Acta Cryst. (2007). E63, i149-i150 [ doi:10.1107/S1600536807025135 ]
Strontium trioxoselenate(IV), SrSeO3, crystallizes in the KClO3 structure type and is isotypic with BaSeO3, ![[beta]](/logos/entities/beta_rmgif.gif)
-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.
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.
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.
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.
![[Figure 1]](./wm2114fig1thm.gif)
| 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]](./wm2114fig2thm.gif)
| Fig. 2. Arrangement of the oxygen basal planes of the SeO3 groups in SrSeO3. |
![[Figure 3]](./wm2114fig3thm.gif)
| Fig. 3. The M—O distances in isotypic MXO3 (M = Sr, Ba, Pb; X =Se, S) compounds. |
![[Figure 4]](./wm2114fig4thm.gif)
| Fig. 4. Final Rietveld refinement plot for SrSeO3 from neutron data. |
| SrSeO3 | Z = 2 |
| Mr = 214.58 | Dx = 4.661 Mg m−3 |
| Monoclinic, P21/m | Neutron radiation, λ = 1.59432 Å |
| Hall symbol: -P 2yb | µ = 0.02 mm−1 |
| a = 6.5702 (4) Å | T = 295 K |
| b = 5.4749 (3) Å | Particle morphology: irregular |
| c = 4.4550 (3) Å | white |
| β = 107.419 (4)° | cylinder, 30 × 10 mm |
| V = 152.90 (2) Å3 | Specimen preparation: Prepared at 473 K and ambient kPa |
| D2b at ILL diffractometer | Data collection mode: transmission |
| Radiation source: reactor | Scan method: step |
| Specimen mounting: vanadium can |
| Least-squares matrix: full | Excluded region(s): none |
| Rp = 0.064 | Profile 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 |
| Rwp = 0.082 | 34 parameters |
| Rexp = 0.128 | 3 restraints |
| R(F2) = 0.09304 | (Δ/σ)max = 0.03 |
| χ2 = 0.423 | Background 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 |
| ? data points | Preferred 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 |
| SrSeO3 | V = 152.90 (2) Å3 |
| Mr = 214.58 | Z = 2 |
| Monoclinic, P21/m | Neutron radiation, λ = 1.59432 Å |
| a = 6.5702 (4) Å | µ = 0.02 mm−1 |
| b = 5.4749 (3) Å | T = 295 K |
| c = 4.4550 (3) Å | cylinder, 30 × 10 mm |
| β = 107.419 (4)° |
| D2b at ILL diffractometer | Scan method: step |
| Specimen mounting: vanadium can | 2θmin = ?°, 2θmax = ?°, 2θstep = ?° |
| Data collection mode: transmission |
| Rp = 0.064 | R(F2) = 0.09304 |
| Rwp = 0.082 | χ2 = 0.423 |
| Rexp = 0.128 | ? data points |
| RBragg = ? | 34 parameters |
| R(F) = ? | 3 restraints |
| x | y | z | Uiso*/Ueq | ||
| Sr1 | 0.7016 (5) | 0.25 | 0.3473 (9) | 0.0070 (8)* | |
| Se1 | 0.1566 (5) | 0.25 | 0.0639 (8) | 0.0104 (7)* | |
| O1 | 0.1081 (8) | 0.25 | 0.6735 (11) | 0.0220 (12)* | |
| O2 | 0.3287 (4) | 0.4855 (4) | 0.1743 (8) | 0.0078 (6)* |
| Sr1—O1i | 2.631 (6) | Sr1—O2v | 2.694 (5) |
| Sr1—O1ii | 3.022 (3) | Sr1—O2vi | 2.633 (4) |
| Sr1—O1iii | 3.022 (3) | Sr1—O2vii | 2.670 (4) |
| Sr1—O2 | 2.670 (4) | Se1—O1viii | 1.672 (6) |
| Sr1—O2iv | 2.694 (5) | Se1—O2 | 1.688 (3) |
| Sr1—O2ii | 2.633 (4) | Se1—O2vii | 1.688 (3) |
