Solid-state NMR spectra of paramagnetic silica-based materials:: observation of 29Si and 27Al nuclei in the first coordination spheres of manganese ions

Some silica-based solids, prepared by the sol/gel method in the presence of high Mn2+ concentrations, have been characterized by the Si-29, Al-27 MAS NMR spectra and Si-21 T-1 measurements. The single pulse Si-29 and Al-27 MAS NMR spectra have shown broad spinning sideband patterns that are interpreted in terms of anisotropic bulky magnetic susceptibility (BMS) and dipole-field effects. In the absence of paramagnetic isotropic shifts, the Si-21 and Al-27 nuclei observed in the single-pulse NMR spectra have been assigned to nuclei remote from paramagnetic centers. It has been demonstrated that the Si-21 and Al-27 nuclei, which are in the vicinity of the manganese ions, can be detected by the Hahn-echo MAS NMR experiments at different carrier frequencies. Copyright (c) 2006 John Wiley & Sons, Ltd.