Small 51V chemical shift anisotropy for LaVO 4 from MQMAS and MAS NMR spectroscopy

Abstract

51V 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 δ σ (= δ iso– δ zz ) along with the asymmetry parameter ( η σ ) for a vanadium environment with a small CSA and a rather strong quadrupole coupling. This is demonstrated for the orthovanadate LaVO 4 for which 51V 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 δ σ . The CSA parameters are reliably obtained from analysis of the spinning sidebands observed in a 51V 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 51V quadrupole coupling and CSA tensors for LaVO 4.