Acta Cryst. (2009). E65, i16-i17  [ doi:10.1107/S1600536809005054 ]

Rietveld refinement of Sr₅(AsO₄)₃Cl from high-resolution synchrotron data

A. M. T. Bell, C. M. B. Henderson, R. F. Wendlandt and W. J. Harrison

Abstract: The apatite-type compound, pentastrontium tris[arsenate(V)] chloride, Sr₅(AsO₄)₃Cl, has been synthesized by ion exchange at high temperature from a synthetic sample of mimetite [Pb₅(AsO₄)₃Cl] with SrCO₃ as a by-product. The results of the Rietveld refinement, based on high resolution synchrotron X-ray powder diffraction data, show that the title compound crystallizes in the same structure as other halogenoapatites with general formula A₅(YO₄)₃X (A = divalent cation, Y = pentavalent cation, and X = F, Cl or Br) in the space group P6₃/m. The structure consists of isolated tetrahedral AsO₄^3- anions (the As atom and two O atoms have m symmetry), separated by two crystallographically independent Sr²⁺ cations that are located on mirror planes and threefold rotation axes, respectively. One Sr atom is coordinated by nine O atoms and the other by six. The chloride anions (site symmetry ) are at the 2a sites and are located in the channels of the structure.

Online 21 February 2009

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