Relationships between bridging oxygen O quadrupolar coupling parameters and structure in germanates

We have performed ab initio calculations on the model cluster (OH) ₃Ge–O–Ge(OH) ₃ in order to refine the relationships between 17 O quadrupolar coupling parameters and the local structure around the bridging oxygen. From these calculations the trend in the bridging oxygen 17 O quadrupolar coupling constant, C _q, and asymmetry parameter, η _q, with changing Ge–O–Ge angle was found to be similar to previously established trends in silicate clusters with the overall C _q values being systematically increased in magnitude by approximately 3 MHz. Such a shift can be attributed to differences in cation–oxygen distances as well as coordinating cation electronegativity. In addition, we also investigated the effect of changing intratetrahedron bond angles over a range that has been suggested to exist in germanate systems. While such variations in intratetrahedron bond angles lead to a small variation in C _q, η _q remains relatively unaffected. In such cases, η _q can still be a reliable probe of Ge–O–Ge angle while C _q could serve as a probe of tetrahedron distortions.