V-51 CHEMICAL SHIELDING AND QUADRUPOLE COUPLING IN ORTHOVANADATE AND METAVANADATE FROM V-51 MAS NR4R SPECTROSCOPY

The combined effect from the V-51 quadrupole coupling and chemical shi elding anisotropy (CSA) has been characterized for five orthovanadates (Mg-3(VO4)(2), Zn-3(VO4)(2), BiVO4, TaVO5, NbVO5) and two metavanadat es (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 reinves tigated 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 NM R spectra, have been analyzed using least-squares fitting and numerica l error analysis. The optimized data demonstrate that for the metavana dates the magnitudes of the quadrupole and shielding anisotropy tensor s (i.e., C-Q, eta(Q), delta(sigma), eta( sigma ))and of the Euler angl e, which relates the principal element of the two tensors, can be dete rmined with high precision. Somewhat larger error limits are observed for the two other Euler angles. The orthovanadates generally possess s mall shielding anisotropies which lead to a reduced precision of the C SA asymmetry parameter (eta(sigma)) Relationships between the V-51 NMR data and structural parameters; crystal symmetries, and earlier repor ted correlations are discussed. Furthermore, linear correlations betwe en the experimental principal elements of the 51V quadrupole coupling tensors and estimated electric-field gradient tenser elements from poi nt-monopole calculations are reported for both the ortho- and metavana dates.