The templated synthesis and structure determination by synchrotron microcrystal diffraction of the novel small pore magnesium aluminophosphate STA-2†

Abstract

A novel microporous aluminophosphate, STA-2, has been prepared by hydrothermal synthesis in the presence of the rationally designed template, [(C₇H₁₃N)(CH₂)₄(NC₇H₁₃)]²⁺ and in the absence and presence of sodium ions. Using sodium ions in the preparation results in the synthesis of crystals of STA-2 up to 50 µm in dimension, of sufficient quality to be studied by the new technique of microcrystal diffraction at a synchrotron X-ray source and with an area detector. Phase STA-2 is found to have symmetry R, a = 12.726(2), c = 30.939(6) Å at 200 K. Structure solution reveals it to be a small pore solid of the family of structural polytypes made up by the stacking of six-membered Al₃P₃O₆ rings, and possesses the most complex regular stacking sequence of any such structure known, which can be represented as ABAACACCBCBB in the usual convention. The stacking sequence is controlled by the size and shape of the templating molecule, the position of which, determined from the single-crystal diffraction, makes a close fit with the organic framework. Compound STA-2 is stable to thermal removal of the template molecule and has potential as a solid acid catalyst.