ChemInform Abstract: Nonferroic Ima2 → Pna21 (X(τ4)) Phase Transition in a SAPO‐II Type Silicoaluminophosphate Molecular Sieve. Structural Investigations on the “as‐Synthesized” (SYN), Calcined (CAL) and Cyclohexane Adsorbed (CYC) Forms.

Abstract

005ChemInform Abstract The calcined form of a polycrystalline material with H2Si2P18Al20O80 (I) composition crystallizes in the orthorhombic space group Pna21. Adsorption of cyclohexane at room temp. on the CAL form yields the CYC form ((I), 2 C6H12), which crystallizes back into the orthorhombic space group Ima2 of the SYN form. Therefore, the adsorption energy of cyclohexane on the low-symmetry nonferroic Pna21 framework is high enough to induce the reverse phase transition and stabilize the high-symmetry structure.