It is widely known that the properties of a zeolite in catalytic or ion-exchange applications depend largely on the crystal structure of the zeolite. When a catalytic process takes place in a porous system with dimensions in the range 3-12 , the reaction pathway is strongly influenced by framework geometry and the steric constraints are fundamental for driving the reaction towards the desired products. [1,2] Even though a few extra-large pore zeolites (with channel delimited by more than twelve tetrahedra) have recently been reported, such as CIT-5, [3] UTD-1, [4] or ECR-34 [5] (characterized by apertures of 18-membered rings), there are several possible applications that involve molecules larger than the pore dimensions of the available zeolites. To overcome this limitation, mesoporous molecular sieves MCM-41, MCM-48, and MCM-50, with pore dimensions larger (about 30-100 ) than those of conventional zeolites have been developed. [6] The alluminosilicates that belong to the mesoporous family M41S have a periodic pore structure (i.e., giving rise to coherent X-ray diffraction), whereas the silica walls are disordered and resemble more the structure of a glass. Unlike conventional zeolites, these materials are not strongly acidic, [7] but they do show promise as supports in other types of catalysts, such as olefin polymerization. [8] Layered zeolitic materials represent another option for treating large molecules. These materials have an advantage in that they combine the good thermal stability of zeolites with active sites of zeolitic nature easily accessible to reactants. In fact, layered zeolitic materials can be pillared or delaminated to produce high-surface-area materials with a majority of their active sites exposed at the crystal surface. [9][10][11] Nevertheless, so far, only a few structures of synthetic layered silicates have been reported, mainly for two reasons: 1) solution of the crystal structure by powder diffraction is a very challenging task and the small crystal size typically do not allow single-crystal X-ray diffraction experiments, piperazine silicate EU 19 being the only excellent exception; [12] 2) as a consequence of the stacking disorder, which occurs between the layers, the powder-diffraction patterns of a layered material often suffer from severe peak broadening that precludes structure solution.Notwithstanding the above difficulties, there has recently been an increased activity in the structure elucidation of layered materials. [13][14][15][16][17][18] Among these materials, those composed by single zeolite sheets like PREFER are particularly interesting, [16] which after calcination leads to the ordered 3D net of the FER-type zeolite. A very similar behavior was reported for the borosilicate named ERB-1, [19] isostructural to MCM-22, the precursor of which is layered in 2D, and the 3D network is formed upon calcination through the condensation of the silanol groups located on the layer surface. Other examples of layered zeolite precursors are EU 19, [12] precursor of the structurally ...
