Fluoride Ion Entrapment in Octasilsesquioxane Cages as Models for Ion Entrapment in Zeolites. Further Examples, X-ray Crystal Structure Studies, and Investigations into How and Why They May Be Formed

Abstract

Two fluoride-encapsulated octasilsesquioxane cage compounds have been prepared using the TBAF route as important molecular models for studying ion entrapment in siliceous zeolites. Analyses by X-ray crystal structure and solution 19F/29Si NMR spectroscopy reveal very similar environments for the encapsulated fluoride ion perfectly centered within each cage with evidence of weak silicon−fluoride ion interactions. By comparing our NMR and X-ray data with those of nonencapsulated cage analogues from the literature, we observe the effect the fluoride ion has on the geometry of the cage and use the findings of related studies in the literature to suggest reasons fluoride ion may be becoming entrapped in the silsesquioxane core.

Nonclassical forces: Seemingly insignificant but a powerful tool to control macromolecular structures

“…More specific to the Si atom, there were some studies focused on the very weak Si/X (F, N, O) interaction also. [52][53][54][55][56][57] Unlike carbon compounds, organosilicon compounds have the potential to increase their coordination number to 5-and 6-coordinated Si centers and have been characterized by X-ray and nuclear magnetic resonance (NMR) spectroscopy. [58][59][60] Unfortunately, the weak Si/X interactions reported for stabilizing the particular conformations of small molecules in these pseudocoordinations are difficult to characterize by routine spectroscopic methods.…”

ESI and MALDI mass spectrometry of large POSS oligomers

“…To facilitate the observation of higher POSS oligomers we have had to develop new strategies to enhance cationization (or anionization) efficiency. Certain POSS monomers [35,36] efficiently incorporate fluoride ion into the cage center to produce ionic species so we investigated fluoride as a structural probe. This proved successful only for POSS monomers containing R-groups which are electron-withdrawing or have delocalized electron density.…”

New insights on organosilane oligomerization mechanisms using ESI-MS and 29Si NMR

“…NaCl addition was carried out just before ESI-MS analysis in order to avoid potential effects of this salt on the chemical speciation. [36][37][38] (Fig. 1).…”