10.1021/ja210703y.s001
Alex Rojas
Alex
Rojas
Luis Gómez-Hortigüela
Luis
Gómez-Hortigüela
Miguel A. Camblor
Miguel A.
Camblor
Zeolite Structure Direction
by Simple Bis(methylimidazolium)
Cations: The Effect of the Spacer Length on Structure Direction and
of the Imidazolium Ring Orientation on the <sup>19</sup>F NMR Resonances
American Chemical Society
2012
Zeolite Structure Direction
MFI
zeolite
19 F NMR ResonancesA series
Imidazolium Ring Orientation
19 F MAS NMR resonances
imidazolium ring
Periodic DFT calculations
19 F resonances
Molecular mechanics simulations support
6 methylene groups
2012-02-29 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Zeolite_Structure_Direction_by_Simple_Bis_methylimidazolium_Cations_The_Effect_of_the_Spacer_Length_on_Structure_Direction_and_of_the_Imidazolium_Ring_Orientation_on_the_sup_19_sup_F_NMR_Resonances/2545885
A series of doubly charged structure-directing agents
based on
two methylimidazolium moieties linked by a linear bridge of <i>n</i> = 3,4,5, or 6 methylene groups has been used in the synthesis
of pure silica zeolites in the presence of fluoride. All of them yielded
zeolite TON while only the one with <i>n</i> = 4 was able
to produce also zeolite MFI at highly concentrated conditions. In
this MFI zeolite, two distinct <sup>19</sup>F MAS NMR resonances with
about equal intensity were observed, indicating two different chemical
environments for occluded fluoride. With the singly charged 1-ethyl-3-methylimidazolium
cation, which can be formally considered as the “monomer”
of the bis-imidazolium cation with <i>n</i> = 4, TON and
MFI were also obtained, and again two <sup>19</sup>F MAS NMR resonances
now with largely dissimilar intensities were observed in MFI. Molecular
mechanics simulations support a commensurate structure-direction effect
for <i>n</i> = 4 in MFI, with each imidazolium ring, in
two different orientations, sitting close to the [4<sup>1</sup>5<sup>2</sup>6<sup>2</sup>] cage. Periodic DFT calculations suggest that
F in MFI resides always in the [4<sup>1</sup>5<sup>2</sup>6<sup>2</sup>] cages, with the different <sup>19</sup>F resonances observed being
due to the different orientation of the closest imidazolium ring.