Acta Cryst. (2007). E63, i142 [ doi:10.1107/S1600536807023355 ]
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.
A commercial sample was used, and the crystals as received were adequate for the purpose.
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].
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).
![[Figure 1]](./mg2024fig1thm.gif)
| Fig. 1. An ORTEP view of the asymmetric unit of (1). Displacement ellipsoids are drawn at the 50% probability level. |
![[Figure 2]](./mg2024fig2thm.gif)
| 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]](./mg2024fig3thm.gif)
| 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]](./mg2024fig4thm.gif)
| 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 |
| Na2WO4.2H2O | Dx = 3.522 Mg m−3 |
| Mr = 329.86 | Mo Kα radiation, λ = 0.71073 Å |
| Orthorhombic, Pbca | Cell parameters from 25 reflections |
| a = 8.4797 (5) Å | θ = 21.1–24.9° |
| b = 10.5930 (5) Å | µ = 18.66 mm−1 |
| c = 13.8527 (10) Å | T = 291 K |
| V = 1244.33 (13) Å3 | Plate, colourless |
| Z = 8 | 0.39 × 0.34 × 0.11 mm |
| F(000) = 1184 |
| Enraf Nonius TurboCAD4 diffractometer | Rint = 0.027 |
| graphite | θmax = 30.0°, θmin = 2.9° |
| non–profiled ω/2θ scans | h = −11→11 |
| Absorption correction: analytical (de Meulenaer & Tompa, 1965; Alcock, 1970) | k = −1→14 |
| Tmin = 0.021, Tmax = 0.148 | l = −19→19 |
| 7543 measured reflections | 6 standard reflections every 120 min |
| 1811 independent reflections | intensity decay: 1% |
| 1664 reflections with I > 2σ(I) |
| Refinement on F2 | All 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) = 0.053 | Δρmax = 2.75 e Å−3 |
| S = 1.26 | Δρmin = −1.48 e Å−3 |
| 1811 reflections | Extinction correction: SHELXL |
| 97 parameters | Extinction coefficient: 0.00228 (11) |
| 4 restraints |
| Na2WO4.2H2O | V = 1244.33 (13) Å3 |
| Mr = 329.86 | Z = 8 |
| Orthorhombic, Pbca | Mo Kα radiation |
| a = 8.4797 (5) Å | µ = 18.66 mm−1 |
| b = 10.5930 (5) Å | T = 291 K |
| c = 13.8527 (10) Å | 0.39 × 0.34 × 0.11 mm |
| 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 = 0.148 | θmax = 30.0° |
| 7543 measured reflections | 6 standard reflections every 120 min |
| 1811 independent reflections | intensity decay: 1% |
| R[F2 > 2σ(F2)] = 0.021 | All H-atom parameters refined |
| wR(F2) = 0.053 | Δρmax = 2.75 e Å−3 |
| S = 1.26 | Δρmin = −1.48 e Å−3 |
| 1811 reflections | Absolute structure: ? |
| 97 parameters | Flack parameter: ? |
| 4 restraints | Rogers parameter: ? |
