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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.


Raman spectra of Na2WO4·2H2O and Na2WO4·2D2O in the range 200–3900 cm−1. Band positions and vibrational assignments are indicated (see also Table 3 ▸). Vertical scales show intensities relative to ν1 (XO42−).
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fig5: Raman spectra of Na2WO4·2H2O and Na2WO4·2D2O in the range 200–3900 cm−1. Band positions and vibrational assignments are indicated (see also Table 3 ▸). Vertical scales show intensities relative to ν1 (XO42−).

Mentions: Raman spectra of Na2MoO4·2H2O and Na2MoO4·2D2O were first reported by Mahadevan Pillai et al. (1997 ▸); subsequently, Luz-Lima et al. (2010 ▸) and Saraiva et al. (2013 ▸) published the Raman spectra of Na2MoO4·2H2O and Na2WO4·2H2O as a function of temperature (13–300 K) and as a function of hydro­static pressure (to 5 GPa). Both compounds exhibit evidence of a ‘conformational change’ on cooling through 120 K: the molybdate appears to undergo two high-pressure phase transitions, one at 3 GPa and the second at 4 GPa; the tungstate apparently undergoes a high-pressure phase transition at 3.9 GPa. The Raman spectra reported here (Figs. 4 ▸ and 5 ▸ and Supporting information) agree well with data in the literature (Table 3 ▸). The large blue-shifts in the inter­nal vibrational frequencies of the deuterated water mol­ecule are similar to the square root of the D:H mass ratio; the small blue-shifts of most of the inter­nal modes of the tetra­hedral oxyanions are consistent with stronger hydrogen bonding in the deuterated species, as expected (cf. Scheiner & Čuma, 1996 ▸; Soper & Benmore, 2008 ▸).


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)

Raman spectra of Na2WO4·2H2O and Na2WO4·2D2O in the range 200–3900 cm−1. Band positions and vibrational assignments are indicated (see also Table 3 ▸). Vertical scales show intensities relative to ν1 (XO42−).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig5: Raman spectra of Na2WO4·2H2O and Na2WO4·2D2O in the range 200–3900 cm−1. Band positions and vibrational assignments are indicated (see also Table 3 ▸). Vertical scales show intensities relative to ν1 (XO42−).
Mentions: Raman spectra of Na2MoO4·2H2O and Na2MoO4·2D2O were first reported by Mahadevan Pillai et al. (1997 ▸); subsequently, Luz-Lima et al. (2010 ▸) and Saraiva et al. (2013 ▸) published the Raman spectra of Na2MoO4·2H2O and Na2WO4·2H2O as a function of temperature (13–300 K) and as a function of hydro­static pressure (to 5 GPa). Both compounds exhibit evidence of a ‘conformational change’ on cooling through 120 K: the molybdate appears to undergo two high-pressure phase transitions, one at 3 GPa and the second at 4 GPa; the tungstate apparently undergoes a high-pressure phase transition at 3.9 GPa. The Raman spectra reported here (Figs. 4 ▸ and 5 ▸ and Supporting information) agree well with data in the literature (Table 3 ▸). The large blue-shifts in the inter­nal vibrational frequencies of the deuterated water mol­ecule are similar to the square root of the D:H mass ratio; the small blue-shifts of most of the inter­nal modes of the tetra­hedral oxyanions are consistent with stronger hydrogen bonding in the deuterated species, as expected (cf. Scheiner & Čuma, 1996 ▸; Soper & Benmore, 2008 ▸).

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.