Publication: Comparing quantum chemical calculation methods for structural investigation of zeolite crystal structures by solid-state NMR spectroscopy
All || By Area || By Year| Title | Comparing quantum chemical calculation methods for structural investigation of zeolite crystal structures by solid-state NMR spectroscopy | Authors/Editors* | D. H. Brouwer, I. L. Moudrakovski, R. J. Darton, R. E. Morris |
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| Where published* | Magnetic Resonance in Chemistry |
| How published* | Journal |
| Year* | 2010 |
| Volume | |
| Number | |
| Pages | |
| Publisher | Wiley |
| Keywords | solid-state NMR, zeolites, NMR crystallography, chemical shielding tensors, quantum chemical calculations |
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| Abstract |
Combining quantum chemical calculations and ultrahigh-field NMR measurements of 29Si chemical shielding tensors has provided a powerful approach for probing the fine details of zeolite crystal structures. In previous work, the quantum chemical calculations have been performed on âmolecular fragmentsâ extracted from the zeolite crystal structure using Hartree-Fock methods (as implemented in Gaussian). Using recently acquired ultrahigh-field 29Si NMR data for the pure silica zeolite ITQ-4, we report the results of calculations using recently developed quantum chemical calculation methods for periodic crystalline solids (as implemented in CASTEP) and compare these calculations to those calculated with Gaussian. Furthermore, in the context of NMR crystallography of zeolites, we report the completion of the NMR crystallography of the zeolite ITQ-4 which was previously solved from NMR data. We compare three options for the ârefinementâ of zeolite crystal structures from âNMR-solvedâ structures: (i) a simple target distance based geometry optimization, (ii) refinement of atomic coordinates in which the differences between experimental and calculated 29Si chemical shielding tensors are minimized, and (iii) refinement of atomic coordinates to minimize the total energy of the lattice using CASTEP quantum chemical calculations. All three refinement approaches give structures that are in remarkably good agreement with the single crystal XRD structure of ITQ-4. |
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