NMR Crystallography of Zeolites: Refinement of an NMR-Solved Crystal Structure Using ab Initio Calculations of ²⁹Si Chemical Shift Tensors

Abstract

An NMR structure refinement method for the NMR crystallography of zeolites is presented and demonstrated to give an NMR-determined crystal structure for the zeolite Sigma-2 that is in very good agreement with the single-crystal X-ray diffraction structure. The Si coordinates of the zeolite framework were solved from 29Si double-quantum NMR data obtained at a low magnetic field strength (7.0 T) and the Si and O coordinates were subsequently refined using the principal components of 29Si chemical shift tensors experimentally measured at an ultrahigh-field (21.1 T) and calculated using ab initio quantum chemical methods.

Crystal Structure Based Design of Signal Enhancement Schemes for Solid-State NMR of Insensitive Half-Integer Quadrupolar Nuclei

“…The spectrum was obtained at 11.7 T using a 6 mm Varian probe and Bruker Avance III spectrometer and was referenced to NH 4 Cl at 0 ppm. The WURST-QCPMG pulse sequence 38 was used, with a methodology reported elsewhere.…”

“…A common approach is to compare experimentally determined parameters (e.g., isotropic chemical shifts, shielding anisotropies, quadrupolar coupling constants) [2][3][4][5][6] with those calculated from crystal structures using gauge-including projector augmented wave (GIPAW) methods, 7-10 which take into account the full periodicity of the crystal lattice. Structures used in these calculations can either have been determined using diffraction methods, [2][3][4][5][6] inferred from the NMR results [11][12][13] or computationally predicted. 14 SSNMR has several advantages over diffraction techniques, such as the ability to target specific nuclei.…”

Ultra-high resolution 17O solid-state NMR spectroscopy of biomolecules: A comprehensive spectral analysis of monosodium L-glutamate·monohydrate

“…1 H, 13 C, 15 N and 29 Si. [1][2][3][4] This is because high spectral resolution of spin-½ systems can be obtained from routine In contrast the quadrupole interaction often significantly broadens the NMR signal of nuclei with spin > ½. 5 This greatly hinders the spectral resolution, even under fast MAS, for a molecular system with multiple crystallographic sites preventing spectral assignment.…”

Recent developments in solid-state NMR spectroscopy of crystalline microporous materials

“…79,80 Initial work demonstrated that, using just basic information from diffraction (cell parameters and space group), a 29 Si MAS NMR spectrum and a series of Si-Si distance measurements (from two-dimensional homonuclear correlation experiments), it was possible to solve the framework structure of two zeolites (later identified as ITQ-4 and ferrierite). 81 Figure 4 shows an overview of the structure determination strategy used, along with examples of the 29 Si MAS and two-dimensional correlation spectra of ITQ-4.…”

“…In subsequent work, it was shown that by comparing experimental and calculated 29 Si chemical shift tensors (i.e., the isotropic and anisotropic components of the shielding interaction) improvement of the initial structural models was possible, with refinement of the exact atomic positions. 79,82 Calculations were performed initially using small clusters, and gave good agreement with experiment for optimised structural models, 79 but more recent work using a periodic GIPAW approach was shown to result in an improvement. 82 In perhaps the most impressive advance in this area, the methods described above have been adapted and improved to enable structure determination in zeolites even when the space group is not known.…”