The molecular behavior of 1,3,5-trioxane in a cyclophosphazene inclusion compound:: A 2H NMR study

Dynamic H-2 NMR techniques were employed to examine the ordering behavior and dynamics of perdeuterated 1,3,5-trioxane-d(6) in the inclusion compound with tris-(1,2-dioxyphenyl)-cyclotriphosphazene. The experimental data, obtained by variable-temperature line. shape studies, spin-spin and spin-lattice relaxation, and 2D exchange experiments between 30 and 370 K, were analyzed in a quantitative way by carrying out theoretical calculations on the basis of various motional models. At room temperature, highly mobile trioxane guests are observed. They undergo various overall and conformational motions that give rise to a substantial orientational disorder within the hexagonal cyclophosphazene channels. For the present inclusion compound, the following guest motions could be assigned: (i) molecular rotation about the molecular C-3-axis of the guests (rotational diffusion process), (ii) rotation about the host channel symmetry axis (3-fold jump process), (iii) overall fluctuation, and (iv) ring inversion. It could be shown that the two symmetry axes for rotational motions are oriented perpendicular to each other, that is, the C-3-axes of the trioxane guests are inclined at an angle of 900 with respect to the channel long axis. The activation energies for the overall rotations were found to be rather low with values of 10.0 and 10.9 kJ/mol for the motion about the C-3-axis and channel long axis, respectively. For the ring inversion process, an activation energy of 50.0 kJ/mol was derived that is almost identical with the values reported from previous solution NMR studies.