The isolation, characterisation, gas phase electron diffraction and crystal structure of the thermally stable radical [CF3CSNSCCF3]˙ †
Bibliographic record
Abstract
The first structural characterisation of a heterocyclic free radical in all phases has been achieved. 4,5-Bis(trifluoromethyl)-1,3,2-dithiazol-2-yl, [CF3CSNSCCF3]˙ 4d, a 7π radical, was prepared quantitatively on reduction of [4d][AsF6] with various reducing agents. It is a blue gas over a green paramagnetic liquid [19F NMR δ −59.7], which freezes to a diamagnetic black-green solid. There is a remarkably large volume increase on melting implying that the liquid consists of discrete monomeric radicals, and consistently there is no tendency to dimerise in CCl3F solution and the vibrational spectra attributable to the monomer are essentially identical in all phases. The thermodynamic properties obtained for the vapourisation, sublimation and melting processes are very similar to those of related diamagnetic materials. 4d is remarkably thermochemically robust giving decomposition products identical to those from photochemical decomposition, a quantitative mixture of CF3CSSCCF3 (and its oligomers) and CF3CNSNCCF3. The reaction chemistry is described. The crystal structure shows radical 4d to be a planar heterocyclic ring which associates in the solid as a diamagnetic tetramer. The structure of the gaseous monomer determined by electron diffraction is very similar to that in the solid phase. Comprehensive physical measurements were made including the UV-visible spectra of the bright blue solutions, variable temperature magnetic susceptibility and quantitative variable temperature ESR spectra both of which confirm a phase change from a diamagnetic solid to a paramagnetic liquid on melting, the vibrational spectra, and the photoelectron spectrum of the gaseous free radical. A study of the behavior of RCSNSCR˙ (R = H, CH3 or CF3) given by the reduction of RCSNSCR+ on increase of concentrations of radical is reported, including the isolation of HCSNSCCF3˙ at low temperature. The experimental and calculated [UMPW1PW91/6-31+G*] structures of 4d are in good agreement. These and related calculations also support the interpretation of the vibrational and photoelectron spectra, and the thermodynamic properties of 4d, as well as provide possible explanations for the relative stabilities of RCSNSCR˙, and imply that the weak intramolecular interactions in 4d in the solid state are largely ionic Sδ+⋯Nδ− interactions.
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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 | 0.000 |
| 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".