High-Field O-17 MAS NMR Reveals (1)J(O-17-I-127) with its Sign and the NMR Crystallography of the Scheelite Structures for NaIO4 and KIO4

摘要

High-field, ambient-temperature (AT) O-17 MAS NMR spectra of the tetraoxoanion IO4 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 (1)J(O-17-I-127) spin coupling (similar to 500 Hz) and appear like teeth-on-a-saw. 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 (1)J(O-17-I-127) (= +500 Hz), an unusual observation in solid-state NMR. NMR crystallography shows a very precise correlation between extraordinary small changes for the O-17 asymmetry parameter (eta(Q)) and changes for a tetrahedral O-I-O angle upon distortion from an ideal tetrahedron. Similarly, the spectral analysis shows that the NMR crystallography requires the principal axes V-zz(O-17) and delta(zz)(O-17) of the PAS for these tensors are both almost along the I-O bond. All the experimental data are in excellent agreement with our ADF and CASTEP calculations.