The first chromium-53 solid-state nuclear magnetic resonance spectra of diamagnetic chromium(0) and chromium(VI) compounds
Bibliographic record
Abstract
Chromium-53 is a spin-3/2 nucleus with a relatively small magnetic moment, low natural abundance, and large quadrupole moment. These properties have severely hampered the development of 53Cr NMR, especially in the solid state. In this Communication, the first 53Cr solid-state NMR spectra of prototypal diamagnetic chromium(0) and chromium(VI) compounds are presented. Specifically, analyses of 53Cr NMR spectra of solid hexacarbonylchromium(0), caesium chromate(VI), and potassium chromate(VI) have allowed for the determination of 53Cr quadrupolar coupling parameters and the first chromium chemical shift (CS) tensors. This work demonstrates the potential of 53Cr solid-state NMR, in particular the extreme sensitivity of the 53Cr quadrupolar coupling constant to the local chromium environment. Comparisons are made to known 53Cr NMR parameters available from solution studies, and to the 95Mo solid-state NMR parameters of analogous molybdenum compounds. The influence of crystal symmetry present in isomorphic Cr(CO)6 and Mo(CO)6 is strongly reflected in the magnitudes of the metal nuclei CS tensors and in their orientation with respect to their corresponding electric field gradient tensors.
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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 | 0.001 |
| 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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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".