Lanthanide Paramagnetic Probes for NMR Spectroscopic Studies of Fast Molecular Conformational Dynamics and Temperature Control. 18-Crown-6 Intramolecular Reorientation in Complexes of Cerium(III) Chelates

Abstract

By H-1 dynamic NMR method the conformational reorientation of the 18-crown-6 ether molecules in [(Ce(ptfa)(3)) (2)(18-crown- 6)] complexes has been experimentally studied in the CDCl 3 solution. The results of the present work demonstrate that there is a conformational dynamic processes in [(Ce(ptfa) 3) 2 (18-crown-6)] complex (with the activation free energy Delta G(double dagger) (320K) = 49 +/- 4 kJ/mol). It is conditioned by conformational reorientation of 18-crown-6 molecule. These complexes are promising to be subnanoscale NMR spectroscopic probes to determine the temperature in nonaqueous media.