Ternäre Halogenide vom Typ A3MX6. III [1, 2]. Synthese,Strukturen und Ionenleitfähigkeit der Halogenide Na3MX6 (X = Cl,Br)

Ternary Halides of the A₃MX₆ Type. III 1, 2]. Synthesis, Structures, and Ionic Conductivity of the Halides Na₃MX₆ (X = Cl, Br) The bromides Na₃MBr₆ crystallize with the stuffed LiSbF₆-type structure (type I; M = Sm? Gd) or with the structure of the mineral cryolite (type II; M = Gd? Lu). The structure types were refined from single crystal X-ray data (Na₃SmBr₆: trigonal, space group R3 , a = 740.8(2) pm, c = 1 998.9(8) pm, Z = 3; Na₃YBr₆: monoclinic, space group P2₁/n, a = 721.3(4) pm, b = 769.9(2) pm, c = 1 074.8(4) pm, β = 90.60(4)°, Z = 2). Reversible phase transitions from one structure to the other occur. The phase transition temperatures were determined for the bromides as well as for the chlorides Na₃MCl₆ (M = Eu? Lu). The refinement of both structures for one compound was possible for Na₃GdBr₆ (I: trigonal, space group R3 , a = 737.1(5) pm, c = 1 887(2) pm, Z = 3; II: monoclinic, space group P2₁/n, a = 725.2(1) pm, b = 774.1(3) pm, c = 1 080.1(3) pm, β = 90.76(3)°, Z = 2). All compounds exhibit ionic conductivity of the sodium ions which decreases with the change from type I to type II. The conductivity of the bromides is always higher when compared with the respective chlorides.