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Strontium trioxoselenate(IV), SrSeO3, crystallizes in the KClO3 structure type and is isotypic with BaSeO3, β-PbSeO3 and the mineral scotlandite (PbSO3). The Sr2+ cation is nine-coordinated by O atoms. The SrO9 polyhedra are linked together by common edges to form a three-dimensional network, with channels running along the b axis where the Se4+ cations reside. They are coordinated by three O atoms to form one-sided SeO3E pyramids (E = electron lone pair), with Se—O bond lengths of 1.672 (6) and 1.688 (3) Å (× 2). The SeO3E pyramids are not connected to each other; instead, they share O atoms with the SrO9 polyhedra. Except for one O atom, all other atoms (one Sr, one Se and the second O atom) are located on mirror planes.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807025135/wm2114sup1.cif
Contains datablocks global, I

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S1600536807025135/wm2114Isup2.rtv
Contains datablock I

Key indicators

  • Powder neutron study
  • T = 295 K
  • Mean [sigma](e-O) = 0.004 Å
  • R factor = 0.000
  • wR factor = 0.000
  • Data-to-parameter ratio = 0.0

checkCIF/PLATON results

No syntax errors found



Alert level C REFI023_ALERT_1_C _refine_diff_density_max is missing Maximum value of final difference map (e A-3). The following tests will not be performed DIFMN_01,DIFMX_01,DIFMX_02 REFI024_ALERT_1_C _refine_diff_density_min is missing Minimum value of final difference map (e A-3). The following tests will not be performed DIFMN_01,DIFMN_02,DIFMN_03
Alert level G ABSMU_01 Radiation type not identified. Calculation of _exptl_absorpt_correction_mu not performed. PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints ....... 3
0 ALERT level A = In general: serious problem 0 ALERT level B = Potentially serious problem 2 ALERT level C = Check and explain 1 ALERT level G = General alerts; check 2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 0 ALERT type 2 Indicator that the structure model may be wrong or deficient 1 ALERT type 3 Indicator that the structure quality may be low 0 ALERT type 4 Improvement, methodology, query or suggestion 0 ALERT type 5 Informative message, check

Comment top

Multinary Te(IV) and Se(IV) oxides have been extensively studied in recent decades due to their potential non-linear optical and ferroelectric properties. The first tellurate(IV) where ferroelectric properties have been discovered is SrTeO3 (Yamada & Iwasaki, 1972). It is polymorphic and has a relatively complex crystal structure (Elerman, 1993; Dityatiev et al. 2006; Zavodnik et al., 2007), and no analogous structures have been reported so far. The alkaline earth homologues MTeO3 (M = Ca, Ba) adopt different structures (Kocak et al., 1979; Folger, 1975), and the crystal structure of the selenium homologue SrSeO3 has not been structurally characterized so far.

During the review process we were notified that more or less simultaneously with our study the crystal structure of SrSeO3 was determined independently from single-crystal X-ray data. The results of the single-crystal study and a comparative discussion of isotypic and related compounds under consideration of a stereochemical equivalence of ESeO3 groups and tetrahedral TO4 groups will be published soon (Wildner & Giester, 2007). In comparison with the somewhat more precise single-crystal data, the results of the present powder diffraction study are essentially the same.

In the SrSeO3 structure the Sr2+ cation is coordinated by seven nearest O atoms up to 2.694 (5) Å and two more distant O atoms at 3.022 (2) Å (Table 1), which results in a distorted monocapped square antiprism as coordination polyhedron. The SrO9 polyhedra are linked together by common edges to form a three-dimensional network with channels running along b, where the Se4+ atoms are located (Fig. 1a). They are coordinated by three O atoms forming SeO3E pyramids (E = electron lone pair; Fig. 1 b) with basal oxygen planes parallel to each other (Fig. 2). Each pyramid is linked to six SrO9 polyhedra, sharing O—O edges with three SrO9 polyhedra and oxygen vertices with another three Sr polyhedra (Fig. 1 b). The Se—O bonds are directed to opposite sides of the Sr–O network channels and act as additional links (Fig. 1a). The remaining "empty" volume of the channels accommodates the stereochemically active lone pairs of the Se4+ cations.

