Small 51V chemical shift anisotropy for LaVO4 from MQMAS and MAS NMR spectroscopy

V-51 MQMAS NMR of the triple-quantum transitions is shown to be particularly useful in the determination of the sign and magnitude of the chemical shift anisotropy (CSA) parameter delta(sigma)(= delta(iso) - delta(zz)) along with the asymmetry parameter (eta(sigma)) for a vanadium environment with a small CSA and a rather strong quadrupole coupling. This is demonstrated for the orthovanadate LaVO4 for which V-51 magic-angle spinning (MAS) NMR of the central and satellite transitions at 14.1 T gives precise values for the quadrupole coupling parameters, however, an ambiguous sign for delta(sigma). The CSA parameters are reliably obtained from analysis of the spinning sidebands observed in a V-51 triple-quantum MAS experiment. Combining these data with least-squares analysis of the manifold of spinning sidebands in the single-pulse MAS NMR spectrum results in a precise determination of the magnitudes and relative orientation of the V-51 quadrupole coupling and CSA tensors for LaVO4. (C) 2002 Elsevier Science (USA). All rights reserved.