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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.

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.


Neutron powder diffraction data for Na2MoO4·2D2O; red points are the observations, the green line is the calculated profile and the pink line beneath the diffraction pattern represents Obs−Calc. Vertical black tick marks report the expected positions of the Bragg peaks. The inset shows the data measured at short flight times (i.e. small d-spacings).
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fig6: Neutron powder diffraction data for Na2MoO4·2D2O; red points are the observations, the green line is the calculated profile and the pink line beneath the diffraction pattern represents Obs−Calc. Vertical black tick marks report the expected positions of the Bragg peaks. The inset shows the data measured at short flight times (i.e. small d-spacings).

Mentions: Time-of-flight neutron diffraction patterns were collected at 295 K using the High Resolution Powder Diffractometer, HRPD (Ibberson, 2009 ▸), at the ISIS spallation neutron source, Harwell Campus, Oxfordshire, UK. Data were acquired in the range of neutron flight times from 30–130 msec (equivalent to neutron wavelengths of 1.24–5.36 Å) for 15.17 hr from the molybdate and 14.40 hr from the tungstate, equivalent to 615 and 590 µAhr of integrated proton beam current, respectively. These data sets were normalized to the incident spectrum and corrected for detector efficiency by reference to a V:Nb -scattering standard and then subsequently corrected for the sample-specific and wavelength-dependent self-shielding using Mantid (Arnold et al., 2014 ▸: Mantid, 2013 ▸). In the case of the molybdate, the number density of the specimen was determined to be 3.28 mol nm−3, with a scattering cross section, allowing for the water being 9.1 mol % 1H, σscatt = 93.81 b and an absorption cross section, σabs = 3.66 b; for the tungstate, the number density was 3.01 mol nm−3, the scattering cross section, allowing for the water being 8.6 mol % 1H, σscatt = 94.19 b and σabs = 19.48 b. Diffraction data were exported in GSAS format and analysed with the GSAS/Expgui Rietveld package (Larsen & Von Dreele, 2000 ▸: Toby, 2001 ▸). The fitted diffraction data are shown in Figs. 6 ▸ and 7 ▸.


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)

Neutron powder diffraction data for Na2MoO4·2D2O; red points are the observations, the green line is the calculated profile and the pink line beneath the diffraction pattern represents Obs−Calc. Vertical black tick marks report the expected positions of the Bragg peaks. The inset shows the data measured at short flight times (i.e. small d-spacings).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig6: Neutron powder diffraction data for Na2MoO4·2D2O; red points are the observations, the green line is the calculated profile and the pink line beneath the diffraction pattern represents Obs−Calc. Vertical black tick marks report the expected positions of the Bragg peaks. The inset shows the data measured at short flight times (i.e. small d-spacings).
Mentions: Time-of-flight neutron diffraction patterns were collected at 295 K using the High Resolution Powder Diffractometer, HRPD (Ibberson, 2009 ▸), at the ISIS spallation neutron source, Harwell Campus, Oxfordshire, UK. Data were acquired in the range of neutron flight times from 30–130 msec (equivalent to neutron wavelengths of 1.24–5.36 Å) for 15.17 hr from the molybdate and 14.40 hr from the tungstate, equivalent to 615 and 590 µAhr of integrated proton beam current, respectively. These data sets were normalized to the incident spectrum and corrected for detector efficiency by reference to a V:Nb -scattering standard and then subsequently corrected for the sample-specific and wavelength-dependent self-shielding using Mantid (Arnold et al., 2014 ▸: Mantid, 2013 ▸). In the case of the molybdate, the number density of the specimen was determined to be 3.28 mol nm−3, with a scattering cross section, allowing for the water being 9.1 mol % 1H, σscatt = 93.81 b and an absorption cross section, σabs = 3.66 b; for the tungstate, the number density was 3.01 mol nm−3, the scattering cross section, allowing for the water being 8.6 mol % 1H, σscatt = 94.19 b and σabs = 19.48 b. Diffraction data were exported in GSAS format and analysed with the GSAS/Expgui Rietveld package (Larsen & Von Dreele, 2000 ▸: Toby, 2001 ▸). The fitted diffraction data are shown in Figs. 6 ▸ and 7 ▸.

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.