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BiSeI crystals obtained by a chemical-transport reaction are orthorhombic (space group Pnma) with a = 8.6967 (17) Å, b = 4.2205 (8) Å and c = 10.574 (2) Å. It could be confimed that BiSeI crystallizes in the centrosymmetric SbSI structure type.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270199016017/qb0155sup1.cif
Contains datablocks bisei, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270199016017/qb0155Isup2.hkl
Contains datablock I

Comment top

The chalcogenide halides of antimony and bismuth have been known for a long time. Dönges studied crystals of the thiohalides (Dönges, 1950a) and selenohalides (Dönges, 1950b), and found that SbSBr, SbSI, BiSCl, BiSBr, BiSI, BiSeBr and BiSeI all crystallize in the same structure type. He was able to solve the structure of SbSI and determined the lattice spacings of the remaining members of that family.

After it was discovered that SbSI is both a photoconductor (Nitsche & Merz, 1960) and, at temperatures below 295 K, a ferroelectric (Fatuzzo et al., 1962), these compounds have been studied in great detail (for a review see, for example, Fenner et al., 1980). It is somewhat surprising that there are no single-crystal structure determinations that prove that SbSeBr, BiSeBr and BiSeI actually adopt the SbSI structure type. Since the other members of that series show some variablity in the exact positions of the atoms, it is worthwhile verifying that these phases are indeed isostructural.

According to our findings this is the case for bismuth selenide iodide.

Experimental top

A mixture of Bi, Se, P and I was sealed in an evacuated quartz ampoule and heated in a box furnace. The temperature was slowly raised to a nominal temperature of 600°C and kept constant for one week. The sample was then cooled within one day and black needle-like crystals could be collected from the top of the quartz ampoule. Since it has been shown that BiSeI melts incongruently at about 535°C (Belotskii et al., 1970), we suppose that the actual temperature at the top of the ampoule did not exceed that value. The crystals grown by this chemical-transport reaction were suitable for a single-crystal X-ray structure determination.

Refinement top

Several single crystals were broken off the quartz wall of the reaction container. The crystal quality was determined by collecting rotation frames on a Bruker CCD system. A suitable crystal with indexable faces was chosen for the data collection. An initial matrix was determined from 28 reflections from an initial measurement to compare the cell constants with previously published data (Fenner et al., 1980).

A full hemisphere was collected and the data have been integrated with a refined cell, assuming orthorhombic symmetry. Application of a numerical absorption correction [face indexing: Gaussian integration method (Busing & Levy, 1957), optimized by Sheldrick, 1998] resulted in a substantial improvement of Rint from 0.193 for the raw data to 0.0734 for the corrected data set.

The two space groups Pnma (centrosymmetric) and Pna21 (non-centrosymmetric) were consistent with the observed systematic absences. The refinement is possible in both space groups, leading to R values that were larger (by 0.032 for wR2) in the non-centrosymmetric case. The difference electron density was also slightly higher than for the refinement in Pnma. Most importantly, only one `free' positional parameter in Pna21 deviated by more than 3σ from the fixed value for the centrosymmetric case (considering the unconventional setting and the necessary origin shift).

Deepest hole −2.90 e Å−3 at (0.8122, 0.0463, 0.3720) (1.00 Å from Bi1); highest peak 2.31 e Å−3 at (0.6587, 1/4, 0.6864) (1.52 Å from I1).

Computing details top

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SHELXTL (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); software used to prepare material for publication: SHELXTL.

