文摘
High-field, ambient-temperature (AT) 17O MAS NMR spectra of the tetraoxoanion IO4鈥?/sup> in NaIO4 and KIO4 exhibit unusual line-shape features for the central transition (CT), which so far have not been observed in any second-order broadened line shape for the CT of a quadrupolar nucleus. These features are caused by an unusually large isotropic 1J(17O-127I) spin coupling (鈭?00 Hz) and appear like 鈥渢eeth-on-a-saw鈥? This study reports interesting results obtained from optimized fitting of the spectra using our recently described XSTARS software. The results include determination of a positive sign for 1J(17O-127I) (= +500 Hz), an unusual observation in solid-state NMR. NMR crystallography shows a very precise correlation between extraordinary small changes for the 17O asymmetry parameter (畏Q) and changes for a tetrahedral O鈥揑鈥揙 angle upon distortion from an ideal tetrahedron. Similarly, the spectral analysis shows that the NMR crystallography requires the principal axes Vzz(17O) and 未zz(17O) of the PAS for these tensors are both almost along the I鈥揙 bond. All the experimental data are in excellent agreement with our ADF and CASTEP calculations.