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

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

Université Blaise Pascal, Laboratoire des Matériaux Inorganiques, UMR 6002 CNRS, 24 Avenue des Landais, 63177 Aubiere, France.

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(II)M('IV)F6 family allows the singular crystal-chemical properties of some fluoroterbates to be emphasized.

Published 20 January 2005 in Acta Crystallogr B, 61: 1-10.
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