Crystal chemistry of the salts Me+Cl · Me2+Cl2 · 2 H2O

The crystal chemistry of the double salts Me⁺Cl · Me²⁺Cl₂ · 2 H₂O (where (Me⁺ = K, Rb, Cs; Me²⁺ = Mn, Fe, Co, Ni) is considered. It is concluded that these salts crystallize in three types of structures, the Me⁺ ion size being decisive for the structure type. Salts containing the large Cs⁺ ions crystallize in an orthorhombic structure in which Me²⁺ (H₂O)₂Cl₄] octahedra form chains having common Cl^? corners. Salts with the smaller K⁺ ions crystallize in a tricline system, the Me²⁺ (H₂O)₂Cl₄] octahedra being connected by a common Cl–Cl edge and forming dimers. When the intermediate in size Rb⁺ ions are present in the salts, either of the above structures is possible as well as a monoclinic structure which is intermediate in symmetry. The expected isostructure of the cesium salts was checked by studing the CsCl · NiCl₂ · 2 H₂O–CsCl · MnCl₂ · 2H₂O–H₂O system. A continuous series of mixed crystals is found.