NMR Studies of Oxide Glass Structure

Immobilization of N-Heterocyclic Carbene Compounds: A Synthetic Perspective

“…This can be attributed to anisotropy effects or orientation-dependent interactions . Second, the NHC content in most of the supported compounds (except for self-supported NHC compounds) is much lower than that of the supporting material, with the result that the intensive resonance of the supporting material may cover or suppress the resonance of the NHC species. ,,,, In addition to 13 C NMR analysis, 29 Si NMR studies are another widely used diagnostic method for the characterization of silica-based materials. − 29 Si NMR can provide structural information not only about the supporting material but also about the immobilized NHC compounds by analysis of silicon series (e.g., T n = RSi­(OSi) n (OH) 3– n and Q n = Si­(OSi) n (OH) 4– n ) present in 29 Si NMR spectra. Tetraethyl orthosilicate (TEOS) is widely used as a silica source to prepare supporting materials for NHC compounds, and in many cases the observation of Q bands (Q 2 , Q 3 , and Q 4 ) ranging from δ = −90 ppm to δ = −120 ppm corresponds to those of condensed TEOS. ,,,,− Furthermore, the existence of T bands (T 1 , T 2 , and T 3 ) ranging from δ = −49 ppm to δ = −75 ppm suggests the presence of Si–C linkages, which are typically resulting from the hydrolysis and condensation of trialkoxysilyl groups, thus confirming the bonding of the NHC moiety to the support. ,,,,, Additionally, the type and ratio of Si resonances can provide further hints concerning the immobilization.…”

Cation field strength effects on high pressure aluminosilicate glass structure: Multinuclear NMR and La XAFS results

“…The method is generally quantitative, is sensitive to the short-range structure around a particular nuclide, and does not require long-range order. In particular, 27 Al, 29 Si, 23 Na,and 45 Sc NMR are useful for characterizing the coordination numbers and environments of Al, Si, Na, and Sc, while 17 O NMR can reveal network connectivity and modifier cation ordering, as summarized by several authors (Eckert, 1992;Stebbins 1995Stebbins , 2001Mackenzie and Smith, 2002).…”

Characterization of Phase Separation and Thermal History Effects in Magnesium Silicate Glass Fibers by Nuclear Magnetic Resonance Spectroscopy

“…High-resolution nuclear magnetic resonance (NMR) spectroscopy, including studies of 29 Si, has been widely applied to elucidate the short-to intermediate-range structure of silicate glasses. [13][14][15][16][17][18] However, the applicability of NMR in detecting and characterizing phase separation in glasses is much less widely appreciated. This method relies on the observation that in many or most silicates, the mechanism of nuclear spin-lattice relaxation for 29 Si (a dilute, spin-1/2 nuclide with a relatively low gyromagnetic ratio and natural abundance) is dominated by direct magnetic dipolar coupling between the nuclear spins and those of unpaired electronic spins in trace contents of paramagnetic ions.…”