ALBERT

Description: A bstract The crystal structure of mammothite, Pb 6 Cu 4 AlSbO 2 (SO 4 ) 2 Cl 4 (OH) 16 , is monoclinic in acentric space group C 2, with a 18.959(4), b 7.3398(19), c 11.363(3) Å, β 112.428(9){ring}, V 1461.6(1.0) Å 3 , and Z = 2. It has been refined to an R index of 0.019 on the basis of 3878 observed reflections. There are three crystallographically distinct Pb sites with two different co-ordinations: [Pb1O 8 Cl 1 ] is a mono-capped square antiprism polyhedron, while [Pb21O 7 Cl 2 ] and [Pb22O 7 Cl 2 ] are tri-capped trigonal prisms. Both Cu 2+ sites have distorted [4 + 2] octahedral coordination due to the Jahn-Teller effect. The Al and Sb sites are regular-octahedral co-ordination with oxygen atoms. The [SO 4 ] tetrahedron is quite distorted, with S–O bond lengths varying from 1.45 to 1.52 Å and subtended O–S–O angles varying from 106 to 113{ring}. In the structure there are eight (OH) – anions. All eight H atoms pfu were located, and it is these structure sites that reduce the symmetry from centric to acentric. Although mammothite is classified as a framework structure, it has a distinct layering. There are two layer types in the mammothite structure that parallel (001). There are three octahedrally coordinated sites; two are occupied by Cu atoms and one by an Al atom, in the octahedral layer. The tetragonal dipyramids [CuØ 6 ] are linked forming ‘olivine-like’ chains parallel to the b -axis. The second layer, termed the cross-linked layer, has three [PbØ 9 ] polyhedra with shared edges forming chains parallel to the b -axis, like the [CuØ 6 ] tetragonal dipyramids. These chains are cross-linked by edge-sharing [SbO 6 ] octahedra and decorated with [SO 4 ] groups. The H atoms are in ‘holes’ within both layers.