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. |
| x | y | z | Uiso*/Ueq | ||
| W1 | 0.513897 (17) | 0.801647 (13) | 0.522950 (10) | 0.01283 (7) | |
| Na1 | 0.34357 (17) | 0.49523 (14) | 0.58520 (11) | 0.0210 (3) | |
| Na2 | 0.74189 (16) | 0.54972 (15) | 0.64750 (12) | 0.0214 (3) | |
| O1 | 0.4496 (3) | 0.8227 (3) | 0.4020 (2) | 0.0199 (5) | |
| O2 | 0.5570 (3) | 0.6393 (2) | 0.54181 (19) | 0.0179 (5) | |
| O3 | 0.6862 (3) | 0.8921 (3) | 0.5387 (2) | 0.0239 (6) | |
| O4 | 0.3692 (3) | 0.8508 (3) | 0.6089 (2) | 0.0215 (5) | |
| O5 | 0.5379 (4) | 0.4088 (3) | 0.6997 (2) | 0.0273 (6) | |
| O6 | 0.2280 (3) | 0.6403 (3) | 0.7015 (2) | 0.0245 (6) | |
| H51 | 0.584 (7) | 0.349 (4) | 0.669 (4) | 0.050 (9)* | |
| H52 | 0.572 (7) | 0.395 (6) | 0.757 (3) | 0.050 (9)* | |
| H61 | 0.136 (4) | 0.644 (6) | 0.676 (4) | 0.050 (9)* | |
| H62 | 0.255 (7) | 0.715 (3) | 0.684 (5) | 0.050 (9)* |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| W1 | 0.01363 (9) | 0.01020 (10) | 0.01466 (10) | 0.00008 (4) | 0.00046 (4) | 0.00033 (4) |
| Na1 | 0.0215 (6) | 0.0170 (7) | 0.0245 (7) | −0.0023 (6) | 0.0010 (5) | −0.0016 (7) |
| Na2 | 0.0212 (7) | 0.0212 (7) | 0.0217 (7) | −0.0016 (6) | 0.0015 (5) | −0.0014 (6) |
| O1 | 0.0196 (11) | 0.0215 (12) | 0.0187 (13) | 0.0024 (10) | −0.0019 (10) | 0.0012 (10) |
| O2 | 0.0183 (11) | 0.0111 (11) | 0.0242 (12) | 0.0000 (10) | 0.0008 (10) | 0.0013 (10) |
| O3 | 0.0231 (12) | 0.0209 (13) | 0.0276 (14) | −0.0075 (11) | −0.0018 (10) | −0.0029 (12) |
| O4 | 0.0224 (12) | 0.0199 (12) | 0.0221 (13) | 0.0061 (10) | 0.0039 (10) | 0.0016 (11) |
| O5 | 0.0355 (14) | 0.0209 (14) | 0.0256 (14) | −0.0003 (12) | −0.0028 (12) | 0.0025 (12) |
| O6 | 0.0241 (13) | 0.0234 (14) | 0.0258 (14) | −0.0027 (11) | −0.0052 (11) | 0.0050 (12) |
| W1—O3 | 1.761 (3) | Na2—O2 | 2.346 (3) |
| W1—O1 | 1.776 (3) | Na2—O5 | 2.396 (4) |
| W1—O2 | 1.778 (3) | O1—Na2iii | 2.323 (3) |
| W1—O4 | 1.787 (3) | O2—Na1ii | 2.416 (3) |
| Na1—O4i | 2.388 (3) | O3—Na2vii | 2.331 (3) |
| Na1—O2ii | 2.416 (3) | O3—Na1v | 2.480 (3) |
| Na1—O6 | 2.433 (3) | O4—Na1viii | 2.388 (3) |
| Na1—O2 | 2.442 (3) | O5—H51 | 0.86 (3) |
| Na1—O5 | 2.464 (4) | O5—H52 | 0.86 (3) |
| Na1—O3iii | 2.480 (3) | O6—Na2ix | 2.304 (3) |
| Na2—O6iv | 2.304 (3) | O6—H61 | 0.86 (3) |
| Na2—O1v | 2.323 (3) | O6—H62 | 0.86 (3) |
| Na2—O3vi | 2.331 (3) | ||
| O3—W1—O1 | 107.66 (13) | O6iv—Na2—O3vi | 154.00 (13) |
| O3—W1—O2 | 109.73 (14) | O1v—Na2—O3vi | 91.58 (11) |