The structure of SrSeO3 is unrelated to that of the heavier homologue SrTeO3, but crystallizes in the KClO3 structure type (Danielsen et al., 1981) and is isotypic with BaSeO3 (Giester & Lengauer, 1998), β-PbSeO3 (Koskenlinna & Valkonen, 1977) and the mineral scotlandite (PbSO3) (Pertlik & Zemann, 1985). All the MXO3 (M = Pb, Ba; X = Se, S) compounds (Table 2) are built up of MO9 polyhedra forming the network, with channels occupied by the lone-pair cations X4+. The M—O bond lengths are shown in Fig. 3, which reflects the distortions of the corresponding polyhedra. For the selenates(IV), the M-O coordination may be considered as 7 (2.53– 2.87 Å) + 2 (3.02–3.04 Å). If the degree of deformation (Δ) is estimated as the difference between the longest and the shortest M—O bonds, for M = Ba and Sr Δ amounts to 0.392 and 0.326 Å, respectively, but for PbSeO3 Δ is much larger (0.511 Å). The discrepancy may be explained by the presence of Pb2+ with its additional electron lone pair. On the other hand, for scotlandite Δ is 0.304 Å which is even smaller than that estimated for related alkaline earth selenites.

Related literature top

For precipitation of SrSeO3 from aqueous solutions, see: Continéanu (1994); Fatu et al. (2003). The structure of SrSeO3 is unrelated to that of the polymorphic SrTeO3 (Yamada & Iwasaki, 1972; Elerman, 1993; Dityatiev et al., 2006; Zavodnik et al., 2007a,b), but crystallizes in the KClO3 structure type (Danielsen et al. 1981). It is isotypic with BaSeO3 (Giester & Lengauer, 1998), β-PbSeO3 (Koskenlinna & Valkonen, 1977) and PbSO3 (Pertlik & Zemann, 1985). The results of the present powder diffraction study are nearly the same as those of the independent single-crystal study of SrSeO3 (Wildner & Giester, 2007). For structures of the MTeO3 (M = Ca, Ba) homologues, see Kocak et al. (1979) and Folger (1975).

Experimental top

Hot aqueous solutions of Na2SeO3 and Sr(NO3)2 (both chemically pure) were mixed in the stoichiometric ratio 1:1 which resulted in slow precipitation of a fine white powder. The product with the best crystallinity was obtained by mixing the hot solutions (acidified to pH 1) and by subsequent slow neutralization with an aqueous solution of ammonia. The product was then repeatedly washed with hot water and decanted, and finally dried at 423–473 K.

The IR spectrum, recorded as a hexachlorobenzene suspension placed between two NaCl disks on a "Specord" spectrophotometer, showed no absorption bands in the 4000–2000 cm-1 region, thus ruling out incorporation of OH- or water. Thermal analysis performed on a Perkin-Elmer TG7 derivatograph in air up to 1323 K showed absence of any phase transitions, oxidation or decomposition reactions.

Our results disagree with those given by Continéanu (1994) and Fatu et al. (2003) who obtained SrSeO3.4.5H2O under similar conditions. It is most likely that strontium selenate(IV) crystallizes from aqueous solutions as SrSeO3.4.5H2O at room temperature, but as anhydrous SrSeO3 at about 373 K. Indeed, the sample precipitated at room temperature had a different X-ray pattern, however, with rather poor quality which prevented further X-ray studies.

Refinement top

The X-ray data for structure determination were collected on a Stoe Stadi/P transmission system, using monochromatic Cu Kα1 radiation, over the range of 5–120°/2θ with a step size of 0.02°. Satisfactory R values (R = 18%) were found when the atomic parameters of the heavy atoms of the isotypic BaSeO3 (Giester & Lengauer, 1998) were used as a starting model. However, we were not able to localize all oxygen atoms. Therefore we have supplemented our investigation with a neutron powder diffraction study which helped to refine the O atoms. The powder neutron diffraction data were collected on the high-flux powder diffractometer D2b at ILL, Grenoble. The SrSeO3 sample was loaded into a vanadium can, and data were collected at 295 K for about 2 h. In the final refinement cycles, all atoms were refined with isotropic temperature factors. The March–Dollase model (Dollase, 1986) showed the [010] direction for preferred orientation with a ratio of 0.88. The final Rietveld refinement plot (neutron data) for SrSeO3 is displayed in Fig. 4.

Structure description top

Multinary Te(IV) and Se(IV) oxides have been extensively studied in recent decades due to their potential non-linear optical and ferroelectric properties. The first tellurate(IV) where ferroelectric properties have been discovered is SrTeO3 (Yamada & Iwasaki, 1972). It is polymorphic and has a relatively complex crystal structure (Elerman, 1993; Dityatiev et al. 2006; Zavodnik et al., 2007), and no analogous structures have been reported so far. The alkaline earth homologues MTeO3 (M = Ca, Ba) adopt different structures (Kocak et al., 1979; Folger, 1975), and the crystal structure of the selenium homologue SrSeO3 has not been structurally characterized so far.

