Halogen Bond Strength in Solids Quantified via Zeeman-Perturbed Nuclear Quadrupole Resonance Spectroscopy
Bibliographic record
Abstract
Proton NMR is a ubiquitous and valuable probe of hydrogen bonds. Conversely, 127 I NMR of strong halogen bond (XB) donors is hopeless due to quadrupolar coupling constants ( C Q ) on the order of GHz. We report here an innovative implementation of Zeeman-perturbed nuclear quadrupole resonance (Zp-NQR) spectroscopy, employing adjustable magnetic fields on the order of mT, which renders possible the acquisition and analysis of spectra of 127 I and 79 Br nuclei subject to quadrupolar couplings of up to 2.3 GHz in solid powders. This approach is demonstrated on three series of halogen-bonded cocrystals based on so-called “iconic” strong XB donors p -diiodotetrafluorobenzene, sym -trifluorotriiodobenzene, and p -dibromotetrafluorobenzene (27 compounds). Analysis of the spectra using a diagonalization of the Zeeman-quadrupolar Hamiltonian provides C Q values and quadrupolar asymmetry parameters, thereby overcoming various limitations encountered in pure NMR and pure NQR. Inspection of the data reveals strong correlations with geometrical and structural features of the halogen bond, including its length. Dispersion-corrected zeroth-order regular approximation relativistic DFT computations of the interaction energies of the XB donor are strongly correlated with experimental and computed values of C Q ( 127 I) and C Q ( 79 Br). It is concluded that the electric field gradient at the XB donor site is a useful metric for quantifying XB strength in solids. The XB interaction energies range from ∼5 to 10 kcal mol –1 for the systems studied herein. The Zp-NQR approach is amenable to widespread application to diverse problems in the chemical and materials sciences related to energy materials, crystal engineering, and many systems comprising strongly quadrupolar isotopes.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".