CRYSTAL-CHEMISTRY OF THE SALTS ME(-CENTER-DOT-ME(2+)CL(2)CENTER-DOT-2H2O()CL)

The crystal chemistry of the double salts Me(+)Cl . Me(2+)Cl(2) . 2H(2 )O (where Me(+) = K, Rb, Cs; Me(2+) = Mn, Fe, Co, Ni) is considered. I t is concluded that these salts crystallize in three types of structur es, the Me+ ion size being decisive for the structure type. Salts cont aining the large Cs+ ions crystallize in an orthorhombic structure in which [Me(2+)(H2O)(2)Cl-4] octahedra form chains having common Cl- cor ners. Salts with the smaller K+ ions crystallize in a tricline system, the [Me(2+)(H2O)(2)Cl-4] octahedra being connected by a common Cl-Cl edge and forming dimers. When the intermediate in size Rb+ ions are pr esent in the salts, either of the above structures is possible as well as a monoclinic structure which is intermediate in symmetry. The expe cted isostructure of the cesium salts was checked by studing the CsCl . NiCl2 . 2H(2)O - CsCl . MnCl2 . 2H(2)O - H2O system. A continuous se ries of mixed crystals is found.