Crystal structures of hydrates of simple inorganic salts. I. Water-rich magnesium halide hydrates MgCl 2 ·8H 2 O, MgCl 2 ·12H 2 O, MgBr 2 ·6H 2 O, MgBr 2 ·9H 2 O, MgI 2 ·8H 2 O and MgI 2 ·9H 2 O

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 MgCl 2 ·8H 2 O (magnesium dichloride octahydrate), MgCl 2 ·12H 2 O (magnesium dichloride dodecahydrate), MgBr 2 ·6H 2 O (magnesium dibromide hexahydrate), MgBr 2 ·9H 2 O (magnesium dibromide nonahydrate), MgI 2 ·8H 2 O (magnesium diiodide octahydrate) and MgI 2 ·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(H 2 O) 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... X hydrogen bonds.