51V chemical shielding and quadrupole coupling in ortho- and metavanadates from 51V MAS NR4R spectroscopy

The combined effect from the V-51 quadrupole coupling and chemical shielding anisotropy (CSA) has been characterized for five orthovanadates (Mg-3(VO4)(2), Zn-3(VO4)(2), BiVO4, TaVO5, NbVO5) and two metavanadates (RbVO3 and CsVO3) employing V-51 magic-angle spinning (MAS) NMR of the central and satellite transitions. Furthermore, five metavanadates studied earlier (MVO3 where M = Li, Na, NH4, Tl, K) have been reinvestigated using rotor-stabilized MAS NMR, which improves the reliability of the spinning sideband (ssb)intensities: The complete manifolds of ssbs from all seven single-quantum transitions, observed in the MAS NMR spectra, have been analyzed using least-squares fitting and numerical error analysis. The optimized data demonstrate that for the metavanadates the magnitudes of the quadrupole and shielding anisotropy tensors (i.e., C-Q, eta(Q), delta(sigma), eta( sigma ))and of the Euler angle, which relates the principal element of the two tensors, can be determined with high precision. Somewhat larger error limits are observed for the two other Euler angles. The orthovanadates generally possess small shielding anisotropies which lead to a reduced precision of the CSA asymmetry parameter (eta(sigma)) Relationships between the V-51 NMR data and structural parameters; crystal symmetries, and earlier reported correlations are discussed. Furthermore, linear correlations between the experimental principal elements of the 51V quadrupole coupling tensors and estimated electric-field gradient tenser elements from point-monopole calculations are reported for both the ortho- and metavanadates.