Structure, Preparation, and General Properties
MgCl2 crystallizes in the cadmium chloride motif, which features octahedral Mg. A variety of hydrates are known with the formula MgCl2(H2O)x, and each loses water with increasing temperature: x = 12 (-16.4 °C), 8 (-3.4 °C), 6 (116.7 °C), 4 (181 °C), 2 (ca. 300 °C). In the hexahydrate, the Mg2+ remains octahedral, but is coordinated to six water ligands. The thermal dehydration of the hydrates MgCl2(H2O)x (x = 6, 12) does not occur straightforwardly.
As suggested by the existence of some hydrates, anhydrous MgCl2 is a Lewis acid, although a very weak one.
In the Dow process, magnesium chloride is regenerated from magnesium hydroxide using hydrochloric acid:
- Mg(OH)2(s) + 2 HCl → MgCl2(aq) + 2 H2O(l)
It can also be prepared from magnesium carbonate by a similar reaction.
In most of its derivatives, MgCl2 forms octahedral complexes. Derivatives with tetrahedral Mg2+ are less common. Examples include salts of (tetraethylammonium)2MgCl4 and adducts such as MgCl(TMEDA).
Read more about this topic: Magnesium Chloride
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