Crown Ether Inclusion Complexes of the Early Actinide Elements, [AnO<sub>2</sub>(18-crown-6)]<sup><i>n</i>+</sup>, An = U, Np, Pu and<i>n</i>= 1, 2: A Relativistic Density Functional Study
Bibliographic record
Abstract
The title compounds, [AnO2(18-crown-6)]n+, An = U, Np, and Pu and n = 1 and 2, as well as the related (experimentally observed) complex [UO2(dicyclohexyl-18-crown-6)]2+ are studied using relativistic density functional theory (DFT). Different relativistic methods (large-core and small-core effective core potentials, all-electron scalar four-component) and two flavors of approximate DFT (B3LYP and PBE) are used. Calculated bond lengths agree well with the available experimental data for the NpV complex, while larger differences for the UVI complexes appear to be related to the large uncertainties in the experimental data. The axial AnO bonds are found to be weaker and longer than in the corresponding penta-aquo complexes, though still of partial triple-bond character. The AnO bond lengths and strengths decrease along the actinide series, consistent with the actinide contraction. Gas-phase binding energies calculated for the penta-aquo complexes and crown-ether complexes of the actinides studied, as well as ligand-exchange energies, show that there is no intrinsic preference, or "better fit", for actinyl(V) cations as compared to actinyl(VI) ones. Rather, the ability of NpO2+ (NpV) to form in-cavity 18-crown-6 complexes in water, which is impossible for UO22+, is traced to solvation effects in polar solvents. Thus, the experimentally observed stabilization of the pentavalent oxidation state as compared to the hexavalent one is due to the effective screening of the charge provided by the macrocycle, and this leads to destabilization of the AnVI crown complexes relative to their AnV counterparts.
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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".