Crystal chemistry of the salts Me + Cl · Me 2+ Cl 2 · 2 H 2 O

The crystal chemistry of the double salts Me + Cl · Me 2+ Cl 2 · 2 H 2 O (where (Me + = K, Rb, Cs; Me 2+ = 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 [Me 2+ (H 2 O) 2 Cl 4 ] octahedra form chains having common Cl − corners. Salts with the smaller K + ions crystallize in a tricline system, the [Me 2+ (H 2 O) 2 Cl 4 ] 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 · NiCl 2 · 2 H 2 O–CsCl · MnCl 2 · 2H 2 O–H 2 O system. A continuous series of mixed crystals is found.