On 29Si NMR relaxation as a structural criterion for studying paramagnetic supermicroporous silica-based materials: silica-based materials incorporating Mn2+ ions into the silica matrix of SiO2-Al2O3-MnO.

Supermicroporous paramagnetic materials SiO(2)-Al(2)O(3)-MnO and SiO(2)-MnO with different manganese concentrations have been probed by solid-state (29)Si NMR and magnetic susceptibility measurements. The (29)Si T(1) and T(2) experiments, performed in static and spinning samples, have resulted in determination of electron relaxation times, providing, in turn, quantitative interpretations of (29)Si T(1) times in terms of distances Mn-Si. The NMR relaxation data have revealed (29)Si T(1) time distributions, which are close to Gaussian and observed as different T(1) values obtained in MAS NMR experiments for isotropic (29)Si resonances and their sidebands.

Structure of a paramagnetic supermicroporous silica-based material via a multinuclear solid-state NMR monitoring.

The paramagnetic Si/Al material doped with 19.8% (weight) of Mn2+ has been characterized by the 1H, 13C, 27Al, 29Si MAS NMR spectra and the 1H, 29Si T1MAS relaxation measurements as a gel dried at 130 degrees C and as samples calcined at 504, 540 and 650 degrees C. It has been demonstrated that in spite of strong paramagnetic effects, NMR monitoring in combination with 29Si T1 relaxation experiments can be successful for structural descriptions of porous materials.

29Si spin-lattice NMR relaxation in microporous silica-based materials with high Mn2+ concentrations.

The 29Si T1 time measurements have been performed under magic angle spinning for supermicroporous Si/Mn materials 1-6 containing Mn2+ in concentrations of 0 (1), 1.2 (2), 2.5 (3), 3.

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 29Si, 27Al MAS NMR spectra and 29Si T1 measurements. The single-pulse 29Si and 27Al 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 29Si and 27Al nuclei observed in the single-pulse NMR spectra have been assigned to nuclei remote from paramagnetic centers.

New families of supermicroporous metal oxides: the link between zeolites and mesoporous materials.

Sol-gel hydrolysis reactions in propanol of two or more metal acetates or alkoxides in n-alkylamines have been found to yield porous mixed oxides with the presence of pores largely in the 10-20 A region.