Limits...
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.

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.


Neutron powder diffraction data for Na2MoO4; 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 very short flight times (i.e., small d-spacing).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4459306&req=5

fig1: Neutron powder diffraction data for Na2MoO4; 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 very short flight times (i.e., small d-spacing).

Mentions: In the course of preparing deuterated specimens of the dihydrated and deca­hydrated forms of Na2MoO4 and Na2WO4 for neutron diffraction analysis, the anhydrous phases were synthesised and an opportunity arose to acquire neutron powder diffraction data. The advantage of using a neutron radiation probe is that the scattering lengths of the atoms concerned are fairly similar, coherent scattering lengths being 6.715 fm for Mo, 4.86 fm for W, 3.63 fm for Na and 5.803 fm for O (Sears, 2006 ▶). Secondly, with the time-of-flight method, particularly with a very long primary flight path and high-angle backscattering detectors, one can acquire unparalleled resolution at very short flight times (i.e., small d-spacings), ensuring an order of magnitude improvement in parameter precision over the previous studies. In this work, usable data were obtained at a resolution of sin (θ)/λ = 1.25 Å−1, roughly tripling the number of measured reflections with respect to Okada et al. (1974 ▶) and Bramnik & Ehrenberg (2004 ▶). This work provides the most accurate and precise foundation on which to build future discussion of the hydrated forms of Na2MoO4 and Na2WO4. Neutron powder diffraction data for Na2MoO4 and Na2WO4 are given in Figs. 1 ▶ and 2 ▶.


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

Fortes AD - Acta Crystallogr E Crystallogr Commun (2015)

Neutron powder diffraction data for Na2MoO4; 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 very short flight times (i.e., small d-spacing).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig1: Neutron powder diffraction data for Na2MoO4; 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 very short flight times (i.e., small d-spacing).
Mentions: In the course of preparing deuterated specimens of the dihydrated and deca­hydrated forms of Na2MoO4 and Na2WO4 for neutron diffraction analysis, the anhydrous phases were synthesised and an opportunity arose to acquire neutron powder diffraction data. The advantage of using a neutron radiation probe is that the scattering lengths of the atoms concerned are fairly similar, coherent scattering lengths being 6.715 fm for Mo, 4.86 fm for W, 3.63 fm for Na and 5.803 fm for O (Sears, 2006 ▶). Secondly, with the time-of-flight method, particularly with a very long primary flight path and high-angle backscattering detectors, one can acquire unparalleled resolution at very short flight times (i.e., small d-spacings), ensuring an order of magnitude improvement in parameter precision over the previous studies. In this work, usable data were obtained at a resolution of sin (θ)/λ = 1.25 Å−1, roughly tripling the number of measured reflections with respect to Okada et al. (1974 ▶) and Bramnik & Ehrenberg (2004 ▶). This work provides the most accurate and precise foundation on which to build future discussion of the hydrated forms of Na2MoO4 and Na2WO4. Neutron powder diffraction data for Na2MoO4 and Na2WO4 are given in Figs. 1 ▶ and 2 ▶.

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.