SYNTHESIS AND CRYSTAL-STRUCTURE OF KCUGD2S4 - A THREEDIMENSIONAL FRAMEWORK WITH ISOLATED CHANNELS

The reaction of K2S5, Cu, Gd, and S in a 2:1:2:4 molar ratio at 450 de grees C yields yellow-orange needle-like cuboids of the new quaternary compound KCuGd2S4. The crystal structure represents a novel three-dim ensional structure type of quaternary rare earth chalcogenides with al kali metal. The compound crystallizes in the orthorhombic space group Cmcm (No. 63) with a = 3.9921(1) Angstrom, b = 13.523(3) Angstrom, c=1 3.802(3) Angstrom, V=745.1(3) Angstrom(3), Z=4. In the structure GdS6 octahedra and CuS4 tetrahedra are joined by common edges and corners f orming corrugated layers parallel to (010). The GdS6 octahedra are con nected via common edges in the third dimension thus leading to the for mation of a three-dimensional tunnel structure. The potassium cations are confined within the pentagonal shaped channels and are surrounded by eight sulfide anions each.