Synthesis of CHA-Type Aluminophosphate Containing Penta-Coordinated Framework Aluminum Atoms

Abstract

Five different methylimidazolium cations were studied as organic structure-directing agents (OSDAs) in aluminophosphate (AlPO4) system in fluoride and hydroxide media, and a new CHA-type AlPO4 with unprecedentedly distorted structure (named as AlPO4-34P) has been synthesized using 1,3-dimethylimidazolium (13DMI) hydroxide. Its structure and location of encapsulated organic cations have been clearly elucidated from high resolution synchrotron X-ray powder diffraction data using the direct method and Rietveld analysis. This structure has penta-coordinated framework aluminum atoms connected by Al-OH-Al bridges, which has never been found in CHA-type structures. These findings were then corroborated using elemental analysis, solid-state MAS NMR, and FT-IR data.