The structure of as-synthesized AIPO 4-16 determined by a new framework modeling method and Rietveld refinement of synchrotron powder diffraction data

Abstract

Synchrotron powder data on as-synthesized AIPO 4 -16 was indexed on a cubic cell with a = 13.3832(6) Å and systematic absences of hkl with h + k, h + I, k + I = odd and hhl with h + l = odd. The most probable space group is F 23 (#196), assuming alternation of the aluminum and phosphorus atoms. The framework topology was confirmed using a new “a priori” modeling method presuming the idealized space group Fm ovbar3 m (#225) with 40 chemically equivalent tetrahedral atoms per unit cell. The resulting framework topology is equivalent to J.V. Smith's theoretical net #214 and can be described as an idealized zunyite framework with complete tetrahedral occupancy, as originally proposed by D.W. Breck. This new framework topology (designated AST) is the third molecular sieve topology that is built from double 4-rings. The cavities contain the organic template, quinuclidine, which was successfully modeled as a disordered group. The largest pore opening is a 6-ring. The final Rietveld residuals are R(wp) = 0.192 and R(F) = 0.106.