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The structure of dipotassium tantalum heptafluoride, K2TaF7, was optimized by energy minimization in the solid state using a plane-waves DFT (density functional theory) computation for which the lattice parameters were obtained by the Le Bail technique from synchrotron X-ray powder diffraction data collected at 993 K. Owing to the sample's corrosiveness, it had to be loaded in a thin-walled Pt capillary. It was found that the structure corresponds to that of the β-K2TaF7 phase. The Ta atoms in the TaF7 polyhedra are sevenfold coordinated by fluorine atoms positioned within 1.977–2.007 Å. The K atoms are surrounded by eleven (K1) or eight (K2) fluorine atoms. Every F atom in the structure is surrounded by three K atoms. The F...K contact distances vary from 2.57 to 3.32 Å. It is suggested that solid-state DFT methods may, in many cases, provide an alternative tool to standard Rietveld refinements for structure determination.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0021889808005876/db5039sup1.cif
Contains datablocks global, I

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0021889808005876/db5039Isup2.rtv
Contains datablock I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0021889808005876/db5039Isup3.hkl
Contains datablock I

Computing details top

Program(s) used to refine structure: FULLPROF; molecular graphics: Diamond; software used to prepare material for publication: PLATON.

Figures top
[Figure 1]
[Figure 2]
[Figure 3]
Dipotassium heptafluorotantalate(V) top
Crystal data top
F7Ta·2(K)V = 727.84 (9) Å3
Mr = 392.15Z = 4
Orthorhombic, PNMAX-ray radiation, λ = 0.398230 Å
Hall symbol: -P 2ac 2nT = 993 K
a = 10.0731 (7) Åwhite
b = 5.9456 (4) Åcylinder, ? × ? × ? mm
c = 12.1527 (9) Å
Data collection top
'ESRF, ID31'
diffractometer
Data collection mode: transmission
Radiation source: synchrotron2θmin = 4.006°, 2θmax = 14.989°, 2θstep = 0.009°
Specimen mounting: Pt capillary
Refinement top
Rp = 9.646Profile function: Lorentzian
Rwp = 13.36110 parameters
Rexp = 5.5790 restraints
RBragg = 18.477
χ2 = NOT FOUNDBackground function: linear approximation
1203 data pointsPreferred orientation correction: none
Crystal data top
F7Ta·2(K)V = 727.84 (9) Å3
Mr = 392.15Z = 4
Orthorhombic, PNMAX-ray radiation, λ = 0.398230 Å
a = 10.0731 (7) ÅT = 993 K
b = 5.9456 (4) Åcylinder, ? × ? × ? mm
c = 12.1527 (9) Å
Data collection top
'ESRF, ID31'
diffractometer
Data collection mode: transmission
Specimen mounting: Pt capillary2θmin = 4.006°, 2θmax = 14.989°, 2θstep = 0.009°
Refinement top
Rp = 9.646χ2 = NOT FOUND
Rwp = 13.3611203 data points
Rexp = 5.57910 parameters
RBragg = 18.4770 restraints
Special details top

Experimental. The powder was loaded into a X·X mm Pt capillary with wall thickness of Y·Y mm. The sample was heated by a hot air blower mounted perpendicular with respect to the capillary.

Refinement. The structure was refined by geometry optimization done by cell energy minimization. This is why no estimated standard deviations are given for atomic coordinates.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
ta10.242600.250000.131500.074 (4)*
k10.128100.750000.950600.25 (2)*
k20.463800.250000.828200.25 (2)*
f10.359500.033600.054800.147 (17)*
f20.092700.033400.145900.147 (17)*
f30.300000.047700.252300.147 (17)*
f40.163400.250000.979900.147 (17)*

Experimental details

Crystal data
Chemical formulaF7Ta·2(K)
Mr392.15
Crystal system, space groupOrthorhombic, PNMA
Temperature (K)993
a, b, c (Å)10.0731 (7), 5.9456 (4), 12.1527 (9)
V3)727.84 (9)
Z4
Radiation typeX-ray, λ = 0.398230 Å
µ (mm1)?
Specimen shape, size (mm)Cylinder, ? × ? × ?
Data collection
Data collection method'ESRF, ID31'
Specimen mountingPt capillary
Data collection modeTransmission
Scan method?
2θ values (°)2θmin = 4.006 2θmax = 14.989 2θstep = 0.009
Refinement
R factors and goodness of fitRp = 9.646, Rwp = 13.361, Rexp = 5.579, RBragg = 18.477, χ2 = NOT FOUND
No. of data points1203
No. of parameters10

Computer programs: FULLPROF, Diamond, PLATON.

 

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