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Dipotassium trizirconium oxide dodecafluoride, K2Zr3OF12, obtained by microwave-assisted hydro­thermal synthesis, crystallizes in the trigonal space group R\overline 3m (No. 166) and is isostructural with Tl2Zr3OF12. The structure was determined from X-ray powder diffraction data and is described in terms of fluorine- or oxy­gen-centered cation polyhedra and consists of [F12O2KZr6] and [F12K3Zr6] layers connected by Zr4+ cations.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536803018567/br6110sup1.cif
Contains datablocks global, I

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S1600536803018567/br6110Isup2.rtv
Contains datablock I

Key indicators

  • Powder X-ray study
  • T = 293 K
  • R factor = 0.000
  • wR factor = 0.000
  • Data-to-parameter ratio = 18.1

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Comment top

Because of their potential activity in non-linear optics or catalysis, attention has been paid recently to fluoride salts, fluoride borates (Becker, 1998; Dorozhkin et al., 1981), fluoride carbonates (Mercier et al., 1997), fluoride sulfates (Wickleder, 1999), fluoride phosphates (Zhizhin et al., 2001). The object of our work was to investigate the crystallization of zirconium fluoride silicates from hydrothermal solutions under microwave heating. No fluoride silicate was found in the KOH–SiO2–ZrF4–H2O system and only one oxide fluoride was obtained. This phase, K2Zr3OF12, is isostructural with both Tl2Zr3OF12 (Mansouri & Avignant, 1984) and Rb2Zr3OF12 (Koller & Muller, 2002). The structure of K2Zr3OF12 was determined by powder diffraction. The X-ray diffraction pattern is given Fig. 1. Calculated bond valences (Brese & O'Keeffe, 1991) show that the interatomic distances are satisfactory and in agreement with bibliographic data. The isotropic atomic displacement parameters are also acceptable. The structure of K2Zr3OF12 consists of ZrOF7 and KF6 polyhedra. O atoms lie at the common vertex of three edge-sharing ZrOF7 polyhedra. These polyhedra, linked by corners or edges, build hexameric Zr3OF18 units which share edges in order to form [Zr6O4F30] polyanions. The polyanions, linked by corners, build infinite [ZrOF12] double layers running perpendicular to the c axis. The structure can be also described in terms of fluorine- or oxygen-centered cation polyhedra (Fig. 2a). In K2Zr3OF12, the F4 atoms adopt a twofold coordination. All other F atoms, together with O atoms, are in a triangular environment and form [FK2Zr], [FKZr2] and [OZr3] entities. The triangular groups [F1KZr2] (green), sharing Zr–Zr edges, form [F1KZr]2 dimers. These dimers, connected by K atoms, build infinite chains along the [100], [010] and [110] directions. The resulting [F16KZr6] layers (Fig. 2 b) include F4 and O atoms, which form [F43Zr3] triangular cycles and [OZr3] triangular entities (red) (Fig. 2c); they build [F16F46O2Zr6K1] layers perpendicular to the c axis. [F2K2K3Zr] and [F3K3Zr2] entities, purple and yellow, respectively, are linked by corners and define cages of six triangles (4 × F2 and 2 × F3). These cages, connected one to each other, build [F26F36K3Zr6] layers parallel to the ab plane (Fig. 2 d). The [F16F46O2Zr6K] and [F26F36K3Zr6] sheets which alternate along the c direction, are linked through Zr atoms.

Experimental top

A powder sample of K2Zr3OF12 was prepared from 0.6688 g of ZrF4 and 10 ml of a 0.4 M KOH solution. The reaction mixture was then heated for 1 h at T = 463 K (P = 12 10 5 Pa) in a CEM microwave oven (MDS 2100) using a Teflon-lined autoclave. The compound was then washed with acetone and dried in air. The product was characterized by X-ray powder diffraction on a Siemens Brucker D8 diffractometer. Thermal analysis was performed with a DTA–TGA TA Instrument 260 (heating rate 10 K min−1; argon atmosphere). Above 908 K, K2Zr3OF12 decomposes and undergoes hydrolysis to give ZrO2 and K3ZrF7. Owing to the absence of IR lines around 3300 and 1600 cm−1, the F–OH substitution, expected from the preparation mode, is excluded.

Refinement top

Reflection positions were determined by means of the EVA program (available in the Socabim PC software package DIFFRAC-AT supplied by Siemens, derivative method) after Kα2 radiation stripping. Auto-indexing of 13 intense reflections by using the McMaille program (Le Bail, 2002) leads to an hexagonal cell similar to that of Tl2Zr3OF12. The atomic positions of Tl2Zr3OF12 were used as a starting model.

Computing details top

Program(s) used to refine structure: FULLPROF (Rodriguez-Carvajal, 1998); molecular graphics: DIAMOND (Brandenburg, 2001); software used to prepare material for publication: FULLPROF (Rodriguez-Carvajal, 1998).

