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There have been two previous structure determinations of the title compound, Na2WO4·2H2O: in 1969 [Mitra & Verma (1969). Indian J. Chem. 7, 598-602] and in 1974 [Okada et al. (1974a). Bull. Tokyo Inst. Technol. 120, 7-11]. However, both structures are incorrect according to their entries in the Inorganic Crystal Structure Database [(2007), URL: http://www.fiz-karlsruhe.de/ecid/Internet/en/DB/icsd/index.html]. Despite the high absorption coefficient, the H-atom positions could be observed and refined in the present study. Owing to the accurate analytical absorption correction, all non-H atoms could be refined satisfactorily with anisotropic displacement parameters. There are hydrogen-bonding inter­actions between all H atoms and the O atoms of the tungstate dianion.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807023355/mg2024sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536807023355/mg2024Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 291 K
  • Mean [sigma](W-O) = 0.003 Å
  • R factor = 0.021
  • wR factor = 0.053
  • Data-to-parameter ratio = 18.7

checkCIF/PLATON results

No syntax errors found



Alert level C PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ .... ? PLAT480_ALERT_4_C Long H...A H-Bond Reported H51 .. O3 .. 2.70 Ang.
Alert level G ABSTM02_ALERT_3_G The ratio of expected to reported Tmax/Tmin(RR) is > 2.00 Tmin and Tmax reported: 0.021 0.147 Tmin and Tmax expected: 0.003 0.131 RR = 6.378 Please check that your absorption correction is appropriate. PLAT794_ALERT_5_G Check Predicted Bond Valency for W1 (6) 5.86 PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints ....... 4
0 ALERT level A = In general: serious problem 0 ALERT level B = Potentially serious problem 2 ALERT level C = Check and explain 3 ALERT level G = General alerts; check 1 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 2 ALERT type 3 Indicator that the structure quality may be low 1 ALERT type 4 Improvement, methodology, query or suggestion 1 ALERT type 5 Informative message, check

Comment top

The two previous crystal structure determinations on sodium tungstate dihydrate (I) were undertaken more than 30 years ago. The first report, by Mitra & Verma (1969), was based on photographic data using Cu radiation. The second report (Okada et al., 1974a) was based on diffractometer data using Mo radiation, but both their entries in the Inorganic Crystal Structure Database (2007) indicate that there were problems with the deposited coordinates. In fact, the reported coordinates of Mitra & Verma (1969) are quite incorrect, while those of Okada et al.(1974a) have a single typographical error in the z-coordinate of O4 (which should read 0.5980). An anhydrous form of sodium tungstate has also been reported (Okada et al., 1974b).

The intensity data set for (I) was originally collected as test data for the absorption corrections in the WinGX suite of programs (Farrugia, 1999). The compound has a large linear absorption coefficient, µ(Mo—Kα) = 18.66 mm-1, and was readily available in suitable crystalline form. We report here the refinement using the data corrected for absorption by the analytical method (de Meulenaar & Tompa, 1965), as implemented in PLATON (Spek, 2003). The parameters most seriously affected by absorption errors are the anisotropic displacement parameters (adp's). In severe cases, the eigenvalues of the adp tensors may become negative (i.e. non-positive definite), but in the current case they all have very reasonable values. The largest ratio of maximum:minimum mean square atomic displacements is 2.22 for atom O2.

An ORTEP view of the asymmetric unit of (I) is shown in Figure 1. As expected, the [WO4]2- dianion has very nearly exact tetrahedral geometry. The small deviations presumably arise from the differing chemical environments of the oxygen atoms in the crystal lattice. Despite the high sample absorption, all hydrogen atoms could be detected in difference maps and were successfully refined. All these atoms are involved in H-bonds with oxygen atoms of the tungstate dianion, see Table and Figure 2. The hydrogen atom H51 forms a bifurcated H-bond with the oxygen atoms of two separate [WO4]2- anions, though one OH···O bond is relatively long. The other H-atoms are only involved in single classical H-bonds.

