Binuclear Hexa- and Pentavalent Uranium Complexes with a Polypyrrolic Ligand: A Density Functional Study of Water- and Hydronium-Induced Reactions
Bibliographic record
Abstract
Binuclear uranyl (VI) and (V) complexes of a Pacman-like polypyrrolic macrocycle (H(4)L) were investigated using relativistic density functional theory. The reactivity of the bis-uranyl(VI) complex (UO(2))(2)(L) (2a) was explored computationally. Although 2a has not been obtained experimentally, its structural analogue [(UO(2))(OH)K(THF)(2)(H(2)L(Me))] has been synthesized recently. The high reactive activity of 2a originates from its unique butterfly like cation-cation structure, containing an active O center with easily broken U-O bonding and having unsaturated coordination sites of uranium(VI) along the equatorial plane. The present study indicates that 2a can react with water (Path 3) and hydronium (Path 4), which lead to the formation of a series of complexes with a triangle-like O=U=O=U=O skeleton. Path 3 results in an unusual complex containing a combined cis-uranyl/trans-uranyl cation-cation structure, (cis-UO(2))(trans-UO(2))(H(2)O)(L) (4b), where the oxo atom of the trans-uranyl coordinates the uranium center of the cis-uranyl and the water bonds to the uranium of trans-uranyl in the equatorial plane. After a process of hydrogen transfer with an extremely low energy barrier (<1.5 kcal/mol), 4b is converted into a slightly more stable isomer (U(2)O(3))(OH)(2)(L) (4a), where two hydroxyl groups link to two uranium atoms, respectively. In conjunction with previous studies, the free energies of reactions of 2a induced by isomerization (Path 1), proton (Path 2), water (Path 3), and hydronium (Path 4) were calculated in the gas phase and aqueous solution. Solvation stabilizes the free energy of the formation reactions of the neutral complexes but destabilizes that of the charged complexes. In these reactions, three pairs of isomers were obtained for binuclear uranium(VI) complexes, but only the most stable in each pair exists for the binuclear uranium(V) analogues.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".