Improved baseline in 29Si NMR spectra of water glasses

It is shown by experiments that replacing one‐pulse sequence by RIDE (ring down elimination) pulse sequence may dramatically improve the baseline of ²⁹Si NMR spectra and eliminate the signal from the probe. Copyright © 2013 John Wiley & Sons, Ltd.     

13C, 15N and 29Si NMR spectra of triazasilatranes

¹³C, ¹⁵N and ²⁹Si chemical shifts and ²⁹Si¹H, ²⁹Si¹³C and ²⁹Si¹⁵N coupling constants as well as SiH bond stretching frequencies in the triazasilatranes (I) (2,5,8,9-tetraaza-1-silatricyclo[3.3.3.0^1,5] undecanes) and model compounds, tris(alkylamino)silanes with R_Si = H, Me, CH₂CH (Vi) and C₆H₅ (Ph) were measured. A stronger intramolecular N → Si bonding was revealed in I compared with their oxygen analogues, silatranes (II). This was assumed to be caused by the higher polarity of the equatorial SiX bonds in I (X = NH) in comparison with II (X = O).     

1H, 13C and 29Si NMR spectra of allylic trimethylsilanes

Chemical shift and scalar coupling constant data have been obtained for the ¹H, ¹³C and ²⁹Si nuclei in allyl, methally, cis- and trans-crotyl, cis-2-methyl-2-butenyl and 3-methyl-2-butenyl derivatives of trimethylsilane.     

29Si and 27Al MAS NMR spectra of mullites from different kaolinites

Mullites synthesized from four kaolinites with different random defect densities have been studied by 27Al and 29Si magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) and X-ray diffraction (XRD). All these mullites show the same XRD pattern. However, 29Si and 27Al MAS NMR spectra reveal that the mullites derived from kaolinites with high defect densities, have a sillimanite-type Al/Si ordering scheme and are low in silica, whereas those mullites derived from kaolinites with low defect densities, consist of both sillimanite- and mullite-type Al/Si ordering schemes and are rich in silica.     

29Si NMR spectra of trimethylsilylated cyclic acyloins and ketones. 29Si chemical shifts as a measure of ring size

²⁹Si chemical shifts are reported for nine 1,2-bis(trimethylsiloxy)cycloalkenes and four 1-trimethylsiloxycycloalkenes, (Me₃SiO)_xC_nH_2n–2–x (x=1, 2). For cycloalkene derivatives with n?8 the silicon shift exhibits a strong dependence on the ring size, although the silicon is exocyclic and is separated by two bonds from the olefinic carbon atom. The dependence can be exploited for ring size determination of cyclic ketones after trimethylsilylation.     

29Si NMR spectroscopy of cyclosiloxanes

Journal of Structural Chemistry -     

1H, 13C,and 29Si NMR spectra of 1-methylazasilatrane

Considerable shielding of the ¹H and ²⁹Si nuclei due to transannular nitrogen-silicon coupling, which is expressed more clearly than in the case of silatranes, was established on the basis of ¹H, ¹³C, and ²⁹Si NMR data for the methylsilyl group in 1-methyl-2,5,8,9-tetraaza-1-silatricyclo[3.3.3.0^1,5]undecane (1-methylazasilatrane) and a comparison of these data with the data for the methyl[tris(dimethylamino)]silane model. It is shown that the change in the hybridization of the silicon atom associated with the increase in its coordination number is not only reflected in the chemical shifts but also leads to an increase in ¹J_CH and ²J_SiH.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1063–1064, August, 1977.     

29Si NMR Spektroskopie von Cyclopentasilanen

The structure and ²⁹Si chemical shifts of the halodimethylsilylnonamethylcyclopentasilanes Si₅Me₉SiMe₂X (1–4) and the halononamethylcyclopentasilanes Si₅Me₉X (5–8) (X = F, Cl, Br, I) have been assigned using ¹J(SiSi) and ²J(SiSi) coupling constants derived from ²⁹Si-INADEQUATE and ²⁹Si-INEPT—INADEQUATE NMR spectra. The compounds exhibit good correlation between chemical shift, ¹J(SiSi) and Pauling electronegativities.     

