NMR-STUDY OF CROWN-ETHER MOTION IN 2 ALKALIDES

Nuclear spin-lattice relaxation times (T1) of both Cs-133 and Na-23 were measured as a function of temperature for two cesium sodides, Cs+(18-crown-6)2Na- and Cs+(15-crown-5)2Na-. A logarithmic dependence of the T1 values of these two compounds on the inverse temperature is interpreted as the result of crown ether rotational/conformational reorientation with average activation barriers of 31.2 and 35.4 kJ mol-1, respectively. This interpretation is supported by the line-width reduction of the Na-23 resonances, reduction of the observed Na-23 quadrupole coupling constants, and the disappearance of peaks in the powder X-ray diffraction patterns. The line-width data are used with the approximate formula of Waugh (Waugh, J. S.; Fedin, E. 1. Sov. Phys. Solid State 1963, 4, 1633) to yield activation barriers in good agreement with the nuclear spin-lattice relaxation analysis.