The Na+ ions occur together with the water molecules in layers parallel to the ac plane. These layers are separated by the [WO4]2- anions. The local coordination geometries of the two independent Na+ ions are quite distinct, see Figs. 3 and 4. The atom Na1 is approximately octahedrally coordinated by the oxygen atoms of two water molecules and four [WO4]2- anions, while Na2 is five-coordinate. The geometry is a very distorted trigonal bipyramid, with the atoms O1 and O5 occupying the axial positions, O1—Na2—O5 = 176.82 (13)°. However the O—W—O angles in the "equatorial" plane are very far from 120 °, and there is a relatively short non-bonded contact with a sixth oxygen atom, Na3···O5 = 3.607 (3) Å

Related literature top

For related literature, see: Farrugia (1999); Inorganic Crystal Structure Database (2007); Mitra & Verma (1969); Okada et al. (1974a,b); Sheldrick (1997); Spek (2003).

Experimental top

A commercial sample was used, and the crystals as received were adequate for the purpose.

Refinement top

The initial hydrogen atom positions were obtained from difference Fourier maps. They were refined with a common restrained O—H distance of 0.086 (2) Å and with a common Uiso of 0.050 (9), through the use of free variables in SHELXL (Sheldrick, 1997). The highest peak in the final difference map is at 0.0065 0.7968 0.0393 [0.87 Å from W1], and the deepest trough at 0.0748 0.1777 0.0243 [0.78 Å from W1].

Structure description top

The two previous crystal structure determinations on sodium tungstate dihydrate (I) were undertaken more than 30 years ago. The first report, by Mitra & Verma (1969), was based on photographic data using Cu radiation. The second report (Okada et al., 1974a) was based on diffractometer data using Mo radiation, but both their entries in the Inorganic Crystal Structure Database (2007) indicate that there were problems with the deposited coordinates. In fact, the reported coordinates of Mitra & Verma (1969) are quite incorrect, while those of Okada et al.(1974a) have a single typographical error in the z-coordinate of O4 (which should read 0.5980). An anhydrous form of sodium tungstate has also been reported (Okada et al., 1974b).

The intensity data set for (I) was originally collected as test data for the absorption corrections in the WinGX suite of programs (Farrugia, 1999). The compound has a large linear absorption coefficient, µ(Mo—Kα) = 18.66 mm-1, and was readily available in suitable crystalline form. We report here the refinement using the data corrected for absorption by the analytical method (de Meulenaar & Tompa, 1965), as implemented in PLATON (Spek, 2003). The parameters most seriously affected by absorption errors are the anisotropic displacement parameters (adp's). In severe cases, the eigenvalues of the adp tensors may become negative (i.e. non-positive definite), but in the current case they all have very reasonable values. The largest ratio of maximum:minimum mean square atomic displacements is 2.22 for atom O2.

An ORTEP view of the asymmetric unit of (I) is shown in Figure 1. As expected, the [WO4]2- dianion has very nearly exact tetrahedral geometry. The small deviations presumably arise from the differing chemical environments of the oxygen atoms in the crystal lattice. Despite the high sample absorption, all hydrogen atoms could be detected in difference maps and were successfully refined. All these atoms are involved in H-bonds with oxygen atoms of the tungstate dianion, see Table and Figure 2. The hydrogen atom H51 forms a bifurcated H-bond with the oxygen atoms of two separate [WO4]2- anions, though one OH···O bond is relatively long. The other H-atoms are only involved in single classical H-bonds.

The Na+ ions occur together with the water molecules in layers parallel to the ac plane. These layers are separated by the [WO4]2- anions. The local coordination geometries of the two independent Na+ ions are quite distinct, see Figs. 3 and 4. The atom Na1 is approximately octahedrally coordinated by the oxygen atoms of two water molecules and four [WO4]2- anions, while Na2 is five-coordinate. The geometry is a very distorted trigonal bipyramid, with the atoms O1 and O5 occupying the axial positions, O1—Na2—O5 = 176.82 (13)°. However the O—W—O angles in the "equatorial" plane are very far from 120 °, and there is a relatively short non-bonded contact with a sixth oxygen atom, Na3···O5 = 3.607 (3) Å

For related literature, see: Farrugia (1999); Inorganic Crystal Structure Database (2007); Mitra & Verma (1969); Okada et al. (1974a,b); Sheldrick (1997); Spek (2003).