During the review process we were notified that more or less simultaneously with our study the crystal structure of SrSeO3 was determined independently from single-crystal X-ray data. The results of the single-crystal study and a comparative discussion of isotypic and related compounds under consideration of a stereochemical equivalence of ESeO3 groups and tetrahedral TO4 groups will be published soon (Wildner & Giester, 2007). In comparison with the somewhat more precise single-crystal data, the results of the present powder diffraction study are essentially the same.

In the SrSeO3 structure the Sr2+ cation is coordinated by seven nearest O atoms up to 2.694 (5) Å and two more distant O atoms at 3.022 (2) Å (Table 1), which results in a distorted monocapped square antiprism as coordination polyhedron. The SrO9 polyhedra are linked together by common edges to form a three-dimensional network with channels running along b, where the Se4+ atoms are located (Fig. 1a). They are coordinated by three O atoms forming SeO3E pyramids (E = electron lone pair; Fig. 1 b) with basal oxygen planes parallel to each other (Fig. 2). Each pyramid is linked to six SrO9 polyhedra, sharing O—O edges with three SrO9 polyhedra and oxygen vertices with another three Sr polyhedra (Fig. 1 b). The Se—O bonds are directed to opposite sides of the Sr–O network channels and act as additional links (Fig. 1a). The remaining "empty" volume of the channels accommodates the stereochemically active lone pairs of the Se4+ cations.

The structure of SrSeO3 is unrelated to that of the heavier homologue SrTeO3, but crystallizes in the KClO3 structure type (Danielsen et al., 1981) and is isotypic with BaSeO3 (Giester & Lengauer, 1998), β-PbSeO3 (Koskenlinna & Valkonen, 1977) and the mineral scotlandite (PbSO3) (Pertlik & Zemann, 1985). All the MXO3 (M = Pb, Ba; X = Se, S) compounds (Table 2) are built up of MO9 polyhedra forming the network, with channels occupied by the lone-pair cations X4+. The M—O bond lengths are shown in Fig. 3, which reflects the distortions of the corresponding polyhedra. For the selenates(IV), the M-O coordination may be considered as 7 (2.53– 2.87 Å) + 2 (3.02–3.04 Å). If the degree of deformation (Δ) is estimated as the difference between the longest and the shortest M—O bonds, for M = Ba and Sr Δ amounts to 0.392 and 0.326 Å, respectively, but for PbSeO3 Δ is much larger (0.511 Å). The discrepancy may be explained by the presence of Pb2+ with its additional electron lone pair. On the other hand, for scotlandite Δ is 0.304 Å which is even smaller than that estimated for related alkaline earth selenites.

For precipitation of SrSeO3 from aqueous solutions, see: Continéanu (1994); Fatu et al. (2003). The structure of SrSeO3 is unrelated to that of the polymorphic SrTeO3 (Yamada & Iwasaki, 1972; Elerman, 1993; Dityatiev et al., 2006; Zavodnik et al., 2007a,b), but crystallizes in the KClO3 structure type (Danielsen et al. 1981). It is isotypic with BaSeO3 (Giester & Lengauer, 1998), β-PbSeO3 (Koskenlinna & Valkonen, 1977) and PbSO3 (Pertlik & Zemann, 1985). The results of the present powder diffraction study are nearly the same as those of the independent single-crystal study of SrSeO3 (Wildner & Giester, 2007). For structures of the MTeO3 (M = Ca, Ba) homologues, see Kocak et al. (1979) and Folger (1975).

Computing details top

Data collection: local program at ILL; cell refinement: GSAS (Larson & Von Dreele, 1987); data reduction: local program at ILL; program(s) used to solve structure: coordinates taken from an isotypic compound (Giester & Lengauer, 1998); program(s) used to refine structure: GSAS; molecular graphics: DIAMOND (Brandenburg, 2001); software used to prepare material for publication: GSAS.

