ChemInform Abstract: Variable-Temperature 87Rb Magic-Angle Spinning NMR Spectroscopy of Inorganic Rubidium Salts

Abstract

Temperature dependencies of the 87Rb quadrupole coupling constants (CQ), asymmetry parameters (ηQ), and isotropic chemical shifts (δiso) have been observed and determined for RbCl, RbClO4, Rb2SO4, and RbNO3 from variable-temperature (VT) 87Rb magic-angle spinning (MAS) NMR spectra for the temperature range from about −100 to +165 °C. VT 87Rb multiple-quantum MAS NMR spectra of the trigonal form for RbNO3 have assisted the retrival of CQ, ηQ, and δiso for the three Rb sites of this phase. The results demonstrate that CQ(87Rb) and δiso(87Rb) are highly temperature-dependent for all samples over the studied temperature range. Linear correlations of δiso with temperature, corresponding to temperature coefficients in the range −0.014 to −0.036 ppm/°C (i.e., increasing shielding with increasing temperature), are observed for all samples. An exception is the Rb(2) site in Rb2SO4 for which a small linear decrease in shielding is observed with increasing temperature. For RbClO4 and Rb2SO4 the three CQ(87Rb) values...