Redetermination of the crystal structure of K[BrF4] from single-crystal X-ray diffraction data

Ivlev, S.I.; Kraus, F.

doi:10.1107/S2414314618006466

inorganic compounds

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ISSN: 2414-3146

Volume 3| Part 5| May 2018| x180646

https://doi.org/10.1107/S2414314618006466

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Redetermination of the crystal structure of K[BrF₄] from single-crystal X-ray diffraction data

Sergei I. Ivlev ^a and Florian Kraus ^a ^*

^aFachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35032 Marburg, Germany
^*Correspondence e-mail: f.kraus@uni-marburg.de

Edited by M. Weil, Vienna University of Technology, Austria (Received 12 April 2018; accepted 26 April 2018; online 1 May 2018)

Single crystals of K[BrF₄], potassium tetrafluoridobromate(III), were grown from a solution of KHF₂ in bromine trifluoride. The current report is the first refinement of the crystal structure of K[BrF₄] using single-crystal X-ray diffraction data. In comparison with previous refinements from powder data, the fractional coordinates of the F atom were determined with higher precision, and anisotropic displacement parameters were refined for all atoms. The structure contains square-planar [BrF₄]⁻ anions. The coordination polyhedron of the potassium cation is a square antiprism.

Keywords: crystal structure; potassium; tetrafluoridobromate; redetermination.

CCDC reference: 1839858

Structure description

The first attempt to elucidate the crystal structure of K[BrF₄] was carried out by Siegel using powder X-ray diffraction data (Siegel, 1956 ). He could index the powder pattern in a tetragonal cell, space group I4/mcm, with a = 6.162 (2), c = 11.081 (2) Å, and the [BrF₄]⁻ anion having a tetrahedral configuration. Subsequently, the diffraction data of Siegel were reinterpreted by Sly & Marsh (1957 ). They kept the unit cell but assigned different positions to the atoms within the same group type, yielding a more reasonable square-planar [BrF₄]⁻ anion. This shape of the anion was later confirmed by Edwards and Jones using powder neutron diffraction data [a = 6.17 (1), c = 11.10 (1) Å; Edwards & Jones, 1969 ]. Similar cell parameters were reported later by Chrétien and Bouy using powder X-ray diffraction data (a = 6.162, c = 11.081 Å, no s.u. given; Chrétien & Bouy, 1958 ) and by Popov et al. [powder X-ray diffraction data, a = 6.192 (5), c = 11.108 (7) Å; Popov et al., 1987 ]. Although this was not reported anywhere, we assume that all measurements were performed at room temperature. Here we report our results of the crystal structure determination of K[BrF₄] using single-crystal X-ray diffraction data at 100 K.

The lattice parameters obtained from our diffraction data (Table 1) are in good correspondence with previously published values. The K⁺ cation resides on Wyckoff position 4a (site symmetry 422). The centre of the [BrF₄]⁻ anion is located on Wyckoff position 4d (m.mm), with the F atoms occupying Wyckoff position 16l (..m). The Br—F bond length amounts to 1.8924 (9) Å. This value is typical for the [BrF₄]⁻ anion and is observed in other known tetrafluoridobromates that were investigated earlier by us (Table 2). The F—Br—F angles are 90.02 (3) and 89.98 (5)°, respectively, and are right angles within the 3σ criterion. The nearest K—F distance is 2.7112 (6) Å. The resulting coordination sphere of the potassium cation by fluorine atoms is a square antiprism. The crystal structure of K[BrF₄] and its unit cell is shown in Fig. 1.

