CS-133 CHEMICAL SHIELDING ANISOTROPIES AND QUADRUPOLE COUPLINGS FROM MAGIC-ANGLE-SPINNING NMR OF CESIUM SALTS

Magnitudes and relative orientations of Cs-133 quadrupole coupling and chemical shielding tensors have been accurately determined from Cs-13 3 magic-angle spinning (MAS) NMR spectra of the central and satellite transitions for four powdered cesium salts. Effects of small Cs-133 ch emical shielding anisotropies on the spectral appearance are observed in highly stabilized low-speed Cs-133 MAS NMR spectra and analyzed by iterative fitting and numerical error analysis of the complete manifol ds of spinning sidebands. Cs-133 MAS NMR spectra of the single Cs site for CsVO3 and CsClO4, recorded at different spinning speeds, give con sistent values for the parameters describing the two tensor interactio ns, while numerical error analysis of the spectra demonstrates that hi gh levels of accuracy can be obtained for all parameters employing low -speed MAS NMR. The performance of the method for powders containing m ultiple sites is demonstrated by the Cs-133 MAS spectra of Cs2CrO4 and Cs2SO4. The error limits for the Cs-133 MAS NMR data for Cs2CrO4 are similar to those reported in a recent single-crystal NMR study. Quadru pole coupling parameters and isotropic chemical shifts are reported fo r Cs2CO3 from a high-speed Cs-133 MAS spectrum. A linear correlation b etween Cs-133 quadrupole tensor elements and estimated EFG tensor elem ents from point-charge calculations, employing effective oxygen charge s, is reported and used to assign the NMR parameters for the two diffe rent crystallographic sites in Cs2CrO4, Cs2SO4, and Cs2CO4.