Structure of SAPO-31 refined from single-crystal diffraction data: substitution of P by Si established by diffraction methods

Abstract

SAPO-31 is a silicoaluminophosphate with an idealized composition Al 9 P 8 SiHO 36 , and a crystal structure close to AlPO 4 -31, a microporous substance of zeolite framework topology ATO, M r =1095.72, rhombohedral, hexagonal setting, space group R3, a=20.839 (2), c=5.041 (1) A, V=1886 (1) A 3 , Z=2, D x =1.93 Mg m -3 , μ(Mo Kα)=0.72 mm -1 , λ(Mo Kα)=0.71069 A, F(000)=1081, 2440 single crystal X-ray intensities measured, 391 averaged unique intensities, refinement on |F|, R=0.051, wR=0.018, including all unobserved and weak F hkl . A previous refinement based on synchrotron X-ray powder diffraction data for AlPO 4 -31 is conirmed with much higher precision. The Si atoms in SAPO-31 replace statistically 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 silicoaluminophosphate