Abstract

Synthetic chukhrovite, Ca4AlSi(SO4)F13 · 12H2O crystallizes in the cubic space group Fd3, with a = 16.710 (2)Å and Z = 8. The structure was refined to Rw = 0.028 and R = 0.025, using 481 nonzero reflections.

Al and Si are statistically distributed at the same site, M [16(d)], which is surrounded by six fluorine atoms to form the octahedral group MF6. The remaining fluoride ion is surrounded by a tetrahedron of Ca ions [F(1)–Ca = 2.411Å] as in fluorite. The overall coordination of Ca is seven with a geometry corresponding to that of a monocapped octahedron. Each comer of the MF6 octahedron is linked to a Ca coordination polyhedron and each Ca polyhedron shares three comers with three different MF6 octahedra. The SO4 ion is surrounded by 12 water molecules, all of which are hydrogen-bonded to SO4 oxygens. The most unusual feature of this hydration is that all four faces of the SO4 ion are linked to faces of Ca polyhedra via hydrogen bonding.

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