Computing details top

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS86 (Sheldrick, 1985); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX publication routines (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. An ORTEP view of the asymmetric unit of (1). Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. An ORTEP view (50% probability ellipsoids) of the hydrogen bonding network between the [WO4]2- anions and the water molecules, in the plane perpendicular to the b axis. H-bonding interactions are drawn as dashed lines, and Na+ ions omitted for clarity. Symmetry codes: (viii) 1/2 + x, 3/2 - y, 1 - z; (ix) 1 - x, 1 - y, 1 - z; (x) -1/2 + x, 3/2 - y, 1 - z; (xiii) 1 - x, 1/2 + y, 3/2 - z; (xiv) 3/2 - x, 1/2 + y, z;
[Figure 3] Fig. 3. An ORTEP view (50% probability ellipsoids)of the local geometry around the atom Na1. Symmetry codes: (i) -1/2 + x, 3/2 - y, 1 - z; (ii) 1 - x, 1 - y, 1 - z; (iii) 1/2 - x, -1/2 + y, z;
[Figure 4] Fig. 4. An ORTEP view (50% probability ellipsoids) of the local geometry around the atom Na2 Symmetry codes: (i) 1/2 + x, 3/2 - y, 1 - z; (ii) 3/2 - x, -1/2 + y, z; (iii) 1/2 + x, y, 3/2 - z
(I) top
Crystal data top
Na2WO4.2H2ODx = 3.522 Mg m3
Mr = 329.86Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, PbcaCell parameters from 25 reflections
a = 8.4797 (5) Åθ = 21.1–24.9°
b = 10.5930 (5) ŵ = 18.66 mm1
c = 13.8527 (10) ÅT = 291 K
V = 1244.33 (13) Å3Plate, colourless
Z = 80.39 × 0.34 × 0.11 mm
F(000) = 1184
Data collection top
Enraf Nonius TurboCAD4
diffractometer
Rint = 0.027
Graphite monochromatorθmax = 30.0°, θmin = 2.9°
non–profiled ω/2θ scansh = 1111
Absorption correction: analytical
(de Meulenaer & Tompa, 1965; Alcock, 1970)
k = 114
Tmin = 0.021, Tmax = 0.148l = 1919
7543 measured reflections6 standard reflections every 120 min
1811 independent reflections intensity decay: 1%
1664 reflections with I > 2σ(I)
Refinement top
Refinement on F2All H-atom parameters refined
Least-squares matrix: full w = 1/[σ2(Fo2) + (0.023P)2 + 2.0063P]
where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.021(Δ/σ)max = 0.001
wR(F2) = 0.053Δρmax = 2.75 e Å3
S = 1.26Δρmin = 1.48 e Å3
1811 reflectionsExtinction correction: SHELXL
97 parametersExtinction coefficient: 0.00228 (11)
4 restraints
Crystal data top
Na2WO4.2H2OV = 1244.33 (13) Å3
Mr = 329.86Z = 8
Orthorhombic, PbcaMo Kα radiation
a = 8.4797 (5) ŵ = 18.66 mm1
b = 10.5930 (5) ÅT = 291 K
c = 13.8527 (10) Å0.39 × 0.34 × 0.11 mm
Data collection top
Enraf Nonius TurboCAD4
diffractometer
1664 reflections with I > 2σ(I)
Absorption correction: analytical
(de Meulenaer & Tompa, 1965; Alcock, 1970)
Rint = 0.027
Tmin = 0.021, Tmax = 0.1486 standard reflections every 120 min
7543 measured reflections intensity decay: 1%
1811 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0214 restraints
wR(F2) = 0.053All H-atom parameters refined
S = 1.26Δρmax = 2.75 e Å3
1811 reflectionsΔρmin = 1.48 e Å3
97 parameters
Special details top

