Lewis acidic aluminosilicates: synthesis, 27 Al MQ/MAS NMR, and DFT-calculated 27 Al NMR parameters

0583043 - ÚMCH 2025 RIV US eng J - Journal Article
Kejik, M. - Brus, Jiří - Jeremias, L. - Šimoníková, L. - Moravec, Z. - Kobera, Libor - Stýskalík, A. - Barnes, C. E. - Pinkas, J.
Lewis acidic aluminosilicates: synthesis, 27 Al MQ/MAS NMR, and DFT-calculated 27 Al NMR parameters.
Inorganic Chemistry. Roč. 63, č. 5 (2024), s. 2679-2694. ISSN 0020-1669. E-ISSN 1520-510X
Institutional support: RVO:61389013
Keywords : Lewis acidic * aluminosilicates * 27 Al ssNMR
OECD category: Polymer science
Impact factor: 4.6, year: 2022
Method of publishing: Open access
https://pubs.acs.org/doi/10.1021/acs.inorgchem.3c04035

Porous aluminosilicates are functional materials of paramount importance as Lewis acid catalysts in the synthetic industry, yet the participating aluminum species remain poorly studied. Herein, a series of model aluminosilicate networks containing [L–AlO3] (L = THF, Et3N, pyridine, triethylphosphine oxide (TEPO)) and [AlO4]− centers were prepared through nonhydrolytic sol–gel condensation reactions of the spherosilicate building block (Me3Sn)8Si8O20 with L–AlX3 (X = Cl, Me, Et) and [Me4N] [AlCl4] compounds in THF or toluene. The substoichiometric dosage of the Al precursors ensured complete condensation and uniform incorporation, with the bulky spherosilicate forcing a separation between neighboring aluminum centers. The materials were characterized by 1H, 13C, 27Al, 29Si, and 31P MAS NMR and FTIR spectroscopies, ICP-OES, gravimetry, and N2 adsorption porosimetry. The resulting aluminum centers were resolved by 27Al TQ/MAS NMR techniques and assigned based on their spectroscopic parameters obtained by peak fitting (δiso, CQ, η) and their correspondence to the values calculated on model structures by DFT methods. A clear correlation between the decrease in the symmetry of the Al centers and the increase of the observed CQ was established with values spanning from 4.4 MHz for distorted [AlO4]− to 15.1 MHz for [THF–AlO3]. Products containing exclusively [TEPO–AlO3] or [AlO4]− centers could be obtained (single-site materials). For L = THF, Et3N, and pyridine, the [AlO4]− centers were formed together with the expected [L–AlO3] species, and a viable mechanism for the unexpected emergence of [AlO4]− was proposed.
Permanent Link: https://hdl.handle.net/11104/0351081