Bismuth Selenide Iodide top
Crystal data top
BiSeIDx = 7.100 Mg m3
Mr = 414.84Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, PnmaCell parameters from 443 reflections
a = 8.6967 (17) Åθ = 3.0–27.4°
b = 4.2205 (8) ŵ = 62.50 mm1
c = 10.574 (2) ÅT = 293 K
V = 388.11 (13) Å3Needle, metallic silver
Z = 40.22 × 0.03 × 0.02 mm
F(000) = 680
Data collection top
CCD area-detector
diffractometer
457 independent reflections
Radiation source: fine-focus sealed tube443 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.073
ω scanθmax = 27.4°, θmin = 3.0°
Absorption correction: integration
(Busing & Levy, 1957; Sheldrick, 1998)
h = 411
Tmin = 0.063, Tmax = 0.299k = 54
3812 measured reflectionsl = 1213
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.047 w = 1/[σ2(Fo2) + (0.0558P)2 + 36.994P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.123(Δ/σ)max < 0.001
S = 1.20Δρmax = 2.31 e Å3
457 reflectionsΔρmin = 2.90 e Å3
20 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0048 (8)
Crystal data top
BiSeIV = 388.11 (13) Å3
Mr = 414.84Z = 4
Orthorhombic, PnmaMo Kα radiation
a = 8.6967 (17) ŵ = 62.50 mm1
b = 4.2205 (8) ÅT = 293 K
c = 10.574 (2) Å0.22 × 0.03 × 0.02 mm
Data collection top
CCD area-detector
diffractometer
457 independent reflections
Absorption correction: integration
(Busing & Levy, 1957; Sheldrick, 1998)
443 reflections with I > 2σ(I)
Tmin = 0.063, Tmax = 0.299Rint = 0.073
3812 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0470 restraints
wR(F2) = 0.123 w = 1/[σ2(Fo2) + (0.0558P)2 + 36.994P]
where P = (Fo2 + 2Fc2)/3
S = 1.20Δρmax = 2.31 e Å3
457 reflectionsΔρmin = 2.90 e Å3
20 parameters
Special details top

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

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Bi10.87147 (11)0.25000.37255 (9)0.0192 (4)
I10.01489 (19)0.25000.17185 (15)0.0196 (5)
Se10.1694 (3)0.25000.4485 (2)0.0156 (6)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Bi10.0201 (6)0.0148 (6)0.0226 (6)0.0000.0033 (3)0.000
I10.0223 (9)0.0146 (8)0.0217 (9)0.0000.0033 (6)0.000
Se10.0152 (11)0.0116 (12)0.0201 (12)0.0000.0003 (9)0.000
Geometric parameters (Å, º) top
Bi1—Se1i2.713 (3)I1—Bi1v3.2423 (15)
Bi1—Se1ii2.8563 (18)I1—Bi1vi3.2423 (15)
Bi1—Se1iii2.8563 (18)Se1—Bi1v2.713 (3)
Bi1—I1i3.2423 (15)Se1—Bi1ii2.8563 (18)
Bi1—I1iv3.2423 (15)Se1—Bi1iii2.8563 (18)
Se1i—Bi1—Se1ii85.57 (6)Se1ii—Bi1—I1iv90.03 (4)
Se1i—Bi1—Se1iii85.57 (6)Se1iii—Bi1—I1iv164.20 (6)
Se1ii—Bi1—Se1iii95.26 (8)I1i—Bi1—I1iv81.21 (5)
Se1i—Bi1—I1i80.01 (5)Bi1v—I1—Bi1vi81.21 (5)
Se1ii—Bi1—I1i164.20 (6)Bi1v—Se1—Bi1ii94.44 (6)
Se1iii—Bi1—I1i90.03 (4)Bi1v—Se1—Bi1iii94.44 (6)
Se1i—Bi1—I1iv80.01 (5)Bi1ii—Se1—Bi1iii95.26 (8)
Symmetry codes: (i) x+1, y, z; (ii) x+1, y+1, z+1; (iii) x+1, y, z+1; (iv) x+1, y+1, z; (v) x1, y, z; (vi) x1, y1, z.

Experimental details

Crystal data
Chemical formulaBiSeI
Mr414.84
Crystal system, space groupOrthorhombic, Pnma
Temperature (K)293
a, b, c (Å)8.6967 (17), 4.2205 (8), 10.574 (2)
V3)388.11 (13)
Z4
Radiation typeMo Kα
µ (mm1)62.50
Crystal size (mm)0.22 × 0.03 × 0.02
Data collection
DiffractometerCCD area-detector
diffractometer
Absorption correctionIntegration
(Busing & Levy, 1957; Sheldrick, 1998)
Tmin, Tmax0.063, 0.299
No. of measured, independent and
observed [I > 2σ(I)] reflections
3812, 457, 443
Rint0.073
(sin θ/λ)max1)0.648
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.047, 0.123, 1.20
No. of reflections457
No. of parameters20
w = 1/[σ2(Fo2) + (0.0558P)2 + 36.994P]
where P = (Fo2 + 2Fc2)/3
Δρmax, Δρmin (e Å3)2.31, 2.90

Computer programs: SMART (Bruker, 1997), SMART, SHELXTL (Bruker, 1998), SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), SHELXTL.

 

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