Crystal structures of RuSe2, OsSe2, PtAs2, and α-NiAs2

Abstract

The atom positions in RuSe2, OsSe2, PtAs2, and α-NiAs2 have been determined from X-ray powder diffraction data. In the pyrite-type compounds (Pa3), the metal atoms are in 4(a), the face-centered positions, and the nonmetal atoms in 8(c), with x = 0.381 ± 3 (RuSe2, a = 5.935 Å); x = 0.382 ± 4 (OsSe2, a = 5.946 Å); and x = 0.385 ± 4 (PtAs2, a = 5.967 Å).In orthorhombic α-NiAs2 (Pbca, a = 5.770, b = 5.838, c = 11.419 Å), the atom positions are[Formula: see text]As in the marcasite and pyrite structures, the nonmetal atoms in α-NiAs2 are paired, and the metal atoms have six nearest nonmetal neighbors at the corners of a distorted octahedron. Between metal atom layers these octahedra are coordinated alternately by corner sharing only, as in the pyrite lattice, and by a combination of corner and edge sharing, as in the marcasite lattice. The mean Ni—As distance is 2.38 Å, with minimum and maximum distances of 2.25 and 2.46 Å. The As—As distance is 2.46 Å, and the shortest Ni—Ni distance is 3.72 Å.