Synthesis and Structural Characterization of the Aluminosilicate LZ-135, a Zeolite Related to ZSM-10

The aluminosilicate LZ-135 was one of the first zeolites to be prepared in the presence of two or more organic structure-directing agents (in this case, Me4N+ (TMA) and Et4N+ (TEA)) and was patented 20 years ago. However, the material was polycrystalline, and at the time, its aluminosilicate framework structure could not be determined. In view of the fact that methods of structure determination from powder diffraction data have developed considerably in the meantime, a fresh analysis of the problem was undertaken. High-resolution synchrotron powder diffraction data were collected on a calcined sample of LZ-135 (as synthesized composition ca. |Na26TMA6|[Si76Al32O216]), and the new powder charge-flipping structure-solution algorithm was applied. The framework structure (P63/mmc; a = 31.3830(2) Å, c = 7.6513(1) Å) was revealed immediately, and then the positions of the Na+ ions and a few water molecules were located in a series of difference electron density maps. The [001] projection of the framework structure is identical to that of ZSM-10 (P63/mmm), but the (up−down) orientations of the (Si,Al) tetrahedra, and therefore their connectivities, are different, and this leads to a distinctly different topology with two 1-dimensional, 12-ring channel systems with effective pore widths of ∼7.2 and 6.5 Å. The new framework has been assigned the framework type code LTF by the International Zeolite Association. The framework structures of LZ-135 and ZSM-10 are related to one another in the same way as are those of mazzite and zeolite L. Approximately 27.5 Na+ ions were located in six different sites, and all are coordinated to oxygen atoms of the framework. Twelve H2O molecules per unit cell are associated with one of the Na+ ion positions, where they serve to complete an octahedral coordination geometry around the ion, and 5.2 are located in the larger of the two 12-ring channels, where they make hydrogen-bonding contacts to framework oxygen atoms and are probably associated with protons.