ICP-2: A New Hybrid Organo-Inorganic Ferrierite Precursor with Expanded Layers Stabilized by π–π Stacking Interactions

Abstract

In this work we present the synthesis, characterization and molecular modeling of ICP-2, a new layered ferrierite precursor with expanded layers. ICP-2 is obtained in fluoride medium from aluminosilicate gels with low H 2 O content, using the chiral cation (1R,2S)-dimethylephedrinium (DMEP) as the organic structure-directing agent; ICP-2 can also be obtained as the Al-free form. The combination of physicochemical characterization of the material with molecular modeling indicates that ICP-2 is a layered material composed of ferrierite layers, where the organic cations play a dual 2 structural role through the formation of supramolecular aggregates. On the one hand, the organic cations stabilize the formation of the ferrierite layers with a core-shell structure, directing the formation of both the pseudo-10R channels (by supramolecular dimers aligned with the channel direction) and of the pseudo-cavities, with the trimethylammonium groups of DMEP fitting within. On the other hand, the aromatic rings of these organic cations in the pseudo-cavities develop π-π stacking interactions with equivalent cations in adjacent layers, holding together the ferrierite layers expanded at a distance of 20 Å, hence preventing the formation of H-bonds between the inorganic layers. The diastereoisomer (1S,2S)-dimethylpseudoephedrinium instead cannot direct the formation of ICP-2, which is explained because of its distinct conformational space which fits worse in the core-shell structure of ICP-2.

Two-Dimensional Zeolite Materials: Structural and Acidity Properties

“…ICP-2 can be obtained in fluoride medium from aluminosilicate gels, using the chiral cation (1R,2S)-dimethylephedrinium (DMEP) as the SDA. It is a core-shell structure where the shell is composed of the organic cations arranged as supramolecular dimers surrounding the inorganic FER cores [137]. Similar to PREFER, ICP-2 can also be obtained in an Al-free form.…”

Conformational Space of (1R,2S)-Dimethyl-Ephedrinium and (1S,2S)-Dimethyl-Pseudoephedrinium in the Synthesis of Nanoporous Aluminophosphates

“…36 On the other hand, we have recently also studied the structure-directing effect of (1R,2S)-dimethyl-ephedrinium and (1S,2S)-dimethyl-pseudoephedrinium for the synthesis of silica-based zeolite materials. 37 Interestingly, we found notable differences in the structure-directing behavior of the two closely-related diastereoisomers: the (1R,2S)-isomer was able to direct the crystallization of a layered crystalline precursor with ferrierite layers, while the (1S,2S)-isomer did not produce any crystalline material under the same conditions, despite their very similar molecular structure. These chiral cations combine a strong molecular asymmetry (due to the presence of 2 stereogenic centers) and a number of freely-rotating single bonds which provide a rich conformational space.…”

“…We have recently reported the crystallization of a ferrierite-related layered material using the same DMEP cation as SDA (ICP-1 and PREFER). 37 Molecular simulations showed that in these materials, DMEP cations prefer to site in conformation A (see Figure S18).…”

“…These chiral cations combine a strong molecular asymmetry (due to the presence of 2 stereogenic centers) and a number of freely-rotating single bonds which provide a rich conformational space. Indeed, it has been shown by us 37,38 and others [39][40][41] that the conformational behavior of organic SDAs can be crucial during the structuredirecting phenomenon of zeolite materials. Furthermore, diastereoisomerism can also have a strong influence on the crystallization path.…”

Advances in the Synthesis of Ferrierite Zeolite

“…Topotactic conversion condensation of layered precursors [38][39][40][41] As with many other important zeolites, the earliest and most common synthesis route for aluminosilicate FER zeolites is hydrothermal synthesis, which is performed at very high temperature (above 300 • C) in the presence of Na + -Ca 2+ , Ca 2+ -Sr 2+ -Na + or Na + -tetramethylammonium (TMA) composite [25,32]. Then, with the employment of new organic templates such as cetyltrimethylammonium, diethanolamine, pyrrolidine (THP) or ethylenediamine (EDA), the synthesis temperature could be reduced to around 150 • C [20,[33][34][35].…”