GD4I6CN - A CARBIDE NITRIDE WITH CHAINS O F GD-6(C-2) OCTAHEDRA AND GD6N2 DOUBLE TETRAHEDRA

The compound alpha-Gd4I6CN is prepared by reaction of Gd, GdI3, C, and GdN (1:2:1:1 mole ratio) at 1170 K in sealed Ta tubes. It is obtained as brown red, transparent needles which are air and moisture sensitiv e. The structure of alpha-Gd4I6CN contains Gd-6 octahedra centered by C-2 groups and double tetrahedra centered by N atoms. The units are al ternatingly connected via common edges to form chains (Gd2Gd4/2C2)(Gd2 /2Gd2/2N)(2) parallel [001]. The linear chains are surrounded by I ato ms above all free edges of the metal polyhedra and linked according to (Gd2Gd4/2C2)(Gd2Gd4/2N2)I4/2I8I2 in the a-b plane. We also found beta -Gd4I6CN, which is formed in a monotropic transition from the alpha-fo rm. In the structure the chains of Gd octahedra and tetrahedra as desc ribed for alpha-Gd4I6CN are more densely packed. The structure of Y6I9 C2N is composed by chains of pairs of Y-octahedra and Y-tetrahedra, re spectively. The octahedra are centered by C-2 groups, the tetrahedra b y N-atoms. We also synthesized the compounds Gd4Br6CN und La4I6CN by t empering at 1220 K. They are isotypic with alpha-Gd4I6CN.