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摘要
Arsenic and antimony hexafluoride salts have played an important role in the history of both solution and solid-state NMR spectroscopy. Here, solid polycrystalline KAsF6 and KSbF6 have been studied via high-resolution variable temperature F-19, As-75, Sb-121, and Sb-123 solid-state NMR spectroscopy at high magnetic field (B-0 = 21.14 T). Both KAsF6 and KSbF6 undergo solid-solid phase transitions at approximately 375 and 301 K, respectively. We use variable temperature NMR experiments to explore the effects of crystal structure changes on NMR parameters. C-Q(As-75) values for KAsF6 at 293, 323, and 348 K are -2.87 +/- 0.05 MHz, -2.58 +/- 0.05 MHz, and -2.30 +/- 0.05 MHz, respectively, the sign determined via DFT calculations. In the higher temperature cubic phase, C-Q(As-75) = 0 Hz, consistent with the crystal symmetry at the arsenic nucleus in this phase. In contrast, C-Q values for Sb-121 and Sb-123 in the cubic phase of KSbF6 are nonzero. E.g., at 293 K, C-Q(Sb-121) = 6.42 +/- 0.10 MHz, and C-Q(Sb-123) = 8.22 +/- 0.10 MHz. In the higher temperature tetragonal phase (343 K) of KSbF6, these values are 3.11 +/- 0.20 MHz and 4.06 +/- 0.20 MHz, respectively. CASTEP calculations performed on the cubic and tetragonal structures support this trend. Isotropic indirect spin-spin coupling constants are 1J(As-75, F-19) = -926 +/- 10 Hz (293 K) and -926 +/- 3 Hz (348 K), and 1J(Sb-121, F-19) = -1884 +/- 3 Hz (293 K), and -1889 +/- 3 Hz (343 K). Arsenic-75 and antimony-121,123 chemical shift values show little variation over the studied temperature ranges.
- 出版日期2015-9
