One- and two-dimensional high-resolution solid-state NMR studies of zeolite lattice structures

Structure of Framework Aluminum Lewis Sites and Perturbed Aluminum Atoms in Zeolites as Determined by 27Al{1H} REDOR (3Q) MAS NMR Spectroscopy and DFT/Molecular Mechanics

“…Note that the analysis of (SiO) 3 AlOH by 29 Si MAS NMR spectroscopy is significantly limited by the only 25 % difference in the intensity between the Si(3 Si,1 Al) and Si(3 Si,1 AlOH) NMR signals. [12] Also, the application of 27 Al single-pulse MAS NMR spectroscopy considerably underestimates the concentration of (SiO) 3 AlOH groups owing to the overlap of their resonance with that of the framework Al atoms.…”

Geminal2J(29Si‐O‐29Si) couplings in oligosiloxanes and their relation to direct1J(29Si‐13C) couplings

“…Methoxysiloxanes necessary for syntheses were prepared in similar way as shown in Scheme 2. 13 C labeled hexamethyldisiloxane (2b) was prepared by alkylation of 1,3-dichloro-1,1,3,3-tertramethyldisiloxane with 13 C-methylmagnesium iodide.…”

“…channels, two of them fitted with waveform generators. The operating frequencies were 499.9, 125.7 and 99.3 MHz for 1 H, 13 Magnitudes of coupling constants were deduced from 1D 13 C spectra (acquisition time 2.6 s, spectral width 2.2 kHz, zero filling to double the number of data points and accumulation of 512 transients) and 1D 29 Si NMR spectra (measured either by INEPT [30,31] or by single pulse with gated proton decoupling) with acquisition time 12 s, spectral width depending on substrate, zero filling to double the number of data points and accumulation of 1024 transients), within experimental error (estimated at ±0.08 Hz) both methods gave the same results in all cases. Though the signs of these couplings were not determined here, the couplings are taken as negative in accordance to general observations.…”

“…The desired coupling can be extracted from 13 C satellite spectra (originating from 13 C- 29 Si-O- 29 Si isotopomer with natural abundance 9.6 × 10 −3 %) in which the 1 J( 29 Si-13 C) coupling removes the degeneracy. In view of the low abundance it is more practical to use (relatively easy and inexpensive to prepare) 13 C enriched sample.…”

“…The desired coupling can be extracted from 13 C satellite spectra (originating from 13 C- 29 Si-O- 29 Si isotopomer with natural abundance 9.6 × 10 −3 %) in which the 1 J( 29 Si-13 C) coupling removes the degeneracy. In view of the low abundance it is more practical to use (relatively easy and inexpensive to prepare) 13 C enriched sample. The simplest route (alkylation of 1,3-dichloro-1,1,3,3-tetramethyldisiloxane) yields, however, the symmetrical product 2b containing 13 C-Si-O-Si- 13 C moiety with natural 0.16% abundance of 13 C- 29 Si-O- 29 Si-13 C isotopomer.…”