The crystal structure of Sb2Se3 has been redetermined with 610 independent reflections, using three-dimensional intensities measured on a computer-controlled Philips PW 1100 single-crystal diffractometer. The structure does not deviate in principle from that proposed by Dönges (1950) and Tideswell, Kruse, Mc Cullough (1957), but it shows interesting details. The cell constants, obtained by least-squares calculation from direct θ-value measurements on the diffractometer, are: a = 11.7938(9), b = 3.9858(6), c = 11.6478(7) Å, Z = 4; the space group is Pnma. The positional and thermal parameters, with anisotropic temperature factors, were refined by full-matrix, least-squares calculations to a final R = 0.052.
Sb2Se3 is isostructural with Sb2S3 and Bi2Se3. Each Sb(1) atom is six-coordinated by 2 Se(1), 3 Se(2), 1 Se(3) atoms, in the form of a strongly distorted octahedron, at distances 2.664 to 3.248 Å (P1 polyhedron). The Sb(2) atoms, however, are seven-coordinated by 3Se(l), 2Se(2) and 2Se(3) atoms at distances 2.589 to 3.485 Å (P2 polyhedron). The four Se atoms [2Se(1), 2Se(3)] form a rectangle parallel to (010), which constitutes the base of a tetragonal pyramid whose apex is Se(1). The two remaining Se(2) atoms, together with those of the rectangle, form a triangular prism perpendicular to (010).
Each P1 octahedron is linked to a symmetry-equivalent polyhedron by a common Se(2), Se(2) edge to form a double polyhedron unit, which is further linked to other P1 double polyhedra along the b axis in infinite chains. In an analogous way, two symmetry-related P2 composite polyhedra are linked by a common Se(1), Se(1) edge to form a double polyhedron, which is linked to other double polyhedra along the b axis, resulting again in an infinite chain. Each P1 chain holds together four neighboring parallel P2 chains and each P2 chain in its turn holds together four neighboring parallel P1 chains.