Effect of molecular oxygen on the variable-temperature 29Si MAS NMR spectra of zeolite-sorbate complexes

Structure determinations of siliceous zeolite-sorbate host-guest complexes by solid-state NMR require highly resolved 29Si MAS NMR spectra. As the temperature is lowered, the 29Si MAS NMR spectra of many zeolite-sorbate complexes become broadened such that the resolution of the individual 29Si peaks is lost, limiting the application of solid-state NMR for structure determination. It is shown that the 29Si peak widths are related to the 29Si T2 relaxation times and that the source of the 29Si relaxation and the line broadening is paramagnetic molecular oxygen in the channels of the zeolite. Removal of the oxygen by purging the sample with nitrogen gas leads to a dramatic increase in the resolution of the 29Si MAS NMR spectrum of the p-dibromobenzene/ZSM-5 complex. An analysis of the individual 29Si T1 relaxation times reveals that the oxygen molecules are localized mainly in the zigzag channels of ZSM-5, suggesting that the p-dibromobenzene molecules are located in the channel intersections.     

29Si NMR investigations on oligosilane dendrimers

Starting with the high functionalized trisilane SiClMe(SiCl₂Me)₂ and tetrasilane SiMe(SiCl₂Me)₃ several octa- and decasilane dendrimers containing directly neighboured branchings were prepared. In these compounds the ²⁹Si NMR chemical shifts of the different silyl groups are shifted towards lower field compared with those of analogous groups in tetra- or hexasilanes. This observation is a helpful tool for the characterization of further dendritic oligomers by ²⁹Si NMR. Received: 3 June 1996 / Revised: 3 July 1996 / Accepted: 9 July 1996     

29Si NMR investigations on oligosilane dendrimers

Starting with the high functionalized trisilane SiClMe(SiCl₂Me)₂ and tetrasilane SiMe(SiCl₂Me)₃ several octa- and decasilane dendrimers containing directly neighboured branchings were prepared. In these compounds the ²⁹Si NMR chemical shifts of the different silyl groups are shifted towards lower field compared with those of analogous groups in tetra- or hexasilanes. This observation is a helpful tool for the characterization of further dendritic oligomers by ²⁹Si NMR. Received: 3 June 1996 / Revised: 3 July 1996 / Accepted: 9 July 1996     

The fine structure of high-resolution solid state 29Si NMR spectra of zeolites X and Y

Examination of ²⁹Si magic-angle-spinning NMR spectra of zeolites with the faujasite structure reveals that the characteristic pattern of linewidths and chemical shifts is due to effects in the first coordination shell of silicon.     

Structural study of arylsilanes using 29Si NMR

²⁹Si NMR data (σ and ¹H, ²⁹Si coupling constants) of a series of arylsilanes were studied in relation to their molecular structure. It is shown that silicon chemical shift variation is too weak to allow empirical attribution. In contrast, ²⁹Si, ¹H coupling constants across the aromatic ring, especially the ³J, allow structural assignment. Generally, SPT experiments are sufficient to obtain these values. However, full attribution of polysilylated derivatives sometimes needs other experiments to identify all the silicons. A 2D J-resolved INEPT experiment is described and has proven to be an efficient method for ²⁹Si NMR signal identification. The usefulness of this approach is demonstrated by the complete analysis of all the ²⁹Si lines in a trisilyl derivative. An easy-to-use INEPT decoupled-type sequence is also proposed for a rapid characterization of polysilylated derivatives or mixture of isomers.     

29Si NMR studies of zeolite precursor solutions

Solution 29Si NMR spectroscopy results of zeolite precursor solutions of composition 1 SiO2:4 C2H5OH:0.36/n R+n[OH-]n:20 H2O are reported. This work employs isotopically enriched 29Si materials to aid in spectral interpretation. Using both 1D and 2D methods, spectra of solutions containing tetrapropylammonium hydroxide are wholly consistent with the existing silicate chemistry literature and indicate that the majority of the species are high-symmetry silicate clusters previously observed in aqueous solutions. The results are inconsistent with the nanoblock or nanoslab model proposed by Kirschhock and co-workers. Mixtures containing the 4,4'-trimethylene-bis(1,1'-dimethylpiperidinium) dihydroxide cation were also studied. These mixtures have similar speciation to the TPA solutions, although the relative populations of the species are different. Preliminary variable temperature 29Si NMR of these mixtures shows that the exchange properties of the high-symmetry silicate species, most notably the tetrahedral tetramer, depend on the organocation identity.     

