Accurate First-Principle Prediction of 29Si and 17O NMR Parameters in SiO2 Polymorphs: The Cases of Zeolites Sigma-2 and Ferrierite

Abstract: The magnetic shielding tensors of silica polymorphs have been investigated by meansof quantum chemical calculations. Several levels of theory, from Hartree-Fock to the lastgeneration of Density Functional Theory based approaches, have been tested on predicting29Si and 17O isotropic and principal components of the chemical shift tensors together with 17Oquadrupolar coupling constants. The NMR parameters have been computed on all known silicasystems, namely, R-quartz, R-cristobalite, coesite, Sigma-2, and ferrierite zeolites. Besides, clusterbased approaches have been compared to a hybrid Quantum-Mechanics/Molecular-Mechanics(QM/MM) method, within the ONIOM scheme. The convergence of computed 17O NMRparameters with respect to cluster size is found to be system-dependent. Excellent agreementbetween computed and experimental data has been found for 29Si NMR parameters of thedifferent Si sites of silica polymorphs and of Sigma-2 and ferrierite zeolites.