DYNAMICS OF WATER IN THE ALUMINOPHOSPHATE MOLECULAR-SIEVE VPI-5 - A H-2 NMR-STUDY

The dynamic behavior of water in the channels of VPI-5 has been reexam ined in order to arrive at a motional model which applies throughout t he temperature range from 225 to 348 K. An earlier model is unsuccessf ul in part of this range. We show that there are at least two sites fo r the intracrystalline water; one is bound to framework aluminum and u ndergoes rotational motion about the Al-OH2 bond; the other site is a free site within the VPI-5 channels. The motion in this site is approx imately isotropic. The results show an interesting dynamic behavior in the temperature range 261-297 K and are discussed with reference to a six-site motional model, which includes a consideration of internal r otations of the water molecules.