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.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 | 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 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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 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".