Reversible SO<sub>2</sub> Uptake by Tetraalkylammonium Halides: Energetics and Structural Aspects of Adduct Formation Between SO<sub>2</sub> and Halide Ions
Bibliographic record
Abstract
Abstract Contact with SO2 causes almost immediate dissolution of tetraalkylammonium halides, R4NX, (R = CH3 (Me), X = I; R = C2H5 (Et), X = Cl, Br, I; R = C4H9 (nBu), X = Cl, Br), with the formation of an adduct, [R4N]+[(SO2)nX]– (n = 1–4). Vapor pressure measurements indicate the proclivity for SO2 uptake follows the order N(CH3)4+ < N(C2H5)4+ < N(C4H9)4+. This trend is in accord with the Jenkins–Passmore volume‐based thermodynamic model. Born–Haber cycles, incorporating the lattice energy and gas phase energy terms, are used to evaluate the energetic feasibility of reactions. Density functional theory calculations (B3PW91; 6‐311+G(3df)) have been used to calculate the energetics of (SO2)nX– (X = Cl and Br) anions in the gas phase. The experimental studies show that tetraalkylammonium halides are feasible sorbents for SO2. In order to correlate the theoretical model, experimental enthalpy, ΔrH° and entropy, ΔrS° changes have been determined by the van't Hoff method for the binding of one SO2 molecule to (C2H5)4NCl, resulting in the liquid adduct (C2H5)4NCl·SO2. The structure of the analogous 1:1 bromide adduct, (C2H5)4NBr·SO2, has been determined by single‐crystal X‐ray diffraction (monoclinic, P21/c, a = 9.1409(14) Å, b = 12.3790(19) Å, c = 11.3851(17) Å, β = 107.952(2)°, V = 1225.6(3) Å3). The structure consists of discrete alkylammonium cations, bromide anions and SO2 molecules with short contacts between the anion and SO2 molecules. The (C2H5)4N+ cationadopts a transoid conformation with D2d symmetry, and represents a rare example of a well‐ordered (C2H5)4N+ cation in a crystal structure. The Br– anions and SO2 molecules forms a chain, (SO2Br–)n, with bifurcated contacts. Non‐bonding electron pairs on the halide anions engage in electrostatic interactions with the sulfur atoms and charge‐transfer interactions with the antibonding S–O orbitals of the bound SO2 moiety. Raman and 17O NMR spectra provide compelling evidence for a charge‐transfer interaction between SO2 molecules and the halide ions.
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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".