X-ray powder diffraction study of synthetic Palmierite, K2Pb(SO4)2

The crystal structure of the layered cadmium hydroxide sulfate Cd4SO4(OH)6.1.5H2O has been solved from X-ray powder diffraction data. The compound crystallizes with hexagonal symmetry, a=9.145(1) A, c= 15.099(3) A, V=1093.5A3 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 Rwp = 0.152 and Rp= 0.059 from the powder data and R1=0.058 and wR=0.165 for the single crystal data case. The structure is built from brucite-type layers based on CdO6 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.