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.