Systematic Trends in the Electrochemical Properties of Transition Metal Hydride Complexes Discovered by Using the Ligand Acidity Constant Equation
Bibliographic record
Abstract
Understanding the thermodynamics of paramagnetic transition metal hydride complexes, especially of the abundant 3 d metals, is important in the design of electrocatalysts and organometallic catalysts. The p K a MeCN ([MHL n ] + /[ML n ) of paramagnetic hydrides in MeCN are estimated for the first time using the ligand acidity constant (LAC) equation where contributions to the p K a MeCN from each ligand are simply added together, with the sum corrected for effects of charge and 5 d metals. The p K a LAC–MeCN ([MHL n ] + /ML n ) of over 200 hydride complexes MHL n are used, along with their electrochemical potentials from the literature, in an uncommonly applied thermochemical cycle in order to reveal systematic trends in the redox couples M III/II and M V/IV (M = Cr, Mo, W), Mn II/I, Re VI/V and Re IV/III, M III/II and M IV/III (M = Fe, Ru, Os), and M III/II and M II/I (M = Co, Rh, and Ir) and allow the estimation of the bond dissociation free energies BDFE(MH) of the unoxidized hydrides MHL n and the prediction of the electrochemical potential for their oxidation. Density functional theory (DFT) calculations are used to validate the p K a LAC–MeCN values of hydrides of W III, Mn II, Fe III, Ru III, Co II, and Ni III . When a p K a LAC–MeCN is less than zero for a given complex [MHL n ] +, the oxidation of MHL n is irreversible due to proton loss from the oxidized complex to the solvent. When p K a LAC–MeCN ≫ 0, the oxidation is reversible when there is no gross change in the coordination geometry upon a change in the redox state. Twenty paramagnetic hydrides prepared in bulk all have p K a LAC–MeCN > 8.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 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 | 0.001 |
| 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 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".