Ce 29 Al 14 I 28 : Ein Komposit aus intermetallischer Phase und Metallclustern

Ce 29 Al 14 I 28 : A Composite of Intermetallic Phase and Metal Clusters Single crystals of Ce 29 Al 14 I 28 form at 900 °C from CeI 3 , Ce and Al. The compound crystallises in C 2/ m with a = 19.471(3), b = 4.308(1), c = 19.526(3) Å und β = 102.75(2)°. Pronounced diffuse scattering occurs and is discussed in terms of special disordered arrangements of discrete building units. The structure of Ce 29 Al 14 I 28 is composed of two characteristic substructures. One part of the Ce atoms forms pairs of face‐linked trigonal prisms which are connected into layers via edges. Al atoms in the prism centers are arranged in ribbons of planar Al 6 rings as in the structure of Ce 3 Al 2 I 2 . Between these ordered layers another kind of layers of close‐packed I atoms occur whose octahedral voids are partially occupied by Ce atoms. Some of the I‐atoms are substituted by Al which are completely surrounded by Ce atoms resulting in octahedral Ce 6 Al clusters. Most of these clusters are connected into Ce 10 Al 2 units via edge‐sharing, and such units are rather ordered within one layer, however, with no long range order and no correlation with adjacent layers. The prism layers represent sections of an intermetallic phase which are separated by non‐metallic cluster structures.