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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
W10.513897 (17)0.801647 (13)0.522950 (10)0.01283 (7)
Na10.34357 (17)0.49523 (14)0.58520 (11)0.0210 (3)
Na20.74189 (16)0.54972 (15)0.64750 (12)0.0214 (3)
O10.4496 (3)0.8227 (3)0.4020 (2)0.0199 (5)
O20.5570 (3)0.6393 (2)0.54181 (19)0.0179 (5)
O30.6862 (3)0.8921 (3)0.5387 (2)0.0239 (6)
O40.3692 (3)0.8508 (3)0.6089 (2)0.0215 (5)
O50.5379 (4)0.4088 (3)0.6997 (2)0.0273 (6)
O60.2280 (3)0.6403 (3)0.7015 (2)0.0245 (6)
H510.584 (7)0.349 (4)0.669 (4)0.050 (9)*
H520.572 (7)0.395 (6)0.757 (3)0.050 (9)*
H610.136 (4)0.644 (6)0.676 (4)0.050 (9)*
H620.255 (7)0.715 (3)0.684 (5)0.050 (9)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
W10.01363 (9)0.01020 (10)0.01466 (10)0.00008 (4)0.00046 (4)0.00033 (4)
Na10.0215 (6)0.0170 (7)0.0245 (7)0.0023 (6)0.0010 (5)0.0016 (7)
Na20.0212 (7)0.0212 (7)0.0217 (7)0.0016 (6)0.0015 (5)0.0014 (6)
O10.0196 (11)0.0215 (12)0.0187 (13)0.0024 (10)0.0019 (10)0.0012 (10)
O20.0183 (11)0.0111 (11)0.0242 (12)0.0000 (10)0.0008 (10)0.0013 (10)
O30.0231 (12)0.0209 (13)0.0276 (14)0.0075 (11)0.0018 (10)0.0029 (12)
O40.0224 (12)0.0199 (12)0.0221 (13)0.0061 (10)0.0039 (10)0.0016 (11)
O50.0355 (14)0.0209 (14)0.0256 (14)0.0003 (12)0.0028 (12)0.0025 (12)
O60.0241 (13)0.0234 (14)0.0258 (14)0.0027 (11)0.0052 (11)0.0050 (12)
Geometric parameters (Å, º) top
W1—O31.761 (3)Na2—O22.346 (3)
W1—O11.776 (3)Na2—O52.396 (4)
W1—O21.778 (3)O1—Na2iii2.323 (3)
W1—O41.787 (3)O2—Na1ii2.416 (3)
Na1—O4i2.388 (3)O3—Na2vii2.331 (3)
Na1—O2ii2.416 (3)O3—Na1v2.480 (3)
Na1—O62.433 (3)O4—Na1viii2.388 (3)
Na1—O22.442 (3)O5—H510.86 (3)
Na1—O52.464 (4)O5—H520.86 (3)
Na1—O3iii2.480 (3)O6—Na2ix2.304 (3)
Na2—O6iv2.304 (3)O6—H610.86 (3)
Na2—O1v2.323 (3)O6—H620.86 (3)
Na2—O3vi2.331 (3)
O3—W1—O1107.66 (13)O6iv—Na2—O3vi154.00 (13)
O3—W1—O2109.73 (14)O1v—Na2—O3vi91.58 (11)
O1—W1—O2108.87 (12)O6iv—Na2—O2111.35 (11)
O3—W1—O4109.17 (13)O1v—Na2—O295.01 (11)
O1—W1—O4112.41 (12)O3vi—Na2—O293.50 (11)
O2—W1—O4108.97 (12)O6iv—Na2—O587.05 (12)
O4i—Na1—O2ii89.21 (10)O1v—Na2—O5176.82 (13)
O4i—Na1—O690.52 (11)O3vi—Na2—O586.42 (12)
O2ii—Na1—O6174.56 (12)O2—Na2—O587.59 (11)
O4i—Na1—O2173.66 (12)W1—O1—Na2iii125.75 (14)
O2ii—Na1—O286.02 (10)W1—O2—Na2128.35 (14)
O6—Na1—O293.83 (10)W1—O2—Na1ii122.37 (14)
O4i—Na1—O5100.30 (11)Na2—O2—Na1ii89.01 (10)
O2ii—Na1—O590.93 (11)W1—O2—Na1119.24 (13)
O6—Na1—O594.47 (11)Na2—O2—Na195.10 (10)
O2—Na1—O583.98 (11)Na1ii—O2—Na193.98 (10)
O4i—Na1—O3iii89.83 (11)W1—O3—Na2vii133.39 (16)
O2ii—Na1—O3iii88.15 (10)W1—O3—Na1v128.51 (15)
O6—Na1—O3iii86.42 (10)Na2vii—O3—Na1v87.82 (10)
O2—Na1—O3iii85.85 (10)W1—O4—Na1viii127.84 (15)
O5—Na1—O3iii169.82 (12)Na2—O5—Na193.26 (12)
O6iv—Na2—O1v93.69 (11)
Symmetry codes: (i) x+1/2, y1/2, z; (ii) x+1, y+1, z+1; (iii) x1/2, y+3/2, z+1; (iv) x+1/2, y, z+3/2; (v) x+1/2, y+3/2, z+1; (vi) x+3/2, y1/2, z; (vii) x+3/2, y+1/2, z; (viii) x+1/2, y+1/2, z; (ix) x1/2, y, z+3/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O5—H51···O1ii0.86 (3)2.09 (4)2.830 (4)145 (6)
O5—H52···O4x0.86 (3)1.98 (3)2.832 (4)174 (6)
O5—H51···O3vi0.86 (3)2.70 (6)3.237 (4)122 (5)
O6—H61···O1iii0.86 (3)1.95 (3)2.790 (4)167 (6)
O6—H62···O40.86 (3)2.02 (4)2.837 (4)159 (6)
Symmetry codes: (ii) x+1, y+1, z+1; (iii) x1/2, y+3/2, z+1; (vi) x+3/2, y1/2, z; (x) x+1, y1/2, z+3/2.

