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

Ab initio quantum chemistry calculations and comparisons with experimental O-17 solid-state nuclear magnetic resonance (NMR) investigations were used to determine the dependence of the O-17 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 O-17 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 O-17 NMR results from the crystalline silica polymorphs, coesite, alpha-quartz, cristobalite, and ferrierite.