Clathrates and Inclusion Compounds

1998

J. Phys. Chem. B

Solid-state deuterium NMR spectroscopy is used to study the dynamics of organic molecules occluded in the as-synthesized high-silica tectosilicate nonasil. The nonasil samples are synthesized using trimethylalkylammonium structure-directing agents to determine the role of electrostatic interactions. Size effects are quantified by performing 2H NMR spin−lattice (T 1) relaxation experiments, and the mobility of the substituent alkyl groups is studied using 2H MAS NMR. The charge-compensating defect sites are characterized using 29Si and 1H NMR. The motion of the trimethylammonium group of the structure-directing agent is a composite motion of methyl group rotations and rotation about the nitrogen C 3 axis in all samples down to 190 K. The 2H T 1 and 2H MAS NMR results illustrate the steric confinement the nonasil cage exerts on the larger (C n ≥ C5) substituent alkyl groups. Isotropic motion is not observed for any of the structure-directing agents at 370 K, indicating strong organic−inorganic interactions. This is in sharp contrast to nonasil samples made with electrically neutral amines where rapid isotropic reorientation is observed at room temperature. These results have interesting implications in zeolite synthesis. For aluminosilicates synthesized with charged structure-directing agents, similar organic−inorganic interactions may allow for aluminum preferentially occupying specific framework sites. This could lead to tailoring the distribution of catalytic sites in zeolites based on the charge distribution of the structure-directing agent.

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Section: Introductionsupporting

confidence: 75%

Section: Introductionmentioning

confidence: 93%

Solid-State Deuterium NMR Studies of Organic Molecules in the Tectosilicate Nonasil

1998

J. Phys. Chem. B

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“…7 Our results show that none of the SDAs isotropically reorient in the nonasil cage, in contrast to nonasil samples made with the electrically neutral 2-aminopentane. 8 These results confirm the presence of strong Coloumbic forces between the cationic SDA and the defect site in the zeolite framework that cannot be overcome with the thermal energy available at temperatures of at least 370 K. The presence of strong organic-inorganic Coloumbic forces suggests that the charge center on the SDA could be spatially correlated to the charge-compensating defect in the zeolite framework. Here, using two-dimensional NMR correlation spectroscopy, we study this spatial correlation issue for the three all-silica tectosilicates nonasil (NON), SSZ-23, and ZSM-12 (MTW).…”

Section: Introductionsupporting

confidence: 56%

Spatial Ordering of Organic and Inorganic Charge Centers in As-Made High-Silica Zeolites Determined by Multidimensional {¹H} →²H CPMAS NMR Correlation Spectroscopy

1998

Chem. Mater.

Evidence is presented for the spatial ordering of the organic and inorganic charge centers in the as-made tectosilicates nonasil, SSZ-23, and ZSM-12. This result is based on twodimensional 2 H-{ 1 H} NMR correlation spectroscopy experiments, which show correlation between the silanol protons of the defect site and the N-methyl groups of the structuredirecting agent. The two-dimensional NMR spectra for all samples suggest that the deuterons of the methyl groups adjacent to the organic charge center are preferentially ordered relative to the defect site. Experiments performed on a sample synthesized in D 2 O are consistent with the interpretation of the two-dimensional NMR experiments. The results also suggest that Coloumbic organic-inorganic forces influence the location of the chargecompensating defect site in all-silica zeolites. Moreover, we suggest an additional role for certain cationic structure-directing agents in zeolite synthesis, controlling the location of T +3 atoms in the zeolite framework.

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“…2 In contrast, electrically neutral molecules used to synthesize nonasil and other clathrasils reorient isotropically in the clathrasil cages. 3 An unresolved issue of our earlier study was whether the charges on the organic molecule and the nonasil framework are spatially ordered. Here we present compelling evidence in support of the spatial correlation of the charge centers using two-dimensional 1 H-2 H CPMAS NMR correlation spectroscopy.…”

mentioning

confidence: 94%

“…2 None of the SDAs used isotropically reorient on the 2 H NMR time scale (∼10 -7 s), in contrast to nonasil samples made with electrically neutral amines. 3 The 1 H MAS NMR spectrum of high-silica nonasil synthesized with trimethylalkylammonium cations consists of a broad asymmetric line at ∼3 ppm due to the structure-directing agent fully resolved from a line at ∼10.5 ppm due to silanols hydrogen bonded to a siloxy group. There is also a Lorentzian line at 4.8 ppm due to water and a line at 5.5 ppm due either to water or additional silanol groups not engaged in strong hydrogen bonding.…”

mentioning

confidence: 99%

Spatial Correlation of Charge Centers in the Tectosilicate Nonasil Determined by Multidimensional {¹H} → ²H CPMAS NMR Correlation Spectroscopy

1998

J. Am. Chem. Soc.