| O1ii—Sr1—O1iii | 129.8 (2) | O2ii—Sr1—O2vi | 66.72 (16) |
| O1ii—Sr1—O2 | 141.34 (14) | O2ii—Sr1—O2ix | 71.51 (13) |
| O1ii—Sr1—O2iv | 53.94 (11) | O2v—Sr1—O2vi | 113.49 (8) |
| O1ii—Sr1—O2ii | 70.05 (11) | O2v—Sr1—O2ix | 100.73 (13) |
| O1ii—Sr1—O2v | 112.64 (14) | O2vi—Sr1—O2ix | 102.35 (12) |
| O1ii—Sr1—O2vi | 130.92 (16) | Sr1—Se1—O1viii | 103.7 (2) |
| O1ii—Sr1—O2ix | 84.61 (11) | Sr1—Se1—O2 | 49.98 (13) |
| O1iii—Sr1—O2 | 84.61 (11) | Sr1—Se1—O2ix | 49.98 (13) |
| O1iii—Sr1—O2iv | 112.64 (14) | O1viii—Se1—O2 | 101.88 (19) |
| O1iii—Sr1—O2ii | 130.92 (16) | O1viii—Se1—O2ix | 101.88 (19) |
| O1iii—Sr1—O2v | 53.94 (11) | O2—Se1—O2ix | 99.61 (26) |
| O1iii—Sr1—O2vi | 70.05 (11) | Sr1x—O1—Sr1ii | 110.12 (11) |
| O1iii—Sr1—O2ix | 141.34 (14) | Sr1x—O1—Sr1iii | 110.12 (11) |
| O2—Sr1—O2iv | 100.73 (13) | Sr1x—O1—Se1xi | 114.9 (3) |
| O2—Sr1—O2ii | 102.35 (12) | Sr1ii—O1—Sr1iii | 129.8 (2) |
| O2—Sr1—O2v | 70.55 (11) | Sr1ii—O1—Se1xi | 94.58 (14) |
| O2—Sr1—O2vi | 71.51 (13) | Sr1iii—O1—Se1xi | 94.58 (14) |
| O2—Sr1—O2ix | 57.75 (12) | Sr1—O2—Sr1xii | 109.45 (11) |
| O2iv—Sr1—O2ii | 113.49 (8) | Sr1—O2—Sr1iii | 108.49 (13) |
| O2iv—Sr1—O2v | 65.02 (13) | Sr1—O2—Se1 | 101.06 (15) |
| O2iv—Sr1—O2vi | 171.8 (2) | Sr1xii—O2—Sr1iii | 113.49 (8) |
| O2iv—Sr1—O2ix | 70.55 (11) | Sr1xii—O2—Se1 | 106.80 (19) |
| O2ii—Sr1—O2v | 171.8 (2) | Sr1iii—O2—Se1 | 116.72 (17) |
| Symmetry codes: (i) x+1, y, z; (ii) −x+1, y−1/2, −z+1; (iii) −x+1, y+1/2, −z+1; (iv) −x+1, y−1/2, −z; (v) −x+1, −y+1, −z; (vi) −x+1, −y+1, −z+1; (vii) x, −y+1/2, z; (viii) x, y, z−1; (ix) x, −y+3/2, z; (x) x−1, y, z; (xi) x, y, z+1; (xii) −x+1, y+1/2, −z. |
| Sr1—O1i | 2.631 (6) | Sr1—O2v | 2.694 (5) |
| Sr1—O1ii | 3.022 (3) | Sr1—O2vi | 2.633 (4) |
| Sr1—O1iii | 3.022 (3) | Sr1—O2vii | 2.670 (4) |
| Sr1—O2 | 2.670 (4) | Se1—O1viii | 1.672 (6) |
| Sr1—O2iv | 2.694 (5) | Se1—O2 | 1.688 (3) |
| Sr1—O2ii | 2.633 (4) | Se1—O2vii | 1.688 (3) |
| O1viii—Se1—O2 | 101.88 (19) | O2—Se1—O2ix | 99.61 (26) |
| O1viii—Se1—O2ix | 101.88 (19) |
| Symmetry codes: (i) x+1, y, z; (ii) −x+1, y−1/2, −z+1; (iii) −x+1, y+1/2, −z+1; (iv) −x+1, y−1/2, −z; (v) −x+1, −y+1, −z; (vi) −x+1, −y+1, −z+1; (vii) x, −y+1/2, z; (viii) x, y, z−1; (ix) x, −y+3/2, z. |
| Compound | a | b | c | β | Se(S)—O |
| BaSeO3a | 4.677 | 5.645 | 6.851 | 107.16 | 1.690, 1.693 (× 2) |
| β-PbSeO3b | 4.5737 | 5.5137 | 6.634 | 106.547 | 1.674, 1.729 (× 2) |
| Scotlanditec | 4.505 | 5.333 | 6.405 | 106.24 | 1.507, 1.529 (× 2) |
| Notes: (a) Giester & Lengauer (1998); (b) Koskenlinna & Valkonen (1977); (c) Pertlik & Zemann (1985). |
This work was carried out under partial funding of the Russian Foundation for Basic Research (grant Nos. RFFI 05–03–32719 and 06–03–32134). PSB thanks INTAS YSF for support (grant No. 05–109–4474).
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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.