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ICP-2: A New Hybrid Organo-Inorganic Ferrierite Precursor with Expanded Layers Stabilized by π–π Stacking Interactions
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<sub>2</sub>O content, using the chiral cation (1<i>R</i>,2<i>S</i>)-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 structural role through the formation of supramolecular
aggregates. On 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 pseudocavities, with
the trimethylammonium groups of DMEP fitting within. On the other
hand, the aromatic rings of these organic cations in the pseudocavities
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
(1<i>S</i>,2<i>S</i>)-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