Low chalcocite is monoclinic, space group P21/c, with a unit cell having a = 15.246(4) Å., b = 11.884(2) Å, c = 13.494(3) Å, ß = 116.35(1)°, and containing 48 Cu2S. Its structure was solved by the symbolic addition method, using 5155 independent intensity data measured with MoKα radiation on an automatic diffractometer. Refinement in anisotropic mode led to R = 0.086. The structure is based on hexagonal-close-packed framework of sulfur atoms, with copper atoms occupying mainly triangular interstices. Of the 24 different copper atoms, 21 form triangular CuS3 groups, and one is in a distorted CuS4 tetrahedron. Djurleite is monoclinic, space group P21/n, with a unit cell having a = 26.897(6) Å, b = 15.745(3) Å, c = 13.565(3) Å, ß = 90.13(3)°, and containing 8Cu31S16. The structure was solved by extending the known substructure phases by the symbolic addition procedure, using 5686 independent intensity data measured with MoKα radiation. Refinement converged at R = 0.116. The structure is similar in general to the low chalcocite structure, but of the 62 different copper atoms, 52 form triangular groups, 9 form distorted tetrahedral groups, and one is in unique linear twofold coordination. Both structures are derived from the high chalcocite structure (P63/mmc, a = 3.96 Å, c = 6.72 Å, cell content = 2Cu2S) which forms a substructure corresponding to the hexagonal-close-packed sulfur framework, but the details of the copper arrangement are entirely different in the two phases. The average Cu —S bond length in the CuS3 triangles is 2.32 Å in low chalcocite and 2.29 Å in djurleite. The overall average Cu — S distance in the tetrahedra is 2.48 Å, but varies from 2.22 to 2.91 Å. Each copper atom has from 2 to 8 other copper atom neighbors less than 3.0 Å distant, varying up from 2.45 Å through a maximum clustering at about 2.78 Å. Cu — Cu bonding interaction is probably significant but is not clearly understood. © by Akademische Verlagsgesellschaft, Wiesbaden 1979
