AB 2 X 2-Verbindungen im CaAl2Si2-Typ, VI Zur Struktur von ThCu2P2, YbZn2P2 und YbZnCuP2 sowie der verwandten Verbindungen YbCu3P2 und YbCu2P2

Abstract

Abstract X-Ray investigations on the trigonal crystallizing compounds YbZn2P2 (a = 4.035 Å, c = 6.774Å), YbZnCuP2 (a = 3.946 Å, c = 6.462 Å) and ThCu2P2 (a = 4.028 Å, c = 6.469 Å) revealed a CaAl2Si2-type structure. In order to establish the limits of existence of the CaAl2Si2-type, the new compounds YbCu2P2 and YbCu3P2 have been prepared and structurally solved. YbCu3P2 crystallizes in a trigonal-rhombohedral structure (hexagonal axes: a = 3.964Å, c = 40,296Å, c/a = 10.165, S.G. R[unk]m, Z = 6, all atoms in 6c) with a structure in which Yb-atoms are surrounded by 6 P-atoms in form of a distorted octahedron. They embrace two kinds of blocks, as they are observed in the CaAl2Si2-structure (CuP-blocks) and recognized in Cu3P (Cu2P-blocks). CuP- and Cu2P-blocks show a regular alternating sequenze. YbCu2P2, for which the structural determination showed the approximate stoichiometry YbCu≈2.2P2, was obtained besides YbP and crystallizes also in a trigonal-rhombohedral structure (hexagonal axes: a = 3.951 Å, c = 59.46 Å, c/a = 15.05, S.G. R[unk]m, Z = 9, Yb(l) in 3a, all other atoms in 6c, three of four Cu-positions partially occupied). The Yb-atoms are also surrounded by P-atoms in a distorted octahedron and include, as in the copper-rich compound, CuP- and Cu2P-blocks. However there are twice as many CuP-blocks as Cu2P-blocks. As the atomic distances show, Ytterbium is probably trivalent in both compounds.