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Crystal structures of deuterated sodium molybdate dihydrate and sodium tungstate dihydrate from time-of-flight neutron powder diffraction.

Fortes AD - Acta Crystallogr E Crystallogr Commun (2015)

Bottom Line: Asian J.Acta Cryst.E63, i142] is in fact an ordinary two-centred 'linear' hydrogen bond.

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Affiliation: ISIS Facility, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0QX, England ; Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, England ; Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet Street, London WC1E 7HX, England.

ABSTRACT
Time-of-flight neutron powder diffraction data have been measured from ∼90 mol% deuterated isotopologues of Na2MoO4·2H2O and Na2WO4·2H2O at 295 K to a resolution of sin (θ)/λ = 0.77 Å(-1). The use of neutrons has allowed refinement of structural parameters with a precision that varies by a factor of two from the heaviest to the lightest atoms; this contrasts with the X-ray based refinements where precision may be > 20× poorer for O atoms in the presence of atoms such as Mo and W. The accuracy and precision of inter-atomic distances and angles are in excellent agreement with recent X-ray single-crystal structure refinements whilst also completing our view of the hydrogen-bond geometry to the same degree of statistical certainty. The two structures are isotypic, space-group Pbca, with all atoms occupying general positions, being comprised of edge- and corner-sharing NaO5 and NaO6 polyhedra that form layers parallel with (010) inter-leaved with planes of XO4 (X = Mo, W) tetra-hedra that are linked by chains of water mol-ecules along [100] and [001]. The complete structure is identical with the previously described molybdate [Capitelli et al. (2006 ▸). Asian J. Chem. 18, 2856-2860] but shows that the purported three-centred inter-action involving one of the water mol-ecules in the tungstate [Farrugia (2007 ▸). Acta Cryst. E63, i142] is in fact an ordinary two-centred 'linear' hydrogen bond.

No MeSH data available.


First and second coordination shell of Mo6+/W6+ in the title compounds, revealing differences in the environment of each apical O2− that are responsible for the variations in Mo–O and W–O bond lengths. Anisotropic displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii)  + x,  − y, 1 − z; (iii) − + x,  − y, 1 − z; (iv)  − x,  + y, z; (v)  − x,  + y, z; (vi) 1 − x,  + y, 1.5 − z.]
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fig1: First and second coordination shell of Mo6+/W6+ in the title compounds, revealing differences in the environment of each apical O2− that are responsible for the variations in Mo–O and W–O bond lengths. Anisotropic displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii)  + x,  − y, 1 − z; (iii) − + x,  − y, 1 − z; (iv)  − x,  + y, z; (v)  − x,  + y, z; (vi) 1 − x,  + y, 1.5 − z.]

Mentions: Na2MoO4·2H2O and Na2WO4·2H2O are isotypic, crystallizing in the ortho­rhom­bic space group Pbca; all atoms occupy general positions (Wyckoff sites 8c). Note that the atom labelling scheme and space-group setting used here follows Farrugia (2007 ▸); consequently there are some differences with respect to other literature sources, although equivalent contacts are referred to in Table 1 ▸ and Table 2 ▸. The X6+ ions (X = Mo, W) are tetra­hedrally coordinated by O2−, the Mo—O and W—O bond lengths varying slightly according to the type of coordination adopted by a particular apex: O1 and O4 are each coordinated to Na+ and each also accepts two hydrogen bonds; O2 is coordinated to three Na+ ions and O3 is coordinated to two Na+ ions (Fig. 1 ▸). In both title compounds, X–O1 and X–O4 are the longest contacts and X–O3 is the shortest contact in the tetra­hedral oxyanion. The mean Mo—O and W—O bond lengths are in good agreement with those found in the anhydrous crystals (Fortes, 2015 ▸). Furthermore, each of the absolute Mo—O bond lengths are identical (within error) to those found by Capitelli et al. (2006 ▸); the agreement in W—O bond lengths with Farrugia (2007 ▸) is marginally poorer.


