Synthesis of 3D Large-Pore Germanosilicate Zeolites Using Imidazolium-Based Long Dications

Introduction of small molar fractions of Ge in a synthesis system otherwise yielding the monodimensional large-pore zeolite MTW produced three 3D large-pore materials as the Ge fraction increased: *BEA, HPM-8, and HPM-7. HPM-8 is a zeolite consisting of an intergrowth of polymorphs D and E of the zeolite Beta family with a large predominance (>80%) of polymorph D, according to DIFFaX simulations and high-resolution scanning transmission electron microscopy analysis. After calcination, HPM-8 becomes remarkably stable upon contact with ambient air. HPM-7 likely possesses the POS topology, which is related to polymorph C. The density of double 4-ring (D4R) units in the crystallized materials increases from *BEA to HPM-8 to HPM-7, that is, as the Ge fraction increases. Interestingly, molecular mechanics show that in both HPM-7 and HPM-8, the organic dications prefer to site with their imidazolium rings in close contact with the D4R units as a consequence of a stronger confinement in this position. Indeed, the structure-directing role of these long dications can be explained as a consequence of the appropriate distance match between adjacent D4R units in both zeolite frameworks (and hence the negative charges associated with the occluded fluoride) and the imidazolium rings of these organic dications (and hence the positive charges), which is dictated by the length of the alkyl spacers, thus driving the crystallization pathway toward these particular germanosilicate zeolites.