Structural study of cadmium hydroxide sulfates. VI. The layer structure of Cd_4SO_4(OH)_(6.)1.5H_2O studied from X-ray powder and single-crystal diffraction data

摘要

The crystal structure of the layered cadmium hydroxide sulfate Cd_4SO_4(OH)_(6.)1.5H_2O has been solved from X-ray powder diffraction data. The compound crystallizes with hexagonal symmetry, α = 9.145(l) A, c=15.099(3) A, V=1093.5A~3, Z = 4, space group P6_3. Due to the unusual environment of one cadmium atom and to the fact that a suitable thin tabular crystal could be found later, a single-crystal X-ray diffraction experiment was also carried out. In both cases the structure was solved applying direct-methods. The refinements converged to the residual factors R_(wp) = 0.152 and R_F=0.059 from the powder data and R_1 =0.058 and wR = 0.165 for the single crystal data case. The structure is built from brucite-type layers based on CdO_6 octahedra, in which one-seventh of the octahedral sites are empty. Directly above and below these empty sites, two additional octahedrically coordinated Cd atoms are located. The crystal chemistry of the cadmium hydroxide sulfate family is discussed.