⁵¹V MAS NMR Investigation of ⁵¹V Quadrupole Coupling and Chemical Shift Anisotropy in Divalent Metal Pyrovanadates

Abstract

Magnitudes and relative orientations of 51V quadrupole coupling and chemical shift tensors have been determined from 51V magic-angle spinning (MAS) NMR spectra at 14.1 T for seven divalent metal pyrovanadates: α- and β-Mg2V2O7, Ca2V2O7, α-Zn2V2O7, Cd2V2O7, BaCaV2O7, and α-BaZnV2O7. This has been accomplished by least-squares fitting of the integrated spinning sideband intensities observed for the central and satellite transitions employing spectral widths up to 4 MHz. Numerical error analysis of the optimized data reveals that the five NMR parameters characterizing the magnitudes of the quadrupole coupling and chemical shift tensors are obtained with high precision while somewhat larger error limits are observed for the three Euler angles, describing the relative orientation of the two tensors. The optimized data exhibit a significantly higher precision when compared to earlier reported parameters for some of the pyrovanadates, determined from 51V static-powder or MAS NMR of the central transition only. The 51V chemical shift parameters indicate that the different conformations for the V2O7 4- ion in thortveitite-type and dichromate-type pyrovanadates can be distinguished by the sign for the chemical shift anisotropy (δσ = δiso − δ zz ), negative and positive, respectively. A linear correlation is observed between the principal elements for the 51V quadrupole coupling tensors and calculated electric field gradient tensor elements, obtained from point−monopole calculations. This correlation is used to assign the NMR parameters for the two different crystallographic 51V sites in the asymmetric units for α- and β-Mg2V2O7, Ca2V2O7, BaCaV2O7, and α-BaZnV2O7.

51V magic angle spinning NMR in VOPO4 phases

“…The MAS spectra are observed to break up into spinning sidebands (ssbs) and the absence of significant quadrupolar secondorder shifts indicates that the quadrupole coupling constant Q CC D e 2 qQ/h is moderate (jQ CC j < 3 MHz). 1,2,22,23 Indeed, the good agreement between the experimental and calculated data (Figs 1 and 2) demonstrates that the complete manifolds of ssbs from all seven 51 V transitions are detected. For simplicity, in Figs 1 and 2, the isotropic peak, determined from spectra employing different spinning speeds, was arbitrarily chosen as the chemical shift reference.…”

Practical aspects of 51V and 93Nb solid-state NMR spectroscopy and applications to oxide materials

“…In pyrovanadates of divalent metals two vanadium atoms in V 2 51 V NMR parameters for many pyrovanadates of divalent metals have been reported by Nielsen et al [147].…”

“…and even several V-containing biological systems, have also recently been studied [93,94,[144][145][146][147][148][149]. It is noteworthy, that almost Table 4 Different types of vanadium sites all types of vanadium sites shown in Table 4 can be found in these individual compounds.…”

Synthesis, 89Y and 51V-NMR of Er-doped zircon-type YVO4 and LUVO4

“…catalysis [9] and electrochemistry [10]. Both monodimensional (MAS and SAtellite TRAnsition Spectroscopy, SATRAS) and two-dimensional (Multiple Quantum, MQMAS) experiments have been recently applied to the study of meta-, pyro-and ortho-vanadates [9,[11][12][13][14]. In particular, it has been shown that the NMR spectra of orthovanadates are dominated by electric quadrupolar interaction (the quadrupolar coupling constant, C Q ; spans between 1 and 6 MHz), whereas the chemical shift anisotropy (CSA) is less than 100 ppm, due to the almost spherically symmetric shielding tensor of the tetrahedral oxygen environment (Q 0 unit) [9,14].…”