Figures top
[Figure 1] Fig. 1. The crystal structure of SrSeO3: a) The network of SrO9 polyhedra with the Se atoms located in the channels; b) The SeO3E pyramid linked to the SrO9 polyhedra.
[Figure 2] Fig. 2. Arrangement of the oxygen basal planes of the SeO3 groups in SrSeO3.
[Figure 3] Fig. 3. The M—O distances in isotypic MXO3 (M = Sr, Ba, Pb; X =Se, S) compounds.
[Figure 4] Fig. 4. Final Rietveld refinement plot for SrSeO3 from neutron data.
Strontium trioxoselenate(IV) top
Crystal data top
SrSeO3Z = 2
Mr = 214.58Dx = 4.661 Mg m3
Monoclinic, P21/mNeutron radiation, λ = 1.59432 Å
Hall symbol: -P 2ybµ = 0.02 mm1
a = 6.5702 (4) ÅT = 295 K
b = 5.4749 (3) ÅParticle morphology: irregular
c = 4.4550 (3) Åwhite
β = 107.419 (4)°cylinder, 30 × 10 mm
V = 152.90 (2) Å3Specimen preparation: Prepared at 473 K and ambient kPa
Data collection top
D2b at ILL
diffractometer
Data collection mode: transmission
Radiation source: reactorScan method: step
Specimen mounting: vanadium can
Refinement top
Least-squares matrix: fullProfile function: CW Profile function number 2 with 18 terms Profile coefficients for Simpson's rule integration of pseudovoigt function (Howard, 1982; Thompson et al., 1987). #1(GU) = 89.779 #2(GV) = -57.381 #3(GW) = 105.091 #4(LX) = 20.389 #5(LY) = 0.000 #6(trns) = 0.000 #7(asym) = 12.8654 #8(shft) = 0.0000 #9(GP) = 0.000 #10(stec)= 0.00 #11(ptec)= 0.00 #12(sfec)= 0.00 #13(L11) = 0.000 #14(L22) = 0.000 #15(L33) = 0.000 #16(L12) = 0.000 #17(L13) = 0.000 #18(L23) = 0.000 Peak tails are ignored where the intensity is below 0.0005 times the peak Aniso. broadening axis 0.0 0.0 1.0
Rp = 0.06434 parameters
Rwp = 0.0823 restraints
Rexp = 0.128(Δ/σ)max = 0.03
R(F2) = 0.09304Background function: GSAS Background function number 2 with 9 terms. Cosine Fourier series 1: 41.2702 2: -6.01889 3: 7.41766 4: -0.953855 5: 5.20570 6: -0.565862 7: 2.33917 8: 5.496910E-02 9: 1.77775
Excluded region(s): nonePreferred orientation correction: March–Dollase (Dollase, 1986) AXIS 1 Ratio = 0.88823 h = 0.000 k = 1.000 l = 0.000 Prefered orientation correction range: Min = 0.83687, Max = 1.42785
Crystal data top
SrSeO3V = 152.90 (2) Å3
Mr = 214.58Z = 2
Monoclinic, P21/mNeutron radiation, λ = 1.59432 Å
a = 6.5702 (4) ŵ = 0.02 mm1
b = 5.4749 (3) ÅT = 295 K
c = 4.4550 (3) Åcylinder, 30 × 10 mm
β = 107.419 (4)°
Data collection top
D2b at ILL
diffractometer
Data collection mode: transmission
Specimen mounting: vanadium canScan method: step
Refinement top
Rp = 0.064R(F2) = 0.09304
Rwp = 0.08234 parameters
Rexp = 0.1283 restraints
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Sr10.7016 (5)0.250.3473 (9)0.0070 (8)*
Se10.1566 (5)0.250.0639 (8)0.0104 (7)*
O10.1081 (8)0.250.6735 (11)0.0220 (12)*
O20.3287 (4)0.4855 (4)0.1743 (8)0.0078 (6)*
Geometric parameters (Å, º) top
Sr1—O1i2.631 (6)Sr1—O2v2.694 (5)
Sr1—O1ii3.022 (3)Sr1—O2vi2.633 (4)
Sr1—O1iii3.022 (3)Sr1—O2vii2.670 (4)
Sr1—O22.670 (4)Se1—O1viii1.672 (6)
Sr1—O2iv2.694 (5)Se1—O21.688 (3)
Sr1—O2ii2.633 (4)Se1—O2vii1.688 (3)
O1ii—Sr1—O1iii129.8 (2)O2ii—Sr1—O2vi66.72 (16)
O1ii—Sr1—O2141.34 (14)O2ii—Sr1—O2ix71.51 (13)
O1ii—Sr1—O2iv53.94 (11)O2v—Sr1—O2vi113.49 (8)
O1ii—Sr1—O2ii70.05 (11)O2v—Sr1—O2ix100.73 (13)
O1ii—Sr1—O2v112.64 (14)O2vi—Sr1—O2ix102.35 (12)
O1ii—Sr1—O2vi130.92 (16)Sr1—Se1—O1viii103.7 (2)
O1ii—Sr1—O2ix84.61 (11)Sr1—Se1—O249.98 (13)
O1iii—Sr1—O284.61 (11)Sr1—Se1—O2ix49.98 (13)
O1iii—Sr1—O2iv112.64 (14)O1viii—Se1—O2101.88 (19)
O1iii—Sr1—O2ii130.92 (16)O1viii—Se1—O2ix101.88 (19)
O1iii—Sr1—O2v53.94 (11)O2—Se1—O2ix99.6 (3)
O1iii—Sr1—O2vi70.05 (11)Sr1x—O1—Sr1ii110.12 (11)
O1iii—Sr1—O2ix141.34 (14)Sr1x—O1—Sr1iii110.12 (11)
O2—Sr1—O2iv100.73 (13)Sr1x—O1—Se1xi114.9 (3)
O2—Sr1—O2ii102.35 (12)Sr1ii—O1—Sr1iii129.8 (2)
O2—Sr1—O2v70.55 (11)Sr1ii—O1—Se1xi94.58 (14)
O2—Sr1—O2vi71.51 (13)Sr1iii—O1—Se1xi94.58 (14)
O2—Sr1—O2ix57.75 (12)Sr1—O2—Sr1xii109.45 (11)
O2iv—Sr1—O2ii113.49 (8)Sr1—O2—Sr1iii108.49 (13)
O2iv—Sr1—O2v65.02 (13)Sr1—O2—Se1101.06 (15)
O2iv—Sr1—O2vi171.8 (2)Sr1xii—O2—Sr1iii113.49 (8)
O2iv—Sr1—O2ix70.55 (11)Sr1xii—O2—Se1106.80 (19)
O2ii—Sr1—O2v171.8 (2)Sr1iii—O2—Se1116.72 (17)
Symmetry codes: (i) x+1, y, z; (ii) x+1, y1/2, z+1; (iii) x+1, y+1/2, z+1; (iv) x+1, y1/2, z; (v) x+1, y+1, z; (vi) x+1, y+1, z+1; (vii) x, y+1/2, z; (viii) x, y, z1; (ix) x, y+3/2, z; (x) x1, y, z; (xi) x, y, z+1; (xii) x+1, y+1/2, z.