Table 1
Experimental details

Crystal data
Chemical formula	K[BrF₄]
M_r	195.01
Crystal system, space group	Tetragonal, I4/mcm
Temperature (K)	100
a, c (Å)	6.0999 (6), 11.0509 (14)
V (Å³)	411.19 (10)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	10.95
Crystal size (mm)	0.23 × 0.15 × 0.13

Data collection
Diffractometer	STOE IPDS 2T
Absorption correction	Numerical (X-RED32 and X-SHAPE; Stoe & Cie, 2017 )
T_min, T_max	0.157, 0.272
No. of measured, independent and observed [I > 2σ(I)] reflections	2822, 214, 198
R_int	0.050
(sin θ/λ)_max (Å⁻¹)	0.742

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.015, 0.032, 1.24
No. of reflections	214
No. of parameters	13
Δρ_max, Δρ_min (e Å⁻³)	0.60, −0.73
Computer programs: WinXpose in X-AREA (Stoe & Cie, 2016 ), Recipe in X-AREA (Stoe & Cie, 2015 ), Integrate in X-AREA (Stoe & Cie, 2018 ), SHELXT2014 (Sheldrick, 2015a ), SHELXL2016 (Sheldrick, 2015b ), DIAMOND (Brandenburg, 2018 ) and publCIF (Westrip, 2010 ).

Table 2
Interatomic distances (Å) in known M tetrafluoridobromates(III) (M = Na, K, Rb, Cs, Ba)

Compound	Br—F	M—F
K[BrF₄] (at 100 K; this work)	1.8924 (9)	2.7112 (6)
Na[BrF₄] (at 100 K; Ivlev et al., 2016 )	1.899 (1)	2.4674 (4)
Rb[BrF₄] (at RT; Ivlev et al., 2015 )	1.932 (8)	2.851 (7)
Cs[BrF₄] (at RT; Ivlev et al., 2013 )	1.94 (7) − 1.97 (4)	2.89 (3) − 3.490 (8)
Ba[BrF₄]₂ (at RT; Ivlev et al., 2014 )	1.801 (4)–1.935 (2)	2.696 (3)–3.376 (3)

Figure 1
The crystal structure of K[BrF₄] in a projection along the a axis. Displacement ellipsoids are shown at the 70% probability level.

Synthesis and crystallization

Potassium tetrafluoridobromate(III) was synthesized using potassium hydrogen fluoride KHF₂ (0.20 g, 2.6 mmol, 1 eq.) and an excess of liquid bromine trifluoride (1 ml, 2.8 g, 20.4 mmol, 8.0 eq.). The reaction was carried out in an FEP vessel (perfluorinated ethylene propylene copolymer) at 393 K. After complete dissolution of KHF₂, the resulting solution was allowed to cool down to room temperature. Within two hours, large colourless crystals were observed, which were picked directly out of liquid BrF₃.

Refinement

Details of data collection and structure refinement are given in Table 1.

Structural data

CCDC reference: 1839858

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314618006466/wm4077sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314618006466/wm4077Isup2.hkl

checkCIF report

Computing details top

Data collection: WinXpose in X-AREA (Stoe & Cie, 2016); cell refinement: Recipe in X-AREA (Stoe & Cie, 2015); data reduction: Integrate in X-AREA (Stoe & Cie, 2018); program(s) used to solve structure: SHELXT2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg, 2018); software used to prepare material for publication: publCIF (Westrip, 2010).

Potassium tetrafluoridobromate(III) top

Crystal data top

K⁺·BrF₄⁻	Melting point: 533 K
M_r = 195.01	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4/mcm	Cell parameters from 3833 reflections
a = 6.0999 (6) Å	θ = 3.7–32.1°
c = 11.0509 (14) Å	µ = 10.95 mm⁻¹
V = 411.19 (10) Å³	T = 100 K
Z = 4	Block, colorless
F(000) = 360	0.23 × 0.15 × 0.13 mm
D_x = 3.150 Mg m⁻³

