THE THERMAL DEHYDRATION OF CS(3)LNCL(6)CENTER-DOT-3H(2)O TO CS(3)LNCL(6) (LN=LA-ND) AND THEIR CRYSTAL-STRUCTURES

The crystal structure of Cs3LaCl6 . 3H(2)O has been determined by X ray single crystal analysis. The compound crystallizes from aqueous solution by evaporation at 50 degrees C in the orthorhombic space group Pnma (a = 2124.2(7) pm, b = 865.8(2) pm, and c = 852.3(2) pm, Z = 4). The coordination polyhedra of lanthanum are slightly distorted trigonal prisms triply capped by water molecules. The prisms are connected by common edges forming bent chains [LaCl2Cl4/2(H2O)3](-)(infinity). The three different coordination polyhedra around cesium are associated in three dimensions. The compounds with Ln = Ce, pr, and Nd are isotypic. Upon heating these compounds to 130 degrees C they decompose in one step to Cs(3)LnCl(6) . Cs3LaCl6 and Cs3CeCl6 crystallize into the Cs3BiCl6 type. Cs3PrCl6 and Cs3NdCl6 belong to another type; its structure was determined from X ray single-crystal data of Cs3NdCl6 (space group Pbcm, a = 828.2(2) pm, b = 1322.5(4) pm, c = 2673.0(10) pm, Z = 8). The NdCl6 octahedra are slightly distorted, and the cesium cations are coordinated with 11 or 8 chlorine atoms. Using the notation of ''layers of close-packed octahedra'' the stacking frequency is compared with those of the Cs3BiCl6, K3MoCl6, and Rb3BiBr6 types. When annealing the compounds for several days at 280 degrees C they transform irreversibly into the Cs3BiCl6 structure. (C) 1995 Academic Press, Inc.