2H NMR line shapes have been obtained as a function of temperature for partially deuteriated 15-crown-5·Nal, 15-crown-5·NaCI04 and 21-crown-7·KI. Sudden changes in the line shapes above 330 K correspond to phase transitions: DSC shows transitions at 338, 347 K for 15-crown-5.NaI, and 356, 374, 383 K for 15-crown-5·NaCI04. The 2H NMR line shapes for the room temperature (RT) phases show the onset of a motion of the macrocycles above 200K, which is rapid a little above room temperature. Through detailed analysis of the complicated line shapes it has been shown that the most consistent interpretation of the dynamics in these RT phases is a 'merry-go-round' type of motion similar to that found for 18-crown-6 and 12-crown-4 complexes in which O-CH2-CH2 units exchange sites around the ring, simultaneously adjusting their conformation to fit the site. In the high-temperature phases of all three complexes all the ring atoms are dynamically equivalent. This can only happen through a combination of increased symmetry and disorder for which possible models have been devised.

Additional Metadata
Keywords 2H NMR, Crown ether complexes, Disorder, Dynamics
Journal Canadian Journal of Chemistry
Citation
Buchanan, G.W, Gerzain, M., & Ratcliffe, C.I. (1999). Symmetry, disorder, and dynamics in solid crown ether complexes: 2H NMR studies of 15-crown-5·NaI, 15-crown-5·NaCIO4, and 21-crown-7·KI. Canadian Journal of Chemistry, 77(11), 1911–1921.