Figures top
[Figure 1] Fig. 1. Final profile refinement of K2Zr3OF12: observed (circle), calculated (line), and difference (bottom) profiles of X-ray diffraction data. Vertical bars are related to the calculated Bragg reflection positions. The first peak (near 2θ = 9.2°) is not included in final refinement due to its high asymmetry.
[Figure 2] Fig. 2. The structure of K2Zr3OF12.
Zirconium potassium oxide fluoride top
Crystal data top
K2Zr3OF12Z = 6
Mr = 595.85F(000) = 1638
Trigonal, R3mDx = 4.016 Mg m3
Hall symbol: -R 3 2"Cu Kα radiation, λ = 1.54178 Å
a = 7.6887 (3) ÅT = 293 K
c = 28.870 (1) Åwhite
V = 1478.0 (2) Å3?, ? × ? × ? mm
Data collection top
D8 Bruker
diffractometer
Scan method: step
None monochromator2θmin = 11°, 2θmax = 100°, 2θstep = 0.02°
Specimen mounting: packed powder pellet
Refinement top
Refinement on InetExcluded region(s): 5.00 11.00°
Rp = 0.12Profile function: pseudo-Voigt
Rwp = 0.13926 parameters
Rexp = 0.0570 restraints
RBragg = 0.0660 constraints
χ2 = 5.905
4751 data pointsBackground function: linear interpolation
Crystal data top
K2Zr3OF12V = 1478.0 (2) Å3
Mr = 595.85Z = 6
Trigonal, R3mCu Kα radiation, λ = 1.54178 Å
a = 7.6887 (3) ÅT = 293 K
c = 28.870 (1) Å?, ? × ? × ? mm
Data collection top
D8 Bruker
diffractometer
Scan method: step
Specimen mounting: packed powder pellet2θmin = 11°, 2θmax = 100°, 2θstep = 0.02°
Refinement top
Rp = 0.12χ2 = 5.905
Rwp = 0.1394751 data points
Rexp = 0.05726 parameters
RBragg = 0.0660 restraints
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
K10000.021 (1)*
K2000.50.021 (1)*
K3000.1364 (2)0.0211 (11)*
Zr0.51535 (9)0.51535 (9)0.06227 (5)0.0110 (4)*
F10.3376 (7)000.0129 (9)*
F20.1473 (4)0.1473 (4)0.2019 (2)0.0129 (9)*
F30.1574 (4)0.1574 (4)0.9233 (2)0.0129 (9)*
F40.2214 (4)0.2214 (4)0.0727 (2)0.0129 (9)*
O000.2830 (4)0.0129 (9)*
Geometric parameters (Å, º) top
K1—F1i2.595 (5)Zr—Ov2.044 (2)
K2—F2ii2.679 (4)Zr—F4v2.139 (3)
K3—F3iii2.711 (5)Zr—F4vi2.139 (3)
K3—F2iv2.726 (6)Zr—F1vii2.198 (2)
K3—F22.726 (6)Zr—F1vi2.198 (2)
Zr—F2v1.997 (6)Zr—F3viii2.237 (3)
Zr—Ov2.044 (2)Zr—F3ix2.237 (3)
Zr—Ov2.044 (2)
F1—K1—F3126.69 (12)F2—Zr—O99.1 (4)
F1—K1—F390.0F2—Zr—F482.5 (2)
F3—K1—F3106.6 (2)O—Zr—F4143.1 (2)
F3—K1—F3180.0F4—Zr—F473.8 (4)
F2—K2—F2106.7 (2)F2—Zr—F1145.4 (2)
F2—K2—F4123.6 (2)O—Zr—F187.0 (3)
F2—K2—F496.6 (2)F4—Zr—F173.1 (2)
F4—K2—F4180.000 (1)F4—Zr—F1112.5 (2)
F4—K2—F4130.7 (2)F1—Zr—F168.3 (4)
F4—K2—F4130.7 (2)F2—Zr—F378.5 (2)
F4—K2—F449.3 (2)O—Zr—F369.8 (2)
F4—K2—F4130.7 (2)F4—Zr—F3144.7 (3)
F3—K3—F384.8 (2)F4—Zr—F374.5 (2)
F3—K3—F2175.4 (3)F1—Zr—F3134.6 (2)
F3—K3—F298.6 (2)F1—Zr—F371.8 (2)
F2—K3—F277.8 (3)F3—Zr—F3129.1 (4)
Symmetry codes: (i) x+y, x, z; (ii) xy2/3, x1/3, z+2/3; (iii) y, x+y, z+1; (iv) y, xy, z; (v) x+2/3, y2/3, z+1/3; (vi) x+y+1, x, z; (vii) xy, x1, z; (viii) y+1, x+y, z+1; (ix) xy, x1, z+1.

Experimental details

Crystal data
Chemical formulaK2Zr3OF12
Mr595.85
Crystal system, space groupTrigonal, R3m
Temperature (K)293
a, c (Å)7.6887 (3), 28.870 (1)
V3)1478.0 (2)
Z6
Radiation typeCu Kα, λ = 1.54178 Å
Specimen shape, size (mm)?, ? × ? × ?
Data collection
DiffractometerD8 Bruker
diffractometer
Specimen mountingPacked powder pellet
Data collection mode?
Scan methodStep
2θ values (°)2θmin = 11 2θmax = 100 2θstep = 0.02
Refinement
R factors and goodness of fitRp = 0.12, Rwp = 0.139, Rexp = 0.057, RBragg = 0.066, χ2 = 5.905
No. of data points4751
No. of parameters26

Computer programs: FULLPROF (Rodriguez-Carvajal, 1998), DIAMOND (Brandenburg, 2001).

Selected bond lengths (Å) top
K1—F1i2.595 (5)Zr—Ov2.044 (2)
K2—F2ii2.679 (4)Zr—F4v2.139 (3)
K3—F3iii2.711 (5)Zr—F4vi2.139 (3)
K3—F2iv2.726 (6)Zr—F1vii2.198 (2)
K3—F22.726 (6)Zr—F1vi2.198 (2)
Zr—F2v1.997 (6)Zr—F3viii2.237 (3)
Zr—Ov2.044 (2)Zr—F3ix2.237 (3)
Zr—Ov2.044 (2)
Symmetry codes: (i) x+y, x, z; (ii) xy2/3, x1/3, z+2/3; (iii) y, x+y, z+1; (iv) y, xy, z; (v) x+2/3, y2/3, z+1/3; (vi) x+y+1, x, z; (vii) xy, x1, z; (viii) y+1, x+y, z+1; (ix) xy, x1, z+1.
 

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