Prospects for <sup>207</sup>Pb solid-state NMR studies of lead tetrel bonds
Bibliographic record
Abstract
The feasibility and value of 207 Pb solid-state NMR experiments on compounds featuring lead tetrel bonds is explored. Although the definition remains to be formalized, lead tetrel bonds may be qualitatively described as existing when there is evidence of a net attractive interaction between an electrophilic region associated with lead in a molecular entity and a nucleophilic region in another, or the same, molecular entity. Unambiguous identification of lead tetrel bonds can be challenging due to the hypervalent tendency of lead. We report here a series of 207 Pb solid-state NMR experiments on five metal–organic frameworks featuring lead coordinated to hydrazone-based ligands. Such frameworks may be held together in part by lead tetrel bonds. The acquisition of 207 Pb solid-state NMR spectra for such materials is feasible and is readily accomplished using a combination of magic-angle spinning and Carr–Purcell–Meiboom–Gill methods in moderate to low applied magnetic fields. The lead centres are characterized by 207 Pb isotropic chemical shifts ranging from −426 to −2591 ppm and chemical shift tensor spans ranging from 910 to 2681 ppm. Careful inspection of the structures of the compounds and the literature 207 Pb NMR data may suggest that a tetrel bond to lead results in chemical shift parameters which are intermediate between those which are characteristic of holodirected and hemidirected lead coordination geometries. Challenges associated with DFT computations of the 207 Pb NMR parameters are discussed. In summary, the 207 Pb data for the compounds studied herein show a marked response to the presence of non-coordinating electron-rich moieties in close contact with the electrophilic surface of formally hemidirectionally coordinated lead compounds.
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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 | 0.002 | 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 | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 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".