A 1H nuclear magnetic resonance study of the motion of cations in some clathrate hydrates of tetramethylammonium fluoride and hydroxides

Abstract

A temperature-dependence study of 1H spin–lattice relaxation time, T1, and differential thermal analysis experiments has been carried out for tetramethylammonium fluoride tetrahydrate, [2H]6deuteroxide trihydrate and hydroxide pentahydrate. Solid–solid phase transitions were located at 276 K, ca. 185 K, and 307 and 315 K, respectively, for these clathrates. From the 1H T1 study it was found for the first two clathrates that 1H T1 observed below room temperature is mostly determined by the motion of the cation and can be explained in terms of the general method in which motion of all 1H–1H vectors in the cation are assumed to be independent. For the pentahydrate, contribution to 1H T1 from the motion of water molecules forming cages could be observed clearly at higher temperatures above ca. 250 K, although 1H T1 determined below this temperature was mainly governed by the motion of the cation. The motional parameters for the cation in the clathrates were obtained.