Magnesium chloride tetra­hydrate, MgCl₂·4H₂O

The structure of the title compound is built up from MgCl₂(H₂O)₄ octa­hedra with a trans configuration. Each complex is situated on a crystallographic twofold axis, with the rotation axis aligned along one H₂O—Mg—OH₂ axis. They are connected by a complex network of O—H...Cl hydrogen bonds. The structure contains two-dimensional sections that are essentially identical to those in the reported tetra­hydrates of CrCl₂, FeCl₂, FeBr₂ and CoBr₂, but they are stacked in a different manner in MgCl₂·4H₂O compared with the transition metal structures.