Crystal structure of α-Mg2V2O7 from synchrotron X-ray powder diffraction and characterization by 51V MAS NMR spectroscopy

Abstract

The crystal structure of the low-temperature form of magnesium pyrovanadate (Mg₂V₂O₇) has been determined from synchrotron X-ray powder diffraction data using Rietveld refinement. α-Mg₂V₂O₇ is isostructural with Co₂V₂O₇ and Ni₂V₂O₇. The Mg²⁺ ions are octahedrally coordinated to oxygen atoms in a distorted arrangement while the pyrovanadate anion has an approximately eclipsed conformation of non-bridging oxygen atoms. The ⁵¹V MAS NMR spectra of the central and satellite transitions for the two distinct ⁵¹V sites in α-Mg₂V₂O₇ allow determination of the magnitudes and relative orientations of the ⁵¹V quadrupole coupling and chemical shift tensors. The crystal structure data are used to calculate the principal elements of the ⁵¹V electric field gradient tensors employing the point-monopole approach. A good correlation between these elements and the experimental ⁵¹V quadrupole tensor elements is observed, which allows assignment of the quadrupole coupling constants of C_Q  = 4.80 MHz and C_Q  = 3.33 MHz to the crystallographic V(1) and V(2) sites, respectively.