Hysteretic Spin Crossover between a Bisdithiazolyl Radical and Its Hypervalent σ-Dimer
Why this work is in the frame
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Bibliographic record
Abstract
The bisdithiazolyl radical 1a is dimorphic, existing in two distinct molecular and crystal modifications. The α-phase crystallizes in the tetragonal space group P4̅2(1)m and consists of π-stacked radicals, tightly clustered about 4̅ points and running parallel to c. The β-phase belongs to the monoclinic space group P2(1)/c and, at ambient temperature and pressure, is composed of π-stacked dimers in which the radicals are linked laterally by hypervalent four-center six-electron S···S-S···S σ-bonds. Variable-temperature magnetic susceptibility χ measurements confirm that α-1a behaves as a Curie-Weiss paramagnet; the low-temperature variations in χ can be modeled in terms of a 1D Heisenberg chain of weakly coupled AFM S = (1)/(2) centers. The dimeric phase β-1a is essentially diamagnetic up to 380 K. Above this temperature there is a sharp hysteretic (T↑= 380 K, T↓ = 375 K) increase in χ and χT. Powder X-ray diffraction analysis of β-1a at 393 K has established that the phase transition corresponds to a dimer-to-radical conversion in which the hypervalent S···S-S···S σ-bond is cleaved. Variable-temperature and -pressure conductivity measurements indicate that α-1a behaves as a Mott insulator, but the ambient-temperature conductivity σ(RT) increases from near 10(-7) S cm(-1) at 0.5 GPa to near 10(-4) S cm(-1) at 5 GPa. The value of σ(RT) for β-1a (near 10(-4) S cm(-1) at 0.5 GPa) initially decreases with pressure as the phase change takes place, but beyond 1.5 GPa this trend reverses, and σ(RT) increases in a manner which parallels the behavior of α-1a. These changes in conductivity of β-1a are interpreted in terms of a pressure-induced dimer-to-radical phase change. High-pressure, ambient-temperature powder diffraction analysis of β-1a confirms such a transition between 0.65 and 0.98 GPa and establishes that the structural change involves rupture of the dimer in a manner akin to that observed at high temperature and ambient pressure. The response of the S···S-S···S σ-bond in β-1a to heat and pressure is compared to that of related dimers possessing S···Se-Se···S σ-bonds.
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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 | 0.001 |
| 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 it