Derivatization of polyoxotungstates in aqueous solution. Exploration of the kinetic stability of cobalt(II)- and cobalt(III) derivatives of lacunary anions with pyridine and pyridine-type ligands
Bibliographic record
Abstract
Four complexes of cobalt(II) with lacunary polyoxotungstate ligands, α-[PW11O39Co(H2O)]5-, α-[SiW11O39Co(H2O)]6-, α1-, and α2-[P2W17O61Co(H2O)]8- have been examined as potential precursors to substitutionally inert derivatized polytungstates that are stable in aqueous solution at near neutral pH. Replacement of the terminal water ligand by pyridine is readily achieved and the rates of exchange between bound and free pyridine were determined from NMR line widths at temperatures between 24 and 48°C. Oxidation to the aquacobalt(III) and pyridinecobalt(III) polytungstates occurs at potentials between +0.64 V (for α1-P2W17O61Co(py)]8-) and +1.00 V (for α2-[P2W17O61Co(H2O)]8-). The cobalt(III) complexes (with the exception of α-[PW11O39Co(H2O)]4- which undergoes slow reduction by the solvent) were prepared by controlled potential electrolysis and by oxidation with potassium perdisulfate. The rates of pyridine substitution on the aquacobalt(III) complexes were determined and follow the sequence α1-[P2W17O61Co(H2O)]7- (~0.5 M-1 s-1) » α2-[P2W17O61Co(H2O)]7- ~ α-[SiW11O39Co(H2O)]5-. Cesium salts of α1-[P2W17O61CoIII(L)]7- (L = pyrazine, 4,4′-bipyridine, isonicotinic acid, and the ethyl ester of isonicotinoylglycylglycine) and the "dumbbell" 2:1 complex with bridging 4,4′