Dication Containing Three Aromatic Ring Structure-Directs toward a Chiral Zeolite, Spans Three Cavities, and Effectively Traps Water

The chiral zeolite STW has been synthesized using a large dication containing three aromatic rings (two imidazolium moieties plus a benzene one). The integrity of the occluded organics is proven by 1H and 13C liquid NMR of the zeolite dissolved in HF/D2O. Molecular simulations strongly suggest that each aromatic ring is located in a different cavity so that each dication crosses two medium pore 10-membered-ring (MR) windows. This is confirmed by Rietveld refinement against synchrotron powder X-ray diffraction data, which suggests that there is also trapped water in the cavities, explaining a significant excess of H found in this material. The presence of water is very soundly confirmed by Fourier-transform infrared experiments, which also show that this water cannot leave the zeolite even after heating at 180 °C under vacuum. Molecular simulations allow us to conclude that this is due to the blockage of the 10 and 8MR windows by the occluded organics. The peculiar situation of an organic structure-directing agent spanning three cavities has important implications for the structure-direction concept that are briefly discussed. Several chiral derivatives of this dication have also been studied, and their possibility to enantioselectively direct the crystallization of STW has been analyzed.