Acta Crystallographica Section B

Structural Science

Volume 61, Part 1 (February 2005)

research papers

Acta Cryst. (2005). B61, 1-10 [ doi:10.1107/S0108768104026928 ]

Anti-KSbF₆ structure of CaTbF₆ and CdTbF₆: a confirmation of the singular crystal chemistry of Tb⁴⁺ in fluorides

M. Josse, M. Dubois, M. El-Ghozzi, J. Cellier and D. Avignant

Abstract: The crystal structures of two new tetravalent terbium fluorides, CaTbF₆ and CdTbF₆, have been determined from X-ray and neutron powder diffraction data. The title compounds exhibit an anti-KSbF₆ structure, the three-dimensional framework of which is built of [TbF₆]^2- chains of edge-sharing dodecahedra further linked, by sharing corners, to isolated [MF₆]^4- octahedra (M = Ca, Cd). The mechanism of the anionic sublattice rearrangement when going from KSbF₆ to CaTbF₆ is described and related to a simple cubic fluoride-ion packing. Comparison with the crystal structures of [beta] -BaTbF₆ and other representatives of the M^IIM $^{\prime \rm IV}$ F₆ family allows the singular crystal-chemical properties of some fluoroterbates to be emphasized.

Keywords: tetravalent terbium fluoride; X-ray powder diffraction; neutron powder diffraction; crystal chemistry.