TERNARY HALIDES OF THE A3MX6 TYPE .1. A3YCL6 (A = K, NH4, RB, CS) - SYNTHESIS, STRUCTURES, THERMAL-BEHAVIOR - SOME ANALOGOUS CHLORIDES OF THE LANTHANIDES

Reaction of the trichlorides MCl3 (M = Y, Tb-Lu) with alkali chlorides ACI (A = K, Rb, Cs) in evacuated silica ampoules at 850-900-degrees-C yields A3MCl6-type chlorides. (NH4)3YCl6 is obtained via the ammonium-chloride route. The crystal structure of Rb3YCl6 (monoclinic, C2/c (no. 15), Z = 8, a = 2 5 83(1) pm, b = 788.9(4) pm, c = 1283.9(7) pm, beta = 99.63(4)-degrees, R = 0.062, R(w) = 0.050) is that of CS3BiCl6. The Rb3YCl6/CS3BiCl6 structure and the closely related structures of K3MoCl6 and In2Cl3 are derived from the elpasolite-type of structure (K2NaAlF6) making use of the model of closest-packed layer structures. Cell parameters for the chlorides Rb3MCl6 (M = Y, Tb-Lu) and Cs3YCl6 and CS3ErCl6 as well, which are all isostructural with Rb3YCl6, are given. The ''system'' (K, NH4, Rb, CS)YCl6 has been investigated by DTA and high-temperature X-ray powder diffractometry.