Abstract. Crystals of ordered and disordered Ba 7 F 12 Cl 2 were prepared by flux growth and solid state reactions. These new structures were characterized by single crystal and powder X-ray diffraction. The disordered variant which shows disorder on one of the cation sites was obtained from a BaF 2 + BaCl 2 + NaCl/NaF flux. It has hexagonal space group P6 3 /m (176) with one formula unit per unit cell. The lattice constants are a = b = 1059.55(5) pm and c = 420.10(4) pm (at 21°C). The structure was refined to R(R w ) = 0.026(0.030) for 346 independent reflections and 26 parameters. Slow cooling of a mixture of BaF 2 and LiCl yields the ordered variant. This one crystallizes in the hexagonal space group P6 (174) with one formula per unit cell. Lattice constants at 21°C are a = b = 1063.46(2) pm and c = 417.52(1) pm. The structure was refined to R(R w ) = 0.017 (0.017) for 638 independent reflections and 45 parameters. The structural arrangement and the interatomic distances of the two variants are mutually similar. The barium atoms have coordination number nine. Propeller-type arrangements with a chloride ion on the axis and the fluoride ions as blades are observed. These latter ones are interconnected into`channels' of tricapped fluoride prisms. Occupation disorder of the barium sites in the channels of the disordered variant makes the main difference between the two. An unexpectedly high X-ray density obtained for both variants of Ba 7 F 12 Cl 2 can be correlated to the density of other barium fluorohalides having a coordination number of nine for the barium ion. Der strukturelle Aufbau und die atomaren Absta È nde beider Varianten sind anna È hernd gleich. Die Bariumatome haben die Koordinationszahl neun. Es werden propellerartige Anordnungen mit einem Chloridion in der Achse und den Fluoridionen als Flu È gel beobachtet. Die letzteren sind durch Kana È le von dreifach bekappten Fluoridprismen verbunden. Die Besetzung der fehlgeordneten Bariumlagen in den Kana È len der Fehlordnungsvariante ist der wesentliche Unterschied zwischen beiden Varianten. Die unerwartet hohe Ro È ntgendichte fu È r beide Formen von Ba 7 F 12 Cl 2 entspricht der Dichte anderer Bariumfluoridhalogenide mit der Koordinationszahl 9 fu È r das Bariumatom
