STRUCTURE OF SAPO-31 REFINED FROM SINGLE-CRYSTAL DIFFRACTION DATE - SUBSTITUTION OF P BY SI ESTABLISHED BY DIFFRACTION METHODS

SAPO-31 is a silicoaluminophosphate with an idealized composition Al9P 8SiHO36 and a crystal structure close to AlPO4-31, a microporous subst ance of zeolite framework topology ATO, M(r) = 1095.72, rhombohedral, hexagonal setting, space group R3BAR, a = 20.839 (2), c = 5.041 (1) an gstrom, V = 1886 (1) angstrom3, Z = 2, D(x) = 1.93 Mg m-3. mu(Mo Kalph a) = 0.72 mm-1, lambda(Mo Kalpha) = 0.71069 angstrom, F(000) = 1081, 2 440 single crystal X-ray intensities measured, 391 averaged unique int ensities, refinement on Absolute value of F, R = 0.051, wR = 0.018, in cluding all unobserved and weak F(hkl). A previous refinement based on synchrotron X-ray powder diffraction data for AlPO4-31 is confirmed w ith much higher precision. The Si atoms in SAPO-31 replace statistical ly part of the P atoms in the framework. This type of substitution has thus been established by X-ray diffraction methods for the first time in a microporous silicoaluminophosphates.