Data collection top

STOE IPDS 2T diffractometer	214 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	198 reflections with I > 2σ(I)
Plane graphite monochromator	R_int = 0.050
Detector resolution: 6.67 pixels mm^-1	θ_max = 31.8°, θ_min = 3.7°
rotation method, ω scans	h = −9→9
Absorption correction: numerical (X-RED32 and X-SHAPE; Stoe & Cie, 2017)	k = −8→9
T_min = 0.157, T_max = 0.272	l = −16→16
2822 measured reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0152P)² + 0.2331P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.015	(Δ/σ)_max < 0.001
wR(F²) = 0.032	Δρ_max = 0.60 e Å⁻³
S = 1.24	Δρ_min = −0.73 e Å⁻³
214 reflections	Extinction correction: SHELXL2016 (Sheldrick, 2015b), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
13 parameters	Extinction coefficient: 0.0087 (11)
0 restraints

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Br1	0.500000	0.000000	0.500000	0.00790 (12)
K1	0.500000	0.500000	0.250000	0.01054 (16)
F1	0.65508 (11)	0.15508 (11)	0.37889 (7)	0.0138 (2)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.00811 (14)	0.00811 (14)	0.00749 (15)	0.00046 (10)	0.000	0.000
K1	0.0108 (2)	0.0108 (2)	0.0101 (3)	0.000	0.000	0.000
F1	0.0146 (3)	0.0146 (3)	0.0122 (4)	−0.0008 (4)	0.0030 (2)	0.0030 (2)

Geometric parameters (Å, º) top

Br1—F1	1.8923 (9)	K1—F1^viii	2.7112 (6)
Br1—F1ⁱ	1.8924 (9)	K1—F1^ix	2.7112 (6)
Br1—F1ⁱⁱ	1.8924 (9)	K1—F1^x	2.7112 (6)
Br1—F1ⁱⁱⁱ	1.8924 (9)	K1—F1	2.7112 (6)
K1—F1^iv	2.7112 (6)	K1—K1^xi	4.3133 (6)
K1—F1^v	2.7112 (6)	K1—K1^xii	4.3133 (6)
K1—F1^vi	2.7112 (6)	K1—K1^xiii	4.3133 (6)
K1—F1^vii	2.7112 (6)	K1—K1^x	4.3133 (6)