Crystal structures of deuterated sodium molybdate dihydrate and sodium tungstate dihydrate from time-of-flight neutron powder diffraction.

Fortes AD - Acta Crystallogr E Crystallogr Commun (2015)

First and second coordination shell of Mo6+/W6+ in the title compounds, revealing differences in the environment of each apical O2− that are responsible for the variations in Mo–O and W–O bond lengths. Anisotropic displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii)  + x,  − y, 1 − z; (iii) − + x,  − y, 1 − z; (iv)  − x,  + y, z; (v)  − x,  + y, z; (vi) 1 − x,  + y, 1.5 − z.]
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4518980&req=5

fig1: First and second coordination shell of Mo6+/W6+ in the title compounds, revealing differences in the environment of each apical O2− that are responsible for the variations in Mo–O and W–O bond lengths. Anisotropic displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii)  + x,  − y, 1 − z; (iii) − + x,  − y, 1 − z; (iv)  − x,  + y, z; (v)  − x,  + y, z; (vi) 1 − x,  + y, 1.5 − z.]
Mentions: Na2MoO4·2H2O and Na2WO4·2H2O are isotypic, crystallizing in the ortho­rhom­bic space group Pbca; all atoms occupy general positions (Wyckoff sites 8c). Note that the atom labelling scheme and space-group setting used here follows Farrugia (2007 ▸); consequently there are some differences with respect to other literature sources, although equivalent contacts are referred to in Table 1 ▸ and Table 2 ▸. The X6+ ions (X = Mo, W) are tetra­hedrally coordinated by O2−, the Mo—O and W—O bond lengths varying slightly according to the type of coordination adopted by a particular apex: O1 and O4 are each coordinated to Na+ and each also accepts two hydrogen bonds; O2 is coordinated to three Na+ ions and O3 is coordinated to two Na+ ions (Fig. 1 ▸). In both title compounds, X–O1 and X–O4 are the longest contacts and X–O3 is the shortest contact in the tetra­hedral oxyanion. The mean Mo—O and W—O bond lengths are in good agreement with those found in the anhydrous crystals (Fortes, 2015 ▸). Furthermore, each of the absolute Mo—O bond lengths are identical (within error) to those found by Capitelli et al. (2006 ▸); the agreement in W—O bond lengths with Farrugia (2007 ▸) is marginally poorer.

Bottom Line: Asian J.Acta Cryst.E63, i142] is in fact an ordinary two-centred 'linear' hydrogen bond.

View Article: PubMed Central - HTML - PubMed

Affiliation: ISIS Facility, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0QX, England ; Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, England ; Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet Street, London WC1E 7HX, England.

ABSTRACT
Time-of-flight neutron powder diffraction data have been measured from ∼90 mol% deuterated isotopologues of Na2MoO4·2H2O and Na2WO4·2H2O at 295 K to a resolution of sin (θ)/λ = 0.77 Å(-1). The use of neutrons has allowed refinement of structural parameters with a precision that varies by a factor of two from the heaviest to the lightest atoms; this contrasts with the X-ray based refinements where precision may be > 20× poorer for O atoms in the presence of atoms such as Mo and W. The accuracy and precision of inter-atomic distances and angles are in excellent agreement with recent X-ray single-crystal structure refinements whilst also completing our view of the hydrogen-bond geometry to the same degree of statistical certainty. The two structures are isotypic, space-group Pbca, with all atoms occupying general positions, being comprised of edge- and corner-sharing NaO5 and NaO6 polyhedra that form layers parallel with (010) inter-leaved with planes of XO4 (X = Mo, W) tetra-hedra that are linked by chains of water mol-ecules along [100] and [001]. The complete structure is identical with the previously described molybdate [Capitelli et al. (2006 ▸). Asian J. Chem. 18, 2856-2860] but shows that the purported three-centred inter-action involving one of the water mol-ecules in the tungstate [Farrugia (2007 ▸). Acta Cryst. E63, i142] is in fact an ordinary two-centred 'linear' hydrogen bond.

No MeSH data available.