Relationships between bridging oxygen [formula omitted]O quadrupolar coupling parameters and structure in germanates

Abstract

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.