F1—Br1—F1ⁱ	90.02 (5)	F1^viii—K1—K1^xi	142.700 (14)
F1—Br1—F1ⁱⁱ	89.98 (5)	F1^ix—K1—K1^xi	37.300 (14)
F1ⁱ—Br1—F1ⁱⁱ	180.0	F1^x—K1—K1^xi	72.421 (19)
F1—Br1—F1ⁱⁱⁱ	180.0	F1—K1—K1^xi	107.579 (19)
F1ⁱ—Br1—F1ⁱⁱⁱ	89.98 (5)	F1^iv—K1—K1^xii	37.300 (14)
F1ⁱⁱ—Br1—F1ⁱⁱⁱ	90.02 (5)	F1^v—K1—K1^xii	142.700 (14)
F1^iv—K1—F1^v	144.84 (4)	F1^vi—K1—K1^xii	107.579 (19)
F1^iv—K1—F1^vi	139.16 (4)	F1^vii—K1—K1^xii	72.421 (19)
F1^v—K1—F1^vi	73.977 (14)	F1^viii—K1—K1^xii	37.300 (14)
F1^iv—K1—F1^vii	73.977 (14)	F1^ix—K1—K1^xii	142.700 (14)
F1^v—K1—F1^vii	139.16 (3)	F1^x—K1—K1^xii	107.579 (19)
F1^vi—K1—F1^vii	74.60 (3)	F1—K1—K1^xii	72.421 (19)
F1^iv—K1—F1^viii	74.60 (3)	K1^xi—K1—K1^xii	180.0
F1^v—K1—F1^viii	116.61 (3)	F1^iv—K1—K1^xiii	107.579 (19)
F1^vi—K1—F1^viii	73.977 (15)	F1^v—K1—K1^xiii	107.579 (19)
F1^vii—K1—F1^viii	78.20 (4)	F1^vi—K1—K1^xiii	37.300 (14)
F1^iv—K1—F1^ix	116.61 (3)	F1^vii—K1—K1^xiii	37.300 (14)
F1^v—K1—F1^ix	74.60 (3)	F1^viii—K1—K1^xiii	72.421 (19)
F1^vi—K1—F1^ix	78.20 (4)	F1^ix—K1—K1^xiii	72.421 (19)
F1^vii—K1—F1^ix	73.977 (15)	F1^x—K1—K1^xiii	142.700 (14)
F1^viii—K1—F1^ix	144.84 (4)	F1—K1—K1^xiii	142.699 (15)
F1^iv—K1—F1^x	73.977 (14)	K1^xi—K1—K1^xiii	90.0
F1^v—K1—F1^x	78.20 (4)	K1^xii—K1—K1^xiii	90.0
F1^vi—K1—F1^x	144.84 (4)	F1^iv—K1—K1^x	72.421 (19)
F1^vii—K1—F1^x	116.61 (3)	F1^v—K1—K1^x	72.421 (19)
F1^viii—K1—F1^x	139.16 (3)	F1^vi—K1—K1^x	142.700 (14)
F1^ix—K1—F1^x	73.977 (15)	F1^vii—K1—K1^x	142.700 (14)
F1^iv—K1—F1	78.20 (4)	F1^viii—K1—K1^x	107.579 (19)
F1^v—K1—F1	73.978 (14)	F1^ix—K1—K1^x	107.579 (19)
F1^vi—K1—F1	116.61 (3)	F1^x—K1—K1^x	37.300 (14)
F1^vii—K1—F1	144.84 (4)	F1—K1—K1^x	37.301 (14)
F1^viii—K1—F1	73.977 (14)	K1^xi—K1—K1^x	90.0
F1^ix—K1—F1	139.16 (4)	K1^xii—K1—K1^x	90.0
F1^x—K1—F1	74.60 (3)	K1^xiii—K1—K1^x	180.0
F1^iv—K1—K1^xi	142.700 (14)	Br1—F1—K1^x	125.809 (18)
F1^v—K1—K1^xi	37.300 (14)	Br1—F1—K1	125.809 (18)
F1^vi—K1—K1^xi	72.421 (19)	K1^x—F1—K1	105.40 (3)
F1^vii—K1—K1^xi	107.579 (19)

Symmetry codes: (i) x, y, −z+1; (ii) −x+1, −y, z; (iii) −x+1, −y, −z+1; (iv) −y+1/2, x−1/2, −z+1/2; (v) −y+1, x, z; (vi) −x+1, −y+1, z; (vii) x−1/2, y+1/2, −z+1/2; (viii) y, −x+1, z; (ix) y+1/2, −x+3/2, −z+1/2; (x) −x+3/2, −y+1/2, −z+1/2; (xi) −x+3/2, −y+3/2, −z+1/2; (xii) −x+1/2, −y+1/2, −z+1/2; (xiii) −x+1/2, −y+3/2, −z+1/2.

Interatomic distances (Å) in known M tetrafluoridobromates(III) (M = Na, K, Rb, Cs, Ba) top

Compound	Br—F	M—F
K[BrF₄] (at 100 K; this work)	1.8924 (9)	2.7112 (6)
Na[BrF₄] (at 100 K; Ivlev et al., 2016)	1.899 (1)	2.4674 (4)
Rb[BrF₄] (at RT; Ivlev et al., 2015)	1.932 (8)	2.851 (7)
Cs[BrF₄] (at RT; Ivlev et al., 2013)	1.94 (7) - 1.97 (4)	2.89 (3) - 3.490 (8)
Ba[BrF₄]₂ (at RT; Ivlev et al., 2014)	1.801 (4) - 1.935 (2)	2.696 (3) - 3.376 (3)

Acknowledgements

We are grateful to Dr Harms (Marburg) for X-ray measurement time.

Funding information

We thank the DFG for very generous funding.

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