Comparing cosine and sine functions for calculating the magnetic shielding of 29Si nuclei across siliceous zeolites

Rybakov, A.A.; Vercauteren, D.P.; Larin, A.V.

Авторы: Rybakov A.A., Vercauteren D.P., Larin A.V.
Журнал: Journal of Physical Chemistry C
Том: 127
Номер: 50
Год издания: 2023
Издательство: American Chemical Society
Местоположение издательства: United States
Первая страница: 24324
Последняя страница: 24338
DOI: 10.1021/acs.jpcc.3c04616
Аннотация: The relationship between the s-fraction of O orbitals, electronic density at the O lone pair, and Si-O-Si angles in the total magnetic shielding (29Si) of zeolite materials is typically approximated using the cos(<Si-O-Si>)/(cos(<Si-O-Si>) - 1) function, the <Si-O-Si> being the averaged Si-O-Si angle over the four O neighbors of Si. In this work, an analogous sin(<Si-O-Si>) dependence is introduced based on the approximation of the absolute O dipoles Q1(O) versus the Si-O-Si angle in five zeolite structures (BEA, FER, GOO, ZSM-12, and ZSM-57). The models, along with -quartz, were considered to evaluate the advantages of both effects on chemical shifts and chemical shift anisotropies, as measured for -quartz and ZSM-12. The decrease of O dipole with the Si-O-Si angle is usually interpreted as a variation of the electronic density at the O lone pairs. The dependence of Q1(O) versus sin(Si-O-Si) demonstrated a similar high level of accuracy for Q1(O) in the zeolites. The sin(<Si-O-Si>) function for the magnetic isotropic iso(29Si) chemical shifts was also demonstrated for some of the five structures. The final conclusion regarding the better approximation of the angular dependence of the (29Si) chemical shifts between four candidate functions is linked to the distribution of Si-O bond lengths in the zeolites.
Добавил в систему: Ларин Александр Владимирович

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Comparing cosine and sine functions for calculating the magnetic shielding of 29Si nuclei across siliceous zeolitesстатья

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