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Crystal structures of spinel-type Na2MoO4 and Na2WO4 revisited using neutron powder diffraction.

Fortes AD - Acta Crystallogr E Crystallogr Commun (2015)

Bottom Line: Anorg.Allg.However, the tungstate structure refinement of Okada et al. (1974 ▶) stands apart as being conspicuously inaccurate, giving significantly longer W-O distances, 1.819 (8) Å, and shorter Na-O distances, 2.378 (8) Å, than are reported here or in other simple tungstates.

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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 collected from Na2MoO4 and Na2WO4 to a resolution of sin (θ)/λ = 1.25 Å(-1), which is substanti-ally better than the previous analyses using Mo Kα X-rays, providing roughly triple the number of measured reflections with respect to the previous studies [Okada et al. (1974 ▶). Acta Cryst. B30, 1872-1873; Bramnik & Ehrenberg (2004 ▶). Z. Anorg. Allg. Chem. 630, 1336-1341]. The unit-cell parameters are in excellent agreement with literature data [Swanson et al. (1962 ▶). NBS Monograph No. 25, sect. 1, pp. 46-47] and the structural parameters for the molybdate agree very well with those of Bramnik & Ehrenberg (2004 ▶). However, the tungstate structure refinement of Okada et al. (1974 ▶) stands apart as being conspicuously inaccurate, giving significantly longer W-O distances, 1.819 (8) Å, and shorter Na-O distances, 2.378 (8) Å, than are reported here or in other simple tungstates. As such, this work represents an order-of-magnitude improvement in precision for sodium molybdate and an equally substantial improvement in both accuracy and precision for sodium tungstate. Both compounds adopt the spinel structure type. The Na(+) ions have site symmetry .-3m and are in octa-hedral coordination while the transition metal atoms have site symmetry -43m and are in tetra-hedral coordination.

No MeSH data available.


Raman spectra of Na2MoO4 (left) and Na2WO4 (right) in the range 0–1200 cm−1 (the full range of data to 4000 cm−1 is given in the electronic supplement). Band positions and vibrational assignments are indicated. For the tungstate these agree very well with literature values (e.g., Busey & Keller, 1964 ▶) whereas for the molybdate, these data show a systematic shift to lower frequencies by 3–4 wavenumbers with respect to published values (Luz Lima et al., 2010 ▶, 2011 ▶).
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fig4: Raman spectra of Na2MoO4 (left) and Na2WO4 (right) in the range 0–1200 cm−1 (the full range of data to 4000 cm−1 is given in the electronic supplement). Band positions and vibrational assignments are indicated. For the tungstate these agree very well with literature values (e.g., Busey & Keller, 1964 ▶) whereas for the molybdate, these data show a systematic shift to lower frequencies by 3–4 wavenumbers with respect to published values (Luz Lima et al., 2010 ▶, 2011 ▶).

Mentions: Raman spectra were acquired using a B&WTek i-Raman plus portable spectrometer; this device uses a 532 nm laser (37 mW power at the fiber-optic probe tip) to stimulate Raman scattering, which is measured in the range 170–4000 cm−1 with a spectral resolution of 3 cm−1. Data were collected in a series of 20 x 9 sec integrations for Na2MoO4 and 20 x 7 sec integrations for Na2WO4; after summation, the background was removed and peaks fitted using Pseudo-Voigt functions in OriginPro (OriginLab, Northampton, MA) (Fig. 4 ▶). These data are provided as an electronic supplement in the form of an ASCII file.


Crystal structures of spinel-type Na2MoO4 and Na2WO4 revisited using neutron powder diffraction.

Fortes AD - Acta Crystallogr E Crystallogr Commun (2015)

Raman spectra of Na2MoO4 (left) and Na2WO4 (right) in the range 0–1200 cm−1 (the full range of data to 4000 cm−1 is given in the electronic supplement). Band positions and vibrational assignments are indicated. For the tungstate these agree very well with literature values (e.g., Busey & Keller, 1964 ▶) whereas for the molybdate, these data show a systematic shift to lower frequencies by 3–4 wavenumbers with respect to published values (Luz Lima et al., 2010 ▶, 2011 ▶).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4459306&req=5

fig4: Raman spectra of Na2MoO4 (left) and Na2WO4 (right) in the range 0–1200 cm−1 (the full range of data to 4000 cm−1 is given in the electronic supplement). Band positions and vibrational assignments are indicated. For the tungstate these agree very well with literature values (e.g., Busey & Keller, 1964 ▶) whereas for the molybdate, these data show a systematic shift to lower frequencies by 3–4 wavenumbers with respect to published values (Luz Lima et al., 2010 ▶, 2011 ▶).
Mentions: Raman spectra were acquired using a B&WTek i-Raman plus portable spectrometer; this device uses a 532 nm laser (37 mW power at the fiber-optic probe tip) to stimulate Raman scattering, which is measured in the range 170–4000 cm−1 with a spectral resolution of 3 cm−1. Data were collected in a series of 20 x 9 sec integrations for Na2MoO4 and 20 x 7 sec integrations for Na2WO4; after summation, the background was removed and peaks fitted using Pseudo-Voigt functions in OriginPro (OriginLab, Northampton, MA) (Fig. 4 ▶). These data are provided as an electronic supplement in the form of an ASCII file.

Bottom Line: Anorg.Allg.However, the tungstate structure refinement of Okada et al. (1974 ▶) stands apart as being conspicuously inaccurate, giving significantly longer W-O distances, 1.819 (8) Å, and shorter Na-O distances, 2.378 (8) Å, than are reported here or in other simple tungstates.

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 collected from Na2MoO4 and Na2WO4 to a resolution of sin (θ)/λ = 1.25 Å(-1), which is substanti-ally better than the previous analyses using Mo Kα X-rays, providing roughly triple the number of measured reflections with respect to the previous studies [Okada et al. (1974 ▶). Acta Cryst. B30, 1872-1873; Bramnik & Ehrenberg (2004 ▶). Z. Anorg. Allg. Chem. 630, 1336-1341]. The unit-cell parameters are in excellent agreement with literature data [Swanson et al. (1962 ▶). NBS Monograph No. 25, sect. 1, pp. 46-47] and the structural parameters for the molybdate agree very well with those of Bramnik & Ehrenberg (2004 ▶). However, the tungstate structure refinement of Okada et al. (1974 ▶) stands apart as being conspicuously inaccurate, giving significantly longer W-O distances, 1.819 (8) Å, and shorter Na-O distances, 2.378 (8) Å, than are reported here or in other simple tungstates. As such, this work represents an order-of-magnitude improvement in precision for sodium molybdate and an equally substantial improvement in both accuracy and precision for sodium tungstate. Both compounds adopt the spinel structure type. The Na(+) ions have site symmetry .-3m and are in octa-hedral coordination while the transition metal atoms have site symmetry -43m and are in tetra-hedral coordination.

No MeSH data available.