An 17O NMR Investigation of Crystalline Sodium Metasilicate:  Implications for the Determination of Local Structure in Alkali Silicates

Crystalline sodium metasilicate, Na2SiO3, has been investigated by 29Si, 23Na, and 17O MAS NMR spectroscopy. The 17O quadrupolar coupling parameters have been measured for the bridging oxygen (BO) and nonbridging oxygen (NBO) sites. Ab initio calculations have also been performed for clusters modeling these oxygen sites, as well as other sites in crystalline silicates of known structure. On the bases of ab initio calculations, parametrized equations are discussed which describe trends in the BO 17O quadrupolar coupling parameters. The agreement between these parametrized equations and reported values for a variety of crystalline environments is shown to be quite good. The ab initio calculated NBO 17O quadrupolar coupling parameters are also in agreement with measured results for Na2SiO3 and analogous crystalline alkali silicates such as α-Na2Si2O5 and Li2Si2O5.