Rerefinement of the crystal structure of BiF₅

The crystal structure of bis­muth penta­fluoride, BiF₅, was rerefined from single-crystal data. BiF₅ crystallizes in the α-UF₅ structure type in the form of colorless needles. In comparison with the previously reported crystal-structure model [Hebecker (1971). Z. Anorg. Allg. Chem. 384, 111–114], the lattice parameters and fractional atomic coordinates were determined to much higher precision and all atoms were refined anisotropically, leading to a significantly improved structure model. The Bi atom (site symmetry 4/m..) is surrounded by six F atoms in a distorted octa­hedral coordination environment. The [BiF₆] octa­hedra are corner-linked to form infinite straight chains extending parallel to [001]. Density functional theory (DFT) calculations at the PBE0/TZVP level of theory were performed on the crystal structure of BiF₅ to calculate its IR and Raman spectra. These are compared with experimental data.

1. Chemical context

Bismuth(V) fluoride was first synthesized in the year 1940 (von Wartenberg et al., 1940). Hebecker first determined its crystal structure in 1971 (Hebecker, 1971). During our studies of the chemistry of BiF₅, we rerefined its crystal structure on basis of single-crystal data and recorded its IR and Raman spectra.

2. Structural commentary

Bismuth(V) fluoride crystallizes in the tetra­gonal space group I4/m, Pearson symbol tI12 and Wyckoff sequence 87.hba. BiF₅ adopts the α-UF₅ structure type and exhibits Bi—F bond lengths of 1.941 (4) (4×) and 2.1130 (5) Å (2×). The structure consists of chains of trans-corner-sharing [BiF₆] octa­hedra (point group symmetry 4/m..; Fig. 1) running parallel to the c axis. The chains can be described by the Niggli formula ¹_∞[BiF_4/1F_2/2]. The F1 atom bridges adjacent Bi atoms in the straight chain. As expected, the axial Bi—F1 bond lengths are longer than the four equatorial Bi—F2 bond lengths to the terminal ligands. Sections of the crystal structure showing the chains are shown in Fig. 2.

Figure 1 The coordination sphere of the Bi atom in the crystal structure of BiF5. Displacement ellipsoids are drawn at the 70% probability level. [Symmetry codes: (i) x, y, z  − 1; (ii) y, −x, z; (iii) −y, x, z; (iv) −x, −y, z.]

Figure 2 Crystal structure of BiF5 viewed along the b axis (left) and the c axis (right). The [BiF6] octa­hedra are shown in grey.

van der Waals contacts exist between neighbouring chains with inter­atomic distances of 2.944 (5) Å (F2⋯F2^v) and 2.952 (5) Å (F1⋯F2^v) [symmetry code: (v)  − x,  − y,  + z). Compared with the distances reported previously (Hebecker, 1971), these are 0.12 Å shorter for d(F2⋯F2) and 0.05 Å longer for d(F1⋯F2).

Regarding the crystal packing, a Bi atom is surrounded by 14 other Bi atoms in the shape of a distorted rhombic dodeca­hedron, which would correspond to the arrangement of the atoms in the W structure type. However, the rhombic dodeca­hedron is compressed due to the shorter intra­chain and the longer inter­chain Bi⋯Bi distances. The F1 atoms reside in the octa­hedral voids of the (idealized) body-centered cubic packing, while the F2 atoms are strongly displaced from these as the octa­hedra are rotated around the c axis (Fig. 2).

3. Vibrational spectra

IR and Raman spectra were recorded on a polycrystalline sample of BiF₅ at 293 K. Quantum-chemical calculations at the DFT-PBE0/TZVP level of theory (Dovesi et al., 2018; Zicovich-Wilson et al., 2004; Pascale et al., 2004; Maschio et al., 2013) were performed on basis of the crystal structure of BiF₅ to obtain the theoretical IR and Raman spectra. The recorded and calculated spectra are in good agreement, as shown in Figs. 3 and 4. A comparison of the observed and calculated bands is given in Table 1.

Table 1
Band positions (cm⁻¹) and band assignment of the IR and Raman spectra of solid BiF₅ based on the calculated spectrum

ν = stretching vibration, δ = bending vibration, s = symmetric, as = asymmetric, – = not observed.

IR		Raman		Assignment
νcalc	vobs	νcalc	vobs
630	618	–	–	vas(Bi—F2) + δ(Bi—F1—Bi)
–	–	607	596, 593	vs(Bi—F2)
–	–	578	571, 567	vas(Bi—F2)
453	441	–	–	vas(Bi—Fμ)
–	–	256	254	δ(F2—Bi—F2)
202	–	–	–	δ(F—Bi—F)
168	–	–	–	δ(F—Bi—F)
–	–	177	164	δ(F2—Bi—F1)
125	–	–	–	δ(F2—Bi—F1) + vas(Bi—F1)

Figure 3 Recorded IR spectrum of crystalline BiF5 in black and calculated IR absorbance spectrum of solid BiF5 at the DFT-PBE0/TZVP level of theory in red. No bands were observed in the region from 1000 to 4000 cm^−1.

Figure 4 Recorded Raman spectrum (532 nm laser) of crystalline BiF5 in black, calculated Raman spectrum of solid BiF5 at the DFT-PBE0/TZVP level of theory in red. No bands were observed in the region from 1000 to 4000 cm^−1.