29Si chemical shift anisotropies in calcium silicates from high-field 29Si MAS NMR spectroscopy

29Si chemical shift anisotropy (CSA) data have been determined from (29)Si MAS NMR spectra recorded at 14.1 T for a number of synthetic calcium silicates and calcium silicate hydrates. These are beta- and gamma-Ca(2)SiO(4), Ca(3)SiO(4)Cl(2), alpha-dicalcium silicate hydrate (alpha-Ca(2)(SiO(3)OH)OH), rankinite (Ca(3)Si(2)O(7)), cuspidine (Ca(4)Si(2)O(7)F(2)), wollastonite (beta-Ca(3)Si(3)O(9)), pseudowollastonite (alpha-Ca(3)Si(3)O(9)), scawtite (Ca(7)(Si(6)O(18))CO(3).2H(2)O), hillebrandite (Ca(2)SiO(3)(OH)(2)), and xonotlite (Ca(6)Si(6)O(17)(OH)(2)). The (29)Si MAS NMR spectra of rankinite and wollastonite clearly resolve manifolds of spinning sidebands from two and three Si sites, respectively, allowing the CSA parameters to be obtained with high precision for each site. For the (29)Si Q(1) sites in rankinite and cuspidine, the CSA asymmetry parameters (eta(sigma) approximately 0.6) contrast the general expectation that sorosilicates should possess small eta(sigma) values as a result of the nearly axially symmetric environments of the SiO(4) tetrahedra. The (29)Si CSA parameters provide an improved insight into the electronic and geometric environments for the SiO(4) tetrahedra as compared to the values solely for the isotropic chemical shift. It is shown that the shift anisotropy (delta(sigma)) and the CSA asymmetry parameter (eta(sigma)) allow a clear distinction of the different types of condensation of SiO(4) tetrahedra in calcium silicates. This relationship may in general be valid for neso-, soro-, and inosilicates. The CSA data determined in this work may form a valuable basis for (29)Si MAS NMR studies of the structures for tobermorites and calcium silicate hydrate phases resulting from hydration of Portland cements.     

Kinetics of interaction of 3-aminopropyltriethoxysilane with silica gel using elemental analysis and 29Si NMR spectra

 Three silica gel sample systems, modified with 3-amino-propyltriethoxy silane (APTS), were prepared by sequentially sampling the reaction mixture at various time intervals. The concentrations of 3-aminopropylsilyl groups (APS) bound on the silica surface were determined by elemental analysis. For the same sample systems, ²⁹Si NMR intensities of an (–O)₄Si species belonging only to the silica gel particles and corrected by a cross-polarization correction factor were also measured. Both the APS-concentrations and the correc-ted ²⁹Si NMR intensities depended upon reaction time, reflecting the rate of the APTS–silica gel reaction. Kinetic analysis of these data was made by use of the Gauss–Newton method, and the overall reaction was found to consist of three reaction processes (an initial fast reaction, a slower second reaction and a much slower third reaction). In particular, the conversion of (–O)₃SiOH to (–O)₄Si is predominant in the second reaction process and the pore size of a silica gel particle affects the reaction mechanism. Received: 1 November 1996 Accepted: 24 January 1997     

29Si NMR study of configurations of cyclo-linear polymethylsiloxanes

A technique based on the²⁹Si NMR spectra for analyzing the spatial structure of cyclolinear polymethylsiloxanes has been developed. The role of certain factors influencing the formation of the spatial structure of the chains during the preparation of these polymers has been studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1460–1466, August, 1993.     

29Si NMR Shielding Tensors in Triphenylsilanes – 29Si Solid State NMR Experiments and DFT‐IGLO Calculations

²⁹Si NMR shielding tensors of a series of triphenylsilanes Ph₃SiR with R = Ph, Me, F, Cl, Br, OH, OMe, SH, NH₂, SiPh₃, C≡CPh were determined from ²⁹Si CP/MAS spectra recorded at low spinning rates. In addition the principal components of the shielding tensor were calculated employing the DFT‐IGLO method. For most silanes experimental and calculated values are in good accordance. Larger differences were observed for systems with hydrogen bridge forming substituents and the halides bromide and chloride. In some of the spectra the shielding information interfered with residual dipolar couplings. The different contributions of the various substituents to the principal components of the shielding tensor and the orientation of the tensor within the molecules are discussed and compared for the compounds under investigation.