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 °C yields yellow-orange needle-like cuboids of the new quaternary compound KCuGd₂S₄. The crystal structure represents a novel three-dimensional structure type of quaternary rare earth chalcogenides with alkali metal. The compound crystallizes in the orthorhombic space group Cmcm (No. 63) with a = 3.9921(1) Å, b = 13.523(3) Å, c = 13.802(3) Å, V = 745.1(3) ų, Z = 4. In the structure GdS₆ octahedra and CuS₄ tetrahedra are joined by common edges and corners forming corrugated layers parallel to (010). The GdS₆ octahedra are connected via common edges in the third dimension thus leading to the formation of a three-dimensional tunnel structure. The potassium cations are confined within the pentagonal shaped channels and are surrounded by eight sulfide anions each.