4. Synthesis and crystallization

Bismuth(III) fluoride (1.05 g, 3.95 mmol) was loaded in a corundum boat and placed inside a tube furnace. By passing diluted fluorine (F₂/Ar, 10:90 v/v, Solvay) over the submitted material, bis­muth(V) fluoride was synthesized at 723 K, using a heating rate of 4 K min⁻¹ from room temperature to 723 K and a holding time of 10 h while diluted fluorine was passed with a flow rate of 5 standard cubic centimeters per minute. After cooling down to room temperature, colorless needles of bis­muth(V) fluoride (601 mg, 1.98 mmol, 57%) were isolated.

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2.

Table 2
Experimental details

Crystal data
Chemical formula	BiF5
Mr	303.98
Crystal system, space group	Tetragonal, I4/m
Temperature (K)	100
a, c (Å)	6.4439 (9), 4.2260 (9)
V (Å^3)	175.48 (6)
Z	2
Radiation type	Mo Kα
μ (mm^−1)	49.84
Crystal size (mm)	0.31 × 0.13 × 0.11
Data collection
Diffractometer	Stoe IPDS 2T
Absorption correction	Multi-scan (LANA; Koziskova et al., 2016)
Tmin, Tmax	0.006, 0.078
No. of measured, independent and observed [I > 2σ(I)] reflections	1134, 174, 174
Rint	0.027
(sin θ/λ)max (Å^−1)	0.742
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.016, 0.042, 1.12
No. of reflections	174
No. of parameters	12
Δρmax, Δρmin (e Å^−3)	0.90, −1.38
Computer programs: X-AREA (Stoe, 2020), SHELXT (Sheldrick, 2015a), SHELXL (Sheldrick, 2015b), DIAMOND (Brandenburg & Putz, 2022), publCIF (Westrip, 2010) and ShelXle (Hübschle et al., 2011).

Supporting information

Computing details

Bismuth pentafluoride

Crystal data

BiF5	Dx = 5.753 Mg m^−3
Mr = 303.98	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, I4/m	Cell parameters from 5333 reflections
a = 6.4439 (9) Å	θ = 8.8–60.0°
c = 4.2260 (9) Å	µ = 49.84 mm^−1
V = 175.48 (6) Å^3	T = 100 K
Z = 2	Needle, colorless
F(000) = 256	0.31 × 0.13 × 0.11 mm

Data collection

Stoe IPDS 2T diffractometer	174 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	174 reflections with I > 2σ(I)
Detector resolution: 6.67 pixels mm^-1	Rint = 0.027
rotation method, ω scans	θmax = 31.8°, θmin = 4.5°
Absorption correction: multi-scan (LANA; Koziskova et al., 2016)	h = −9→9
Tmin = 0.006, Tmax = 0.078	k = −9→9
1134 measured reflections	l = −5→6

Refinement

Refinement on F^2	Primary atom site location: dual
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0237P)^2 + 2.0256P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.016	(Δ/σ)max < 0.001
wR(F^2) = 0.042	Δρmax = 0.90 e Å^−3
S = 1.12	Δρmin = −1.38 e Å^−3
174 reflections	Extinction correction: SHELXL2018/3 (Sheldrick 2015b), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
12 parameters	Extinction coefficient: 0.0080 (17)
0 restraints

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Bi	0.000000	0.000000	0.000000	0.0199 (2)
F1	0.000000	0.000000	0.500000	0.0255 (15)
F2	0.2859 (7)	0.0950 (7)	0.000000	0.0275 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Bi	0.0225 (2)	0.0225 (2)	0.0147 (2)	0.000	0.000	0.000
F1	0.029 (2)	0.029 (2)	0.018 (3)	0.000	0.000	0.000
F2	0.0232 (17)	0.0320 (19)	0.0274 (19)	−0.0031 (14)	0.000	0.000

Geometric parameters (Å, º)

Bi—F2^i	1.941 (4)	Bi—F2	1.941 (4)
Bi—F2^ii	1.941 (4)	Bi—F1	2.1130 (5)
Bi—F2^iii	1.941 (4)	Bi—F1^iv	2.1130 (5)
F2^i—Bi—F2^ii	90.0	F2^iii—Bi—F1	90.0
F2^i—Bi—F2^iii	90.0	F2—Bi—F1	90.0
F2^ii—Bi—F2^iii	180.0 (3)	F2^i—Bi—F1^iv	90.0
F2^i—Bi—F2	180.0	F2^ii—Bi—F1^iv	90.0
F2^ii—Bi—F2	90.0	F2^iii—Bi—F1^iv	90.0
F2^iii—Bi—F2	90.0	F2—Bi—F1^iv	90.0
F2^i—Bi—F1	90.0	F1—Bi—F1^iv	180.0
F2^ii—Bi—F1	90.0	Bi^v—F1—Bi	180.0

Symmetry codes: (i) −x, −y, −z; (ii) y, −x, −z; (iii) −y, x, z; (iv) x, y, z−1; (v) x, y, z+1.

Fractional atomic coordinates and isotropic displacement parameters (Ų).

	x	y	z	Uiso
Bi	0	0	0	0.0199 (2)
F1	0	0	1/2	0.0255 (15)
F2	0.2859 (7)	0.0950 (7)	0	0.0275 (8)