Solid-State 29Si NMR

When different Si(nM) sites (n = 0—4) can be resolved in the 29Si solid state NMR spectra of tetrahedral framework silicates, then the Si/M ratio can be determined by the equation [21]... 

Figure 2 shows 29Si solid state NMR data of high-silica ZSM-5 with 24 crystallographic Si positions, 15 of which are well enough resolved in the MAS NMR spectrum to be assigned to crystallographic positions. The CSA parameters are determined by simulation of the lineshapes of the powder pattern as obtained from the 2D experiment. 

The CP/MAS-29Si solid state NMR spectrum of 6a proves the presence of six crystallographically (and chemically) different 29Si nuclei, of which two sorts coincide (Fig. 15). It is noteworthy that the 7Li NMR spectrum of 6a in solution (Fig. 16) showed the expected distinction of four Li sorts The two singlets at S = 1.78 and 1.56 correspond... 

H, 2H and 29Si solid state NMR study of guest acetone molecules occupying the zeolitic channels of partially dehydrated sepiolite clay... 

H, 2H and 29Si Solid State NMR Study of Guest Acetone Molecules Occupying the 551 Zeolitic Channels of Partially Dehydrated Sepiolite Clay M.R. Weir, G.A. Facey and C. Detellier... 

FIGURE 6. CP MAS 29Si solid state NMR spectrum showing the different level of condensation of xerogels p-Oi sSiCIHCTECfil I4OI2CII2SiO 5 prepared in different experimental conditions... 

Two-dimensional DQ H MAS-NMR spectra were used to investigate the local structure of a surfactant-templated silicate thin film.498 Silicalite-1 powders (20-1000 nm. crystals) were characterised by 29Si MAS-NMR spectroscopy.499 13C and 29Si solid-state NMR data were used to characterise organic-inorganic mesoporous silica-based materials.500... 

C and 29Si CP/MAS-NMR data were used to characterise the nature of gas-phase deposited y-aminopropylalkoxysilanes on heat-treated Si02.650 29Si solid-state NMR was used to characterise poly(methyloctylsiloxane) (PMOS) deposited on HPLC silica.651,652... 

In addition to the above techniques, inverse gas chromatography, swelling experiments, tensile tests, mechanical analyses, and small-angle neutron scattering have been used to determine the cross-link density of cured networks (240—245). 29Si solid-state nmr and chemical degradation methods have been used to characterize cured networks structurally (246). 2H- and 2H-nmr and spin echo experiments have been used to study the dynamics of cured silicone networks (247—250). 

Figure 3. 29si solid state NMR of Ultradel 1414 and its sol-gel hybrid containing 50 wt-% silica after vacuum drying and annealing at 250 °C for 10 hours. 

Microporous nanoparticles with ordered zeolitic structure such as Ti-Beta are used for incorporation into walls or deposition into pores of mesoporous materials to form the micro/mesoporous composite materials [1-3], Microporous particles need to be small enough to be successfully incorporated in the composite structure. This means that the zeolite synthesis has to be stopped as soon as the particles exhibit ordered zeolitic structure. To study the growth of Ti-Beta particles we used 29Si solid-state and liquid-state NMR spectroscopy combined with x-ray powder diffraction (XRPD) and high-resolution transmission electron microscopy (HRTEM). With these techniques we monitored zeolite formation from the initial precursor gel to the final Ti-Beta product. 

Water intrusion-extrusion isotherms performed at room temperature on hydrophobic pure silica chabazite show that the water-Si-CHA system displays a real spring behavior. However, Pressure/Volume differences are observed between the first and the second cycle indicating that some water molecules interact with the inorganic framework after the first intrusion. 29Si and especially H solid state NMR and powder X-ray diffraction demonstrated the creation of new defect sites upon the intrusion-extrusion of water and the existence of two kinds of water molecules trapped in the super-cage of the Si-CHA a first layer of water strongly hydrogen bonded with the silanols of the framework and a subsequent layer of liquid-like physisorbed water molecules in interaction with the first water layer. 

Here, we have taken advantage of the low silanol content in pure silica LTA and CHA type zeolites synthesized in fluoride medium to get better resolved 29Si and H solid state NMR spectra in the silanol region. This has allowed us to investigate the nature of the silanol groups in zeolites and their interaction with water molecules. 

A tutorial review of 170 solid state NMR has recently been published by Ashbrook and Smith [103]. Although it has been early envisaged that nO solid state NMR can provide useful information on the zeolite framework structure [104, 105], the number of publications employing this nucleus has remained scarce compared to 27A1 or 29Si which is at least in part due to the need for... 

The electrostatically favored cation (Li) and anion (RE) arrangement implies the presence of two different E-, Si- and Li sorts, which has been established by solution and solid-state NMR spectroscopy. The electronic structures of the mixed-valent pnictides 10 and 11 have been simply described as electron-deficient clusters with delocalized framework electrons. Formally the latter consist of two low-valent anediyl moieties RE and eight andiides (RE)2- (E = P, As). The relatively large E-E distances of >4 A exclude the occurrence of localized E-E bonds. However, delocalization of the cluster valence electrons is achieved without Li-Li bonds via Li-mediated multiple bonding. Evidence for this has been seen in the NMR spectra (31P, 7Li, 29Si), which are in accordance with the electron delocalization model (see later discussion). 

Figure 30 Variable-temperature solid-state NMR spectra (relative intensities distorted due to different relaxation rates) (a) 29Si (referenced to Q8M8 (Bruker) (b) 2H (isotropic peak truncated to show hem and crystalline fractions).285 Reprinted with permission from Mueller, C. Schmidt, C. Frey, H. Macromolecules 1996, 29, 3320-3322. 1996 American Chemical Society.

CH3CN (8 -85.1) and 32 CH3CN (8 -84.8) by the solid-state NMR experiments. Furthermore, the solution-state NMR data of 31 and 32 differ significantly from all the other 29Si chemical shifts listed in Table IV. These results are indicative of special structural features of the zwitterions 31 and... 

The samples have also been characterised by means of solid state NMR. 27A1 chemical shifts have been shown to be sensitive to the coordination number and 29Si chemical shifts are strongly influenced by nearest neighbour effects. 

The chemical shift anisotropy of the 29Si nucleus is generally small, and thus unlike in l3C solid-state NMR at high fields, no sideband problems are encountered in MAS spectra of framework silicates. 

A second means of enhancing sensitivity is to increase the concentration of the sample in solution. Thus, 2D-INADEQUATE studies of 29 Si-29 Si correlations on polysilanes at natural 29Si abundance at high concentrations (1 -2 M) was reported12. Sophisticated solid-state NMR studies (see Section V) have also been performed, including two-dimensional... 

In 1997, West and coworkers154 reported the solid-state NMR study of the 29Si chemical shift tensors for a series of disilenes with different substitution at the Si=Si double bond... 

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