Assessing distortion of the AF 6 − (A=As, Sb) octahedra in solid hexafluorometallates(V) via NMR spectroscopy
Bibliographic record
Abstract
Arsenic and antimony hexafluoride salts have played an important role in the history of both solution and solid-state NMR spectroscopy. Here, solid polycrystalline KAsF 6 and KSbF 6 have been studied via high-resolution variable temperature 19 F, 75 As, 121 Sb, and 123 Sb solid-state NMR spectroscopy at high magnetic field (B 0 = 21.14 T). Both KAsF 6 and KSbF 6 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 ( 75 As) values for KAsF 6 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 ( 75 As) = 0 Hz, consistent with the crystal symmetry at the arsenic nucleus in this phase. In contrast, C Q values for 121 Sb and 123 Sb in the cubic phase of KSbF 6 are nonzero. E.g., at 293 K, C Q ( 121 Sb) = 6.42 ± 0.10 MHz, and C Q ( 123 Sb) = 8.22 ± 0.10 MHz. In the higher temperature tetragonal phase (343 K) of KSbF 6 , 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 1 J( 75 As, 19 F) = −926 ± 10 Hz (293 K) and −926 ± 3 Hz (348 K), and 1 J( 121 Sb, 19 F) = −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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".