Experimental details

Crystal data
Chemical formulaSrSeO3
Mr214.58
Crystal system, space groupMonoclinic, P21/m
Temperature (K)295
a, b, c (Å)6.5702 (4), 5.4749 (3), 4.4550 (3)
β (°) 107.419 (4)
V3)152.90 (2)
Z2
Radiation typeNeutron, λ = 1.59432 Å
µ (mm1)0.02
Specimen shape, size (mm)Cylinder, 30 × 10
Data collection
DiffractometerD2b at ILL
Specimen mountingVanadium can
Data collection modeTransmission
Scan methodStep
2θ values (°)2θmin = ? 2θmax = ? 2θstep = ?
Refinement
R factors and goodness of fitRp = 0.064, Rwp = 0.082, Rexp = 0.128, R(F2) = 0.09304, χ2 = 0.423
No. of parameters34
No. of restraints3

Computer programs: local program at ILL, GSAS (Larson & Von Dreele, 1987), coordinates taken from an isotypic compound (Giester & Lengauer, 1998), GSAS, DIAMOND (Brandenburg, 2001).

Selected geometric parameters (Å, º) top
Sr1—O1i2.631 (6)Sr1—O2v2.694 (5)
Sr1—O1ii3.022 (3)Sr1—O2vi2.633 (4)
Sr1—O1iii3.022 (3)Sr1—O2vii2.670 (4)
Sr1—O22.670 (4)Se1—O1viii1.672 (6)
Sr1—O2iv2.694 (5)Se1—O21.688 (3)
Sr1—O2ii2.633 (4)Se1—O2vii1.688 (3)
O1viii—Se1—O2101.88 (19)O2—Se1—O2ix99.6 (3)
O1viii—Se1—O2ix101.88 (19)
Symmetry codes: (i) x+1, y, z; (ii) x+1, y1/2, z+1; (iii) x+1, y+1/2, z+1; (iv) x+1, y1/2, z; (v) x+1, y+1, z; (vi) x+1, y+1, z+1; (vii) x, y+1/2, z; (viii) x, y, z1; (ix) x, y+3/2, z.
The unit-cell parameters for isotypic MXO3 compounds (M = Ba or Pb; X = S or Se) and the lengths of the Se(S)—O bonds (Å, °) top
CompoundabcβSe(S)—O
BaSeO3a4.6775.6456.851107.161.690, 1.693 (× 2)
β-PbSeO3b4.57375.51376.634106.5471.674, 1.729 (× 2)
Scotlanditec4.5055.3336.405106.241.507, 1.529 (× 2)
Notes: (a) Giester & Lengauer (1998); (b) Koskenlinna & Valkonen (1977); (c) Pertlik & Zemann (1985).
 

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