| O1—W1—O2 | 108.87 (12) | O6iv—Na2—O2 | 111.35 (11) |
| O3—W1—O4 | 109.17 (13) | O1v—Na2—O2 | 95.01 (11) |
| O1—W1—O4 | 112.41 (12) | O3vi—Na2—O2 | 93.50 (11) |
| O2—W1—O4 | 108.97 (12) | O6iv—Na2—O5 | 87.05 (12) |
| O4i—Na1—O2ii | 89.21 (10) | O1v—Na2—O5 | 176.82 (13) |
| O4i—Na1—O6 | 90.52 (11) | O3vi—Na2—O5 | 86.42 (12) |
| O2ii—Na1—O6 | 174.56 (12) | O2—Na2—O5 | 87.59 (11) |
| O4i—Na1—O2 | 173.66 (12) | W1—O1—Na2iii | 125.75 (14) |
| O2ii—Na1—O2 | 86.02 (10) | W1—O2—Na2 | 128.35 (14) |
| O6—Na1—O2 | 93.83 (10) | W1—O2—Na1ii | 122.37 (14) |
| O4i—Na1—O5 | 100.30 (11) | Na2—O2—Na1ii | 89.01 (10) |
| O2ii—Na1—O5 | 90.93 (11) | W1—O2—Na1 | 119.24 (13) |
| O6—Na1—O5 | 94.47 (11) | Na2—O2—Na1 | 95.10 (10) |
| O2—Na1—O5 | 83.98 (11) | Na1ii—O2—Na1 | 93.98 (10) |
| O4i—Na1—O3iii | 89.83 (11) | W1—O3—Na2vii | 133.39 (16) |
| O2ii—Na1—O3iii | 88.15 (10) | W1—O3—Na1v | 128.51 (15) |
| O6—Na1—O3iii | 86.42 (10) | Na2vii—O3—Na1v | 87.82 (10) |
| O2—Na1—O3iii | 85.85 (10) | W1—O4—Na1viii | 127.84 (15) |
| O5—Na1—O3iii | 169.82 (12) | Na2—O5—Na1 | 93.26 (12) |
| O6iv—Na2—O1v | 93.69 (11) |
| Symmetry codes: (i) −x+1/2, y−1/2, z; (ii) −x+1, −y+1, −z+1; (iii) x−1/2, −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, y−1/2, z; (vii) −x+3/2, y+1/2, z; (viii) −x+1/2, y+1/2, z; (ix) x−1/2, y, −z+3/2. |
| D—H···A | D—H | H···A | D···A | D—H···A |
| O5—H51···O1ii | 0.86 (3) | 2.09 (4) | 2.830 (4) | 145 (6) |
| O5—H52···O4x | 0.86 (3) | 1.98 (3) | 2.832 (4) | 174 (6) |
| O5—H51···O3vi | 0.86 (3) | 2.70 (6) | 3.237 (4) | 122 (5) |
| O6—H61···O1iii | 0.86 (3) | 1.95 (3) | 2.790 (4) | 167 (6) |
| O6—H62···O4 | 0.86 (3) | 2.02 (4) | 2.837 (4) | 159 (6) |
| Symmetry codes: (ii) −x+1, −y+1, −z+1; (x) −x+1, y−1/2, −z+3/2; (vi) −x+3/2, y−1/2, z; (iii) x−1/2, −y+3/2, −z+1. |
| D—H···A | D—H | H···A | D···A | D—H···A |
| O5—H51···O1i | 0.86 (3) | 2.09 (4) | 2.830 (4) | 145 (6) |
| O5—H52···O4ii | 0.86 (3) | 1.98 (3) | 2.832 (4) | 174 (6) |
| O5—H51···O3iii | 0.86 (3) | 2.70 (6) | 3.237 (4) | 122 (5) |
| O6—H61···O1iv | 0.86 (3) | 1.95 (3) | 2.790 (4) | 167 (6) |
| O6—H62···O4 | 0.86 (3) | 2.02 (4) | 2.837 (4) | 159 (6) |
| Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1, y−1/2, −z+3/2; (iii) −x+3/2, y−1/2, z; (iv) x−1/2, −y+3/2, −z+1. |
The EPSRC is acknowledged for funding the purchase of an Enraf–Nonius CAD4 diffractometer.
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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