Relationships between bridging oxygen 17O 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 17O quadrupolar coupling parameters and the local structure around the bridging oxygen. From these calculations the trend in the bridging oxygen 17O quadrupolar coupling constant, Cq, and asymmetry parameter, ηq, with changing Ge–O–Ge angle was found to be similar to previously established trends in silicate clusters with the overall Cq 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 Cq, ηq remains relatively unaffected. In such cases, ηq can still be a reliable probe of Ge–O–Ge angle while Cq could serve as a probe of tetrahedron distortions.