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

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 β-BaTbF₆ and other representatives of the M^IIMF₆ family allows the singular crystal-chemical properties of some fluoroterbates to be emphasized.

S1. Comment

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S2. Experimental

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S3. Refinement

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Computing details

For both compounds, program(s) used to refine structure: Fullprof; molecular graphics: CaRIne (C. Boudias & D. Monceau, 1989).

Figures

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(CaTbF6data) calcium terbium hexafluoride

Crystal data

CaTbF6	Z = 2
Mr = 312.99	Dx = 4.85 Mg m^−3
Tetragonal, P42/m	Thermal neutron radiation, λ = 1.2251 Å
Hall symbol: -P 4c	T = 293 K
a = 5.2696 (1) Å	white
c = 7.7105 (2) Å	cylinder, ? × ? × ? mm
V = 214.11 (1) Å^3	Specimen preparation: Prepared at 900 K

Data collection

3T2 diffractometer	Data collection mode: reflection
Radiation source: thermal neutron	Scan method: step
Specimen mounting: cylindrical container	2θmin = 6°, 2θmax = 126°, 2θstep = 0.05°

Refinement

Refinement on integrated intensities	Profile function: pseudo-Voigt
Rp = 0.116	9 parameters
Rwp = 0.110	1/[Yi + σ(Yi)]
Rexp = 0.057
χ^2 = 3.686	Background function: interpolated from selected point
2395 data points	Preferred orientation correction: ···

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Ca	0	0	0.5	1.85 (5)*
Tb	0.5	0.5	0.75	−0.03 (2)*
F1	0.2103 (2)	0.2550 (2)	0.3184 (1)	1.54 (2)*
F2	0.3440 (4)	0.6769 (4)	0.5	1.18 (3)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
?

(CdTbF6data) calcium terbium hexafluoride

Crystal data

CdTbF6	Z = 2
Mr = 385.33	Dx = 6.18 Mg m^−3
Tetragonal, P42/m	Cu Kαlpha radiation, λ = 1.54056 Å
Hall symbol: -P 4c	T = 293 K
a = 5.18770 (2) Å	white
c = 7.69451 (3) Å	flat sheet, ? × ? × ? mm
V = 207.08 (1) Å^3	Specimen preparation: Prepared at 830 K

Data collection

Phillips X-Pert Pro diffractometer	Data collection mode: reflection
Radiation source: Sealed X-ray tube	Scan method: step
Specimen mounting: Bragg-Brentano geometry with plate sample holder	2θmin = 5°, 2θmax = 140°, 2θstep = 0.012°

Refinement

Refinement on integrated intensities	Profile function: pseudo-Voigt
Rp = 0.158	8 parameters
Rwp = 0.185	1/[Yi + σ(Yi)]
Rexp = 0.155
χ^2 = 4.884	Background function: interpolated from selected point
11251 data points	Preferred orientation correction: ···

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cd	0	0	0.5	1.67 (4)*
Tb	0.5	0.5	0.75	1.39 (4)*
F1	0.200 (1)	0.262 (1)	0.3224 (8)	2.1 (1)*
F2	0.351 (3)	0.693 (2)	0.5	2.1 (1)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
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