VPI-5 AT 90-DEGREES-C - A SYNCHROTRON POWDER DIFFRACTION STUDY

The structure of the aluminophosphate molecular sieve VPI-5 at 90 degr ees C under sealed conditions has been investigated using synchrotron powder diffraction data. Variable temperature Al-27, P-31 and H-1 soli d-state NMR experiments were performed to verify that the VPI-5 sample used was comparable to those described in the literature. The refined structure confirms that the symmetry of VPI-5 changes from P6(3) in t he as-synthesized form to P6(3)cm (topochemical symmetry) upon heating in a closed container. The Al atom located between the fused Lt-rings remains octahedrally coordinated, but the well-ordered water structur e observed in the as-synthesized form of VPI-5 at room temperature doe s not exist at 90 degrees C. (C) 1998 Elsevier Science B.V. All rights reserved.