Zeolites are crystalline inorganic solids formed by TO 4 tetrahedra (T = Si, P, Al, Ge, etc.) with a well-defined system of regular pores having diameters up to about 2 nm. [1,2] The possibility of tuning pore dimensions and framework compositions have made zeolites the most successful materials for applications in gas adsorption and separation and for catalysis. [3,4] Their uses have been further expanded [3] to microelectronics for preparing materials with low values of the high-frequency dielectric constant [5] or manufacturing encapsulated light-emitting devices (LEDs), [6] to medicine for diagnostic treatments [7] and controlled drug delivery, or for release of semiotics for controlling insect populations in agricultural uses. [8] Those applications often require structures with low framework densities, large internal volumes, and preferentially, extra-large pores. However, up to now, the number of known zeolites with a low framework density (FD 12) is almost negligible, and the number with extra-large pores (! 18-R) is also extremely small. [1] Computational methods can predict a large number of thermodynamically feasible new structures, and they can stimulate and inspire the discovery of new structures. [9][10][11] For example, Foster and Treacy [10] have used a symmetry-constrained intersite bond searching method and have generated more than two million structures. With that methodology, the authors predicted a series of thermodynamically feasible extra-large-pore zeolites. Deem et al. [11] have also modeled relatively large number of low density zeolites and were able to show that the low-energy and low-density materials also tend to have desirably large rings.Among the zeolite structures with extra large pores predicted by Foster and Treacy, there is one with 18 10 10-R pore topology that could be of particular interest for catalysis, as it combines an extra-large pore (18-R) for molecular accessibility with connected 10-R pores that can introduce shape-selectivity effects. Recently, the predicted zeolite was synthesized and named ITQ-33. [12] This zeolite has 3-R and D4R units in the structure, and was at the time the silicate-based zeolite with the lowest framework density (12.3.T/1000 3 ). The pore topology of this extra-large-pore zeolite presented quite unique and interesting catalytic properties: The pore accessibility to large molecules through the 18-R was combined with shape selectivity in the 10-R pores for the primary products formed. [13] In the same data base, Foster and Treacy also predicted an extra-large-pore zeolite that was closely related to ITQ-33 (Zeolite reference 191_4_1985). In that new structure, the 10-R pores of ITQ-33 were expanded to 12-R pores connecting the larger perpendicular 18-R channels. The result was a zeolite with 18 12 12 pore topology instead of the 18 10 10 for ITQ-33. In particular, along with D4R units, the new zeolite contains D3R units that have never been seen in synthesized zeolites, which could be related to geometric strains introduced in the framework ...