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

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      High-precision structural parameters for Na 2MoO 4·2D 2O and Na 2WO 4·2D 2O are reported based on refinement of high-resolution time-of-flight neutron powder diffraction data. Complementary Raman spectra are also provided.


      Time-of-flight neutron powder diffraction data have been measured from ∼90 mol% deuterated isotopologues of Na 2MoO 4·2H 2O and Na 2WO 4·2H 2O 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 inter­atomic 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 NaO 5 and NaO 6 polyhedra that form layers parallel with (010) inter­leaved with planes of XO 4 ( X = Mo, W) tetra­hedra that are linked by chains of water mol­ecules 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 inter­action involving one of the water mol­ecules in the tungstate [Farrugia (2007 ). Acta Cryst. E 63, i142] is in fact an ordinary two-centred ‘linear’ hydrogen bond.

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      [a ]ISIS Facility, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0QX, England
      [b ]Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, England
      [c ]Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet Street, London WC1E 7HX, England
      Author notes
      Correspondence e-mail: andrew.fortes@
      Acta Crystallogr E Crystallogr Commun
      Acta Crystallogr E Crystallogr Commun
      Acta Cryst. E
      Acta Crystallographica Section E: Crystallographic Communications
      International Union of Crystallography
      01 July 2015
      17 June 2015
      17 June 2015
      : 71
      : Pt 7 ( publisher-idID: e150700 )
      : 799-806
      4518980 wm5172 10.1107/S2056989015011354 ACSECI S2056989015011354
      © A. Dominic Fortes 2015

      This is an open-access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

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