Water–Halogen Interactions in Chlorine and Bromine Clathrate Hydrates: An Example of Multidirectional Halogen Bonding
Bibliographic record
Abstract
There are unresolved questions in our understanding of the clathrate hydrates with halogen molecule guests. In this work, we describe the synthesis and single crystal X-ray structural determination of cubic structure I (sI) Cl 2, tetragonal structure III (sIII) Br 2, and mixed cubic sI Cl 2 –Br 2 clathrate hydrate phases. Unlike the previous X-ray structural determination of the pure chlorine clathrate hydrate by Pauling and Marsh ( Proc. Nat. Acad. Sci. USA 1952, 38, 112), we report that 32.5% of the clathrate small cages are occupied by Cl 2 molecules. Pure Br 2 produces the unique tetragonal sIII clathrate hydrate whose structure is refined from single-crystal measurements, identifying disordered Br 2 guest positions in cages and giving structural details not previously identified. In mixed sI clathrate hydrate of Cl 2 and Br 2, we observed that Br 2 guests fit into the large sI cages. The introduction of Br 2 in the Cl 2 hydrate lattice causes severe distortions because of strong Br···OH 2 interactions. In these three hydrate structures, based on accepted van der Waals radii, the effective diameters of the clathrate hydrate cages are smaller than the size of the Cl 2 and Br 2 guest molecules. The accommodation of these guests in the cages and the short O···Cl and O···Br contact distances reveal halogen bonding between the water oxygen atoms and the dihalogen guests. The X-ray structural determinations of the length of the Cl–Cl and Br–Br bonds of the Cl 2 and Br 2 guests show significant librational shortening compared to free Cl 2 and Br 2 molecules.
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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 | 0.001 |
| 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".