Thermochemistry of icosahedral closo-dicarboranes: a composite ab initio quantum-chemical perspective
Bibliographic record
Abstract
We obtained accurate thermochemical properties for the ortho-, meta-, and para-dicarborane isomers (C 2 B 10 H 12 ) by means of explicitly correlated high-level thermochemical procedures. The thermochemical properties include heats of formation, isomerization energies, C–H and B–H bond dissociation energies (BDEs), and ionization potentials. Of these only the ionization potentials are known experimentally. Our best theoretical ionization potentials, obtained by means of the ab initio W1–F12 thermochemical protocol, was 241.50 kcal mol –1 (para-dicarborane), 238.45 kcal mol –1 (meta-dicarborane), and 236.54 kcal mol –1 (ortho-dicarborane). These values agree with the experimental values adopted by the National Institute of Standards and Technology (NIST) thermochemical tables to within overlapping uncertainties. However, they suggest that the experimental values may represent significant underestimations. For all isomers, the C–H BDEs are systematically higher than the B–H BDEs because of the relative stability of the boron-centred radicals. The C–H BDEs for the three isomers cluster within a narrow energetic interval, namely between 110.8 kcal mol –1 (para-dicarborane) and 111.7 kcal mol –1 (meta-dicarborane). The B–H BDEs cluster within a larger interval ranging between 105.8 and 108.1 kcal mol –1 (both obtained for ortho-dicarborane). We used our benchmark W1–F12 data to assess the performance of a number of lower cost composite ab initio methods. We found that the Gaussian-3 procedures (G3(MP2)B3 and G3B3) result in excellent performance with overall root-mean-square deviations (RMSDs) of 0.3–0.4 kcal mol –1 for the isomerization, ionization, and bond dissociation energies. However, the Gaussian-4 procedures (G4, G4(MP2), and G4(MP2)-6X) showed relatively poor performance with overall RMSDs of 1.3–3.7 kcal mol –1 .
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 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".