133Cs Chemical Shielding Anisotropies and Quadrupole Couplings from Magic-Angle Spinning NMR of Cesium Salts

Abstract

Magnitudes and relative orientations of 133Cs quadrupole coupling and chemical shielding tensors have been accurately determined from 133Cs magic-angle spinning (MAS) NMR spectra of the central and satellite transitions for four powdered cesium salts. Effects of small 133Cs chemical shielding anisotropies on the spectral appearance are observed in highly stabilized low-speed 133Cs MAS NMR spectra and analyzed by iterative fitting and numerical error analysis of the complete manifolds of spinning sidebands. 133Cs MAS NMR spectra of the single Cs site for CsVO3 and CsClO4, recorded at different spinning speeds, give consistent values for the parameters describing the two tensor interactions, while numerical error analysis of the spectra demonstrates that high levels of accuracy can be obtained for all parameters employing low-speed MAS NMR. The performance of the method for powders containing multiple sites is demonstrated by the 133Cs MAS spectra of Cs2CrO4 and Cs2SO4. The error limits for the 133Cs MAS NMR data for Cs2CrO4 are similar to those reported in a recent single-crystal NMR study. Quadrupole coupling parameters and isotropic chemical shifts are reported for Cs2CO3 from a high-speed 133Cs MAS spectrum. A linear correlation between 133Cs quadrupole tensor elements and estimated EFG tensor elements from point-charge calculations, employing effective oxygen charges, is reported and used to assign the NMR parameters for the two different crystallographic sites in Cs2CrO4, Cs2SO4, and Cs2CO3.