Experimental details

Crystal data
Chemical formulaNa2WO4.2H2O
Mr329.86
Crystal system, space groupOrthorhombic, Pbca
Temperature (K)291
a, b, c (Å)8.4797 (5), 10.5930 (5), 13.8527 (10)
V3)1244.33 (13)
Z8
Radiation typeMo Kα
µ (mm1)18.66
Crystal size (mm)0.39 × 0.34 × 0.11
Data collection
DiffractometerEnraf Nonius TurboCAD4
Absorption correctionAnalytical
(de Meulenaer & Tompa, 1965; Alcock, 1970)
Tmin, Tmax0.021, 0.148
No. of measured, independent and
observed [I > 2σ(I)] reflections
7543, 1811, 1664
Rint0.027
(sin θ/λ)max1)0.703
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.021, 0.053, 1.26
No. of reflections1811
No. of parameters97
No. of restraints4
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)2.75, 1.48

Computer programs: CAD-4 EXPRESS (Enraf-Nonius, 1994), CAD-4 EXPRESS, XCAD4 (Harms & Wocadlo, 1995), SHELXS86 (Sheldrick, 1985), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997), WinGX publication routines (Farrugia, 1999).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O5—H51···O1i0.86 (3)2.09 (4)2.830 (4)145 (6)
O5—H52···O4ii0.86 (3)1.98 (3)2.832 (4)174 (6)
O5—H51···O3iii0.86 (3)2.70 (6)3.237 (4)122 (5)
O6—H61···O1iv0.86 (3)1.95 (3)2.790 (4)167 (6)
O6—H62···O40.86 (3)2.02 (4)2.837 (4)159 (6)
Symmetry codes: (i) x+1, y+1, z+1; (ii) x+1, y1/2, z+3/2; (iii) x+3/2, y1/2, z; (iv) x1/2, y+3/2, z+1.
 

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