Silica-ZSM-22: synthesis and single crystal structure refinement

Using hydrothermal techniques the aluminium-free end member of ZSM-22 (silica-ZSM-22) has been synthesized in the presence of any one of the amines — ethylenediamine, diethylamine, triethylenetetramine or 1-aminobutane. Using a single crystal with diethylamine as the guest molecule the crystal structure has been refined to Rw = 0.056. Silica-ZSM-22, 24SiO2·(C2H5)2NH, crystallizes in space group Cmc21 with ao = 13.859(3) Å, bo = 17.420(4) Å and co = 5.038(2) Å. Its tetrahedral framework is isotypic with that of zeolites ZSM-22 and theta-1 whose structures have been derived from X-ray powder data. The SiO2 framework of silica-ZSM-22 contains five-, six- and ten-membered rings of [SiO4]-tetrahedra. Its one-dimensional channel system is made up by ten-membered rings running parallel to [001]. They are elliptical in cross section with free diameters of 4.7 and 5.5 Å. The framework topology is closely related to those of ZSM-23 and ZSM-48. The formation of different porous tectosilicate frameworks appears to be dependent on the synthesis temperature and the nature of guest substances added.