SI-29 MAS NMR-SPECTROSCOPY OF TECTOZINCOSILICATES

Si-29 MAS NMR spectroscopic data from dense (Na2ZnSiO4, Na(2)ZnSi2O6, K2ZnSi4O10) and microporous (VPI-7, VPI-9) tectozincosilicates are presented. These results allow for the first time the assignment of the chemical shift ranges for silicon environments (Si:nSi,4-nZn; n = 0-4) in tectozincosilicates. A comparison between the chemical shift ranges of tectozincosilicates and tectoaluminosilicates (zeolites) is provided, and the differences are rationalized in terms of the Zn-O-Si bonding. Unlike aluminosilicates, a high degree of Zn, Si ordering is observed in all the materials investigated. Predictions of structural details for the tectozincosilicates VPI-7 and VPI-9 are made, and several general aspects of the crystal chemistry of tectozincosilicates are discussed in view of the NMR data.