising to 5. But the 4 above described hydrogen bonds are stable in all brucite-like structures and over the whole pressure range.

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Last Updated: 26 October 1996