Counterintuitive Isomerization of TFSI<sup>–</sup> and TFSI<sup>–</sup>–Cation Correlated Isomerization: Insights into the Low Melting Points of TFSI<sup>–</sup>-Based Ionic Liquids
Bibliographic record
Abstract
Ionic liquids (ILs), particularly bis(trifluoromethane)sulfonamide (TFSI – )-based ILs, have attracted substantial attention in electrochemical energy storage, ionic gating for superconductivity, and iontronic sensing. However, underestimating TFSI – isomerization and overlooking TFSI – –cation correlation make the origin of their most characteristic property, low melting points ( T m ), ambiguous. Traditional static electronic structure calculations assume that C 2 -symmetric trans enantiomers of TFSI – easily isomerize into cis enantiomers through four symmetrically equivalent pathways over a barrier of 7.1 kJ mol –1 . Herein, ab initio molecular dynamics (AIMD) simulations combined with metadynamics reveal that the unusual oscillation of the central nitrogen atom promotes TFSI – to undergo complex isomerization. Specifically, asymmetric trans -to- cis diastereomers of TFSI – experience restricted interconversion (20–52 kJ mol –1 ) through four distinct asymmetric pathways. The adaptive oscillation and hybridization of chiral nitrogen boost n N → σ* S–C negative hyperconjugation for stabilizing conformational structures and enlarging energy barriers. The orientational distortion of oxygen atoms’ lone pairs enhances conjugation but breaks the C 2 -symmetry. The coexistence of both helicity and chiral nitrogen breaks the enantiomeric relationship. Furthermore, Raman characterization and AIMD simulations confirm the positive correlation between the relative stability of cis -TFSI – and its countercation’s polarity. TFSI – and countercations make a mutual conformational selection instead of free isomerization. Surprisingly, T m increases with the cation-dependent conformational rigidity of TFSI –, offering new fundamental insights into the low T m of ILs. This descriptor encoding the dependence of thermal property on cation–anion correlated isomerization provides material design guidelines and property prediction capability.
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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) | 0.002 | 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".