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

ABSTRACT: Time-of-flight neutron powder diffraction data have been collected from Na2MoO4 and Na2WO4 to a resolution of sin?(?)/? = 1.25?Å(-1), which is substanti-ally better than the previous analyses using Mo K? 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.

SUBMITTER: Fortes AD 

PROVIDER: S-EPMC4459306 | biostudies-other | 2015 Jun

REPOSITORIES: biostudies-other