Dependence of bridging oxygen 17Oquadrupolar coupling parameters on Si–O distance and Si–O–Si angle

Abstract

Ab initio quantum chemistry calculations and comparisons withexperimental 17O solid-state nuclear magneticresonance (NMR) investigations were used to determine the dependenceof the 17O quadrupolar coupling constantand asymmetry parameter on the first-coordination-sphere structurearound bridging oxygen. The quadrupolar asymmetry parameter was foundto be dependent on the Si–O–Si angle, in agreement withprevious studies, and independent of the Si–O distance. Incontrast, the quadrupolar coupling constant was found to have astrong dependence on Si–O distance as well asSi–O–Si angle. Analytical expressions describing thesedependences were proposed and used to develop an approach forrelating measured 17O quadrupolar coupling constantand asymmetry parameter values for bridging oxygen to theirSi–O–Si angle and average Si–O distance. Examplesof this approach were given using 17O NMR results from thecrystalline silica polymorphs, coesite, α-quartz, cristobalite, andferrierite.