THE CRYSTAL-STRUCTURE OF SPANGOLITE, A COMPLEX COPPER-SULFATE SHEET MINERAL

The crystal structure of spangolite, Cu6Al(SO4)(OH)12Cl.3H2O, trigonal , a = 8.254(4) angstrom, c = 14.354(8) angstrom, V = 846.8(8) angstrom 3, space group = P31c, has been solved by direct methods and refined t o an R index of 6.5% using MoKalpha X-ray data. There are two distinct Cu positions, and each Cu2+ cation is coordinated by six anions in [4 + 2]-distorted octahedral arrangements typical of the Jahn-Teller-typ e distortion characteristic of divalent [6]Cu. There is one distinct S position coordinated by a very regular tetrahedral arrangement of O a nions, and one distinct Al position coordinated by a fairly regular oc tahedral arrangement of O anions. The Cl anion is only bonded to the C u2+ cations. The structure consists of an edge-sharing sheet of Cuphi6 and Alphi6 octahedra, decorated on one side by SO, tetrahedra. The Cu phi6 octahedra are associated together in edge-sharing trimers lying o n threefold rotation axes; the sulfate tetrahedron links to the centra l anion on one side of this trimer. These clusters link outward by sha ring edges with Alphi6 octahedra that lie on adjacent threefold axes, producing a continuous Mphi2 sheet. These sheets then link along the c -axis by H-bonding between OH and H2O anions of one sheet and sulfate O atoms of the adjacent sheet.