Crystal structure of a synthetic high silica zeolite - ZSM-39

The crystal structure of a high silica zeolite ZSM-39, unit cell composition excluding residual water and occluded materials-(Na, tetramethylammonium ion, tetraethylammonium ion)(0.4)(AlO2)(0.4)(SiO2)(135.6), was determined by X-ray powder diffraction. The framework is pseudoface-centred, pseudocubic with alpha=19.36 +/- 0.02 angstrom and ideal symmetry Fd3m. The framework consists of a space-filling arrangement of pentagonal dodecahedra and hexakaidecahedra and is isostructural with the 17 angstrom cubic gas hydrate. The ZSM-39 framework is composed entirely of five- and six-rings which limits its sorptive and exchange properties. However, the large fraction of five-rings and the high Si/Al ratio (>40) impart a high thermal stability. ZSM-39 containing no aluminium constitutes the end member composition. Although ZSM-39 is the only synthetic zeolite analogue of a gas hydrate, we propose here two related hypothetical frameworks containing pentagonal dodecahedral cages.