CESIUM-133 SINGLE-CRYSTAL NMR-STUDY OF CESIUM CHROMATE

Cesium-133 NMR spectra of a single crystal of Cs2CrO4 (space group Pnm a) were obtained as a function of crystal orientation in an applied ma gnetic field of 4.70 T and analyzed to provide the magnitudes and orie ntations of the Cs-133 chemical shielding and quadrupolar tensors for each of the two crystallographically distinct Cs sites. These NMR-char acterized nuclear sites have been assigned to the crystallographic sit es based on the local symmetry and results of a point-charge model of the electric field gradient tensors. The results indicate that the che mical shielding and quadrupolar interactions are not coincident for ei ther distinct Cs-133 nucleus in the crystal lattice. For each site, th e principal axis system of the Cs-133 chemical shielding tenser is ori ented along the crystallographic a, b, c axes, while the orientation o f the electric field gradient tenser deviates from these axes, by 7 de grees and 52 degrees in the crystallographic plane of symmetry. The Cs -133 chemical shielding tensors span spectral widths of the order of 3 00 ppm, which is comparable to the range of isotropic chemical shifts for this isotope.