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 3d metals, is important in the design of electrocatalysts and organometallic catalysts. The pKaMeCN([MHLn]+/[MLn) of paramagnetic hydrides in MeCN are estimated for the first time using the ligand acidity constant (LAC) equation where contributions to the pKaMeCN from each ligand are simply added together, with the sum corrected for effects of charge and 5d metals. The pKaLAC–MeCN([MHLn]+/MLn) of over 200 hydride complexes MHLn 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 MIII/II and MV/IV (M = Cr, Mo, W), MnII/I, ReVI/V and ReIV/III, MIII/II and MIV/III (M = Fe, Ru, Os), and MIII/II and MII/I (M = Co, Rh, and Ir) and allow the estimation of the bond dissociation free energies BDFE(MH) of the unoxidized hydrides MHLn and the prediction of the electrochemical potential for their oxidation. Density functional theory (DFT) calculations are used to validate the pKaLAC–MeCN values of hydrides of WIII, MnII, FeIII, RuIII, CoII, and NiIII. When a pKaLAC–MeCN is less than zero for a given complex [MHLn]+, the oxidation of MHLn is irreversible due to proton loss from the oxidized complex to the solvent. When pKaLAC–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 pKaLAC–MeCN > 8.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.001 |
| 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) | 0.000 | 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".