Absence of limitations on the framework density and pore size of high-silica zeolites

Through atomistic optimizations of recently enumerated hypothetical frameworks, we demonstrate that in contrast with the experimental observation by Brunner and Meier (Brunner, G. O.; Meier, W. M. Nature 1989, 337, 146), there is theoretically no evidence for any topological, geometric, or energetic Zn constraint on framework density and pore size in siliceous zeolites. More specifically, we show that there are numerous very low-density and/or very large-pore siliceous materials with comparable energetics to currently synthesized materials. The experimentally observed limitations thus seem instead to stem from a far from complete experimental exploration of the siliceous zeolite structural landscape and might be related to the lack of suitably large and rigid template molecules to fill the enormous void volume. Self-assembly of organic molecules to form nanosized templates might therefore hold the key to low density and/or extra-large-pore frameworks.