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

Ab initio quantum chemistry calculations and comparisons with experimental 17O solid-state nuclear magnetic resonance (NMR) investigations were used to determine the dependence of the 17O quadrupolar coupling constant and asymmetry parameter on the first-coordination-sphere structure around bridging oxygen. The quadrupolar asymmetry parameter was found to be dependent on the Si–O–Si angle, in agreement with previous studies, and independent of the Si–O distance. In contrast, the quadrupolar coupling constant was found to have a strong dependence on Si–O distance as well as Si–O–Si angle. Analytical expressions describing these dependences were proposed and used to develop an approach for relating measured 17O quadrupolar coupling constant and asymmetry parameter values for bridging oxygen to their Si–O–Si angle and average Si–O distance. Examples of this approach were given using 17O NMR results from the crystalline silica polymorphs, coesite, α-quartz, cristobalite, and ferrierite. (Some figures in this article are in colour only in the electronic version) 1