The structure of Cu4Bi4S9and its relation to the structures of covellite, CuS and bismuthinite, Bi2S3

The orthorhombic unit cell of Cu 4 Bi 4 S 9 crystals has dimensions: a = 11.589(5), b = 32.05(1), c = 3.951(5) Å; space group Pbnm , and Z = 4. The structure, which has been determined with the symbolic addition procedure, contains, sulfur-sulfur bonds in a form of S 2 groups, as predicted from the valence rule with S–S distance of 2.095(17) Å. The structure can be described as an alternate stacking of Cu-S sheets and Bi-S slabs, parallel to (010). The Cu-S sheet is highly corrugated and built of links of four- and three-coordinated copper atoms which are closely related to those in the covellite structure. The links are, in fact, joined together by S–S bonds. The three-coordinated copper atom is not in the plane formed by three sulfur atoms but displaced from the plane by 0.48(1) Å; mean Cu–S distance is 2.25 Å. The Bi-S slabs consist of links of Bi-S polyhedra which are, in turn, closely related to those of the bismuthinite structure. The above feature of the structure thus offers a new example of sulfosalt structure which consists of fragments of two different kinds of simpler sulfide structures.