Hypothetical molecular sieve frameworks

There are various ways to describe the frameworks of molecular sieves and their enumeration. As the number of possible three-dimensional 4-connected nets is infinite, all enumerations reported so far have been derived by empirical methods, although many interesting and potentially viable structures, particularly with low framework density (rich in 3- and 4-membered rings), have been found as a result. It is likely that recent progress in mathematical tiling theory will lead to new advances in systematic enumeration not only to molecular sieves, but also of a variety of chemical structures.