A Pressure Induced Structural Dichotomy in Isostructural Bis-1,2,3-thiaselenazolyl Radical Dimers
Bibliographic record
Abstract
The pressure dependence of the crystal and molecular structure of the bis-1,2,3-thiaselenazolyl radical dimer [ 1b ] 2 has been investigated over the range 0–11 GPa by powder diffraction methods using synchrotron radiation and diamond anvil cell techniques. At ambient pressure, the dimer consists of a pair of radicals linked by a hypervalent 4-center 6-electron S---Se–Se---S σ-bond in an essentially coplanar arrangement. The dimers are packed in cross-braced slipped π-stack arrays running along the x -direction of the monoclinic (space group P 2 1 / c ) unit cell. Pressurization to 11 GPa causes the unit cell dimensions a and c to undergo a slow but uniform compression, while the b -axis is slightly elongated. There is virtually no change in the molecular structure or in the slipped π-stack crystal architecture. This behavior is in marked contrast to that of the isostructural radical dimer [ 1a ] 2, where the basal fluorine is replaced by hydrogen. Pressurization of this latter material induces a phase change near 4–5 GPa, characterized by a sharp contraction in a and c, and a correspondingly large increase in b . At the molecular level, the transition is associated with a buckling of the σ-bonded dimer to a more conventional π-bonded arrangement. Geometry optimized DFT band structure calculations on [ 1b ] 2 replicate the observed structural changes and indicate that compression widens both the valence and conduction bands but does not induce band gap closure until >13 GPa. This result is consistent with the measured thermal activation energy for conduction E act, which indicates that a metallic state requires pressures > 10 GPa.
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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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".