29Si NMR of Inorganic Solids

Abstract

Since the first systematic study of silicates and aluminosilicates by high-resolution solid-state 29Si NMR was published in 1980 [1], the application of this method has grown rapidly and is fast becoming a powerful tool in the structural characterization of a wide range of silicates and other silicon-containing materials. The development is closely related to the great progress made in the last decade in the instrumentation, techniques and methods for the registration and evaluation of the 29Si NMR spectra and their structural interpretation. Nowadays, high magnetic field strengths and a wide selection of experimental techniques are available by modern solid-state NMR spectrometers. Since 29Si is a spin 1/2 nucleus, magic angle spinning (MAS) yields simple spectra with complete averaging of the chemical-shift anisotropy and is, therefore, the most important technique for the measurement of highly resolved 29Si NMR spectra of microcrystalline or amorphous solids. In proton containing samples, line broadening due to dipolar 29Si-1H interactions can be removed by high power proton decoupling, and cross-polarization (CP) may be used for signal enhancement and the detection of protons in close proximity to the silicon atom, e.g. in SiOH groupings. In addition, 2D 29Si MAS NMR techniques such as COSY and INADEQUATE have recently been applied to study three-dimensional framework connectivities.