Crystal structures of hydrates of simple inorganic salts. I. Water-rich magnesium halide hydrates MgCl2•8H2O, MgCl2•12H2O, MgBr2•6H2O, MgBr2•9H2O, MgI2•8H2O and MgI2•9H2O

The previously reported structures of the hydrates of simple inorganic salts that crystallize at room temperature are generally well determined. This is not true for water-rich hydrates, which crystallize at temperatures below 273 K. In this series, investigations of the crystal structures of water-rich hydrates crystallized from aqueous solutions at low temperatures are presented. Reported herein are the structures of a set of magnesium salts. Crystals of MgCl28 center dot H2O (magnesium dichloride octahydrate), MgCl2 center dot 12H(2)O (magnesium dichloride dodecahydrate), MgBr2 center dot 6H(2)O (magnesium dibromide hexahydrate), MgBr2 center dot 9H(2)O (magnesium dibromide nonahydrate), MgI2 center dot 8H(2)O (magnesium diiodide octahydrate) and MgI2 center dot 9H(2)O (magnesium diiodide nonahydrate) were grown from their aqueous solutions at temperatures below 298 K according to the solid-liquid phase diagrams. All structures are built up from Mg(H2O)(6) octahedra. Dimensions and angles in the hexaaqua cation complexes are very similar and variation is not systematic. The anions are incorporated into a specific network of O-H center dot center dot center dot X hydrogen bonds.