Synthesis of Germanosilicate Zeolite HPM-12 Using a Short Imidazolium-based Dication: Structure-Direction by Charge-to-Charge Distance Matching
A short imidazolium based dication, with only three methylene units in the space linker, selectively directs the crystallization towards zeolite HPM-12 (*UOE) as long as there is enough germanium present in the synthesis gel. The integrity of the dication is proved by dissolution of the zeolite and 1H and 13C NMR spectroscopy, where significant effects of organic concentration and presence and concentration of HF need to be taken into account. In the as-made HPM-12 zeolite, a large shift of 9 ppm of one resonance in the 13C MAS NMR is due to the particular conformation of the dication imposed by confinement in the zeolite framework, as found by DFT calculations. The structure-directing ability of this kind of dications with varying length of the linker suggests that matching of the distance between positive charges (imidazolium moieties) and negative charges (double four rings in which fluoride resides) plays a crucial role during crystallization.