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We present the structure of anhydrous sodium carbonate at room temperature (phase γ) and 110 K (phase δ) based on single-crystal X-ray diffraction data. The incommensurate phase γ was determined almost 30 years ago in the harmonic approximation using one modulation wave and first-order satellites. In our work we use satellites up to fifth order and additional harmonic waves to model the anharmonic features of the structure. The commensurate phase δ is presented for the first time. Using the superspace approach, both phases are compared in order to find common trends in the whole range of the sodium carbonate phases. We present arguments supporting the hypothesis that the driving force of the phase transitions may originate in the unsaturated bonding potential of one of the Na ions.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768103009017/sn0033sup1.cif
Contains datablocks global, I, II

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108768103009017/sn0033Isup2.hkl
Contains datablock I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108768103009017/sn0033IIsup3.hkl
Contains datablock II

Computing details top

For both compounds, data collection: (CCD, Kuma Diffraction, 1998); cell refinement: (RED v.168, Oxford Diffraction, 2001); data reduction: (RED v.168, Oxford Diffraction, 2001); program(s) used to solve structure: (Jana2000, Petricek and Dusek, 2000); program(s) used to refine structure: (Jana2000, Petricek and Dusek, 2000); molecular graphics: (Diamond 2.1c, Brandenburg, 1999) (Pictur, Dusek, 1994); software used to prepare material for publication: (Jana2000; Petricek and Dusek, 2000).

(I) sodium carbonate top
Crystal data top
Na2CO3F(000) = 208
Mr = 106Dx = 2.574 Mg m3
Monoclinic, C2/m(αlpha0γamma)0sMelting point: 851 C K
q = 0.16667a* + 0.33333c*Mo Kα radiation, λ = 0.71069 Å
a = 8.898 (7) ÅCell parameters from 1280 reflections
b = 5.237 (5) Åθ = 10–43°
c = 5.996 (5) ŵ = 0.50 mm1
β = 101.87 (8)°T = 110K K
V = 273.4 (8) Å3Potato, white
Z = 40.5mm × 0.45mm × 0.4mm mm
† Symmetry operations: (1) x1, x2, x3, x4; (2) −x1, x2, −x3, 1/2−x4; (3) −x1, −x2, −x3, −x4; (4) x1, −x2, x3, 1/2+x4; (5) 1/2+x1, 1/2+x2, x3, x4; (6) 1/2−x1, 1/2+x2, −x3, 1/2−x4; (7) 1/2−x1, 1/2−x2, −x3, −x4; (8) 1/2+x1, 1/2−x2, x3, 1/2+x4.

Data collection top
Xcalibur
diffractometer
No. of measured, independent and observed reflections: 61103, 12347, 5695 [I > 3σ(I)]; 2163, 2163, 1090 (Main); 3894, 3894, 1901 (Sat1); 4347, 4347, 1869 (Sat2); 1942, 1942, 837 (Sat3)
Radiation source: X-ray tubeRint = 0.067, 0.056 (Main), 0.066 (Sat1), 0.116 (Sat2), 0.156 (Sat3)
Graphite monochromatorθmax = 45.7°, θmin = 4.1°
Detector resolution: 8 pixels mm-1h = 1818
ο–scansk = 1010
Wave-vector determination: commensurate structurel = 1211
Refinement top
Refinement on F205 parameters
R[F2 > 2σ(F2)] = 0.045Weighting scheme based on measured s.u.'s w = 1/(σ2(F) + 0.0004F2)
wR(F2) = 0.066(Δ/σ)max = 0.003
S = 1.31Δρmax = 0.69 e Å3
5695 reflectionsΔρmin = 0.64 e Å3
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Na10000.00886 (10)
Na2000.50.00855 (10)
Na30.17125 (4)0.50.74784 (6)0.01267 (8)
C0.16454 (7)0.50.24887 (10)0.00695 (12)
O10.10175 (5)0.29345 (6)0.28667 (7)0.01312 (9)
O20.28941 (6)0.50.17472 (9)0.01135 (11)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Na10.00927 (18)0.00910 (12)0.00885 (17)00.00338 (15)0
Na20.01018 (18)0.00779 (11)0.00831 (17)00.00332 (15)0
Na30.01204 (15)0.01238 (10)0.01448 (16)00.00482 (13)0
C0.0071 (2)0.00690 (14)0.0072 (2)00.00232 (19)0
O10.01620 (17)0.00969 (10)0.01463 (16)0.00452 (10)0.00584 (14)0.00021 (10)
O20.00874 (19)0.01506 (15)0.0115 (2)00.00509 (17)0
(II) sodium carbonate top
Crystal data top
Na2CO3F(000) = 208
Mr = 106Dx = 2.536 Mg m3
Monoclinic, C2/m(αlpha0γamma)0sMelting point: 851 C K
q = 0.18200a* + 0.32200c*Mo Kα radiation, λ = 0.71073 Å
a = 8.9195 ÅCell parameters from 1610 reflections
b = 5.2454 Åθ = 10–43°
c = 6.05 ŵ = 0.49 mm1
β = 101.354°T = 295K K
V = 277.52 Å3Potato, white
Z = 40.5mm × 0.45mm × 0.4mm mm
† Symmetry operations: (1) x1, x2, x3, x4; (2) −x1, x2, −x3, 1/2−x4; (3) −x1, −x2, −x3, −x4; (4) x1, −x2, x3, 1/2+x4; (5) 1/2+x1, 1/2+x2, x3, x4; (6) 1/2−x1, 1/2+x2, −x3, 1/2−x4; (7) 1/2−x1, 1/2−x2, −x3, −x4; (8) 1/2+x1, 1/2−x2, x3, 1/2+x4.

