Structural characterization of the new porous sodium silicate Mu-11 by Si-29 and Na-23 solid-state NMR

A variety of solid-state NMR techniques were applied in order to assign res onances in the Si-29 and Na-23 NMR spectra of a new crystalline silicate to crystallographically distinct silicon and sodium sites, respectively. Mu-1 1 is a zeolite-like material with a 1D channel system occupied by water and sodium cations whose framework contains both bridging and non-bridging oxy gens. The observed Si-29 isotropic chemical shifts did not allow a direct a ssignment. A preliminary assignment based on the electronegativities calcul ated for the four ligands around each silicon was supported by correlations between the extent of the distortion from an ideal tetrahedron and the mea sured chemical shift anisotropy for the different Si sites. H-1-Si-29 cross polarization experiments confirmed the assignments. The two crystallograph ically different sodium atoms were resolved by Na-23 3Q-MAS NMR, and an ass ignment for these two sites is proposed.