Data collection top
Xcalibur
diffractometer
No. of measured, independent and observed reflections: 77868, 14118, 4178 [I > 3σ(I)]; 1155, 1155, 814 (Main); 2070, 2070, 1244 (Sat1); 2298, 2298, 1033 (Sat2); 2044, 2044, 595 (Sat3); 2284, 2284, 330 (Sat4); 2022, 2022, 113 (Sat5); 2245, 2245, 49 (Sat6)
Radiation source: X-ray tubeRint = 0.064, 0.046 (Main), 0.055 (Sat1), 0.106 (Sat2), 0.274 (Sat3), 0.727 (Sat4), 1.211 (Sat5), 1.396 (Sat6)
Graphite monochromatorθmax = 45.7°, θmin = 4.0°
Detector resolution: 8 pixels mm-1h = 1818
ο–scansk = 1010
Wave-vector determination: Refined with cell parametersl = 1212
Refinement top
Refinement on FWeighting scheme based on measured s.u.'s w = 1/(σ2(F) + 0.0001F2)
R[F2 > 2σ(F2)] = 0.045, wR(F2) = 0.057, S = 1.50; R[F2 > 2σ(F2)] = 0.0354, R(F2) = 0.0618 (); R[F2 > 2σ(F2)] = 0.0340, R(F2) = 0.0419 (); R[F2 > 2σ(F2)] = 0.0527, R(F2) = 0.0592 (); R[F2 > 2σ(F2)] = 0.0795, R(F2) = 0.1049 (); R[F2 > 2σ(F2)] = 0.1110, R(F2) = 0.1592 (); R[F2 > 2σ(F2)] = 0.2223, R(F2) = 0.4069 (); R[F2 > 2σ(F2)] = 0.7863, R(F2) = 0.8210 ()(Δ/σ)max = 0.0002
4129 reflectionsΔρmax = 0.54 e Å3
180 parametersΔρmin = 0.60 e Å3
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Na10000.01731 (11)
Na2000.50.01673 (11)
Na30.17055 (4)0.50.74801 (6)0.02554 (10)
C0.16446 (7)0.50.24914 (10)0.01155 (13)
O10.10159 (5)0.29384 (7)0.28535 (7)0.02607 (12)
O20.28987 (6)0.50.17757 (11)0.02274 (14)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Na10.01757 (18)0.01860 (15)0.01713 (19)00.00672 (16)0
Na20.01919 (19)0.01561 (15)0.01686 (19)00.00714 (17)0
Na30.02174 (16)0.02568 (14)0.0307 (2)00.00888 (16)0
C0.0111 (2)0.01219 (17)0.0119 (2)00.0037 (2)0
O10.0318 (2)0.01881 (14)0.0299 (2)0.00956 (13)0.01172 (18)0.00055 (13)
O20.0148 (2)0.0324 (3)0.0237 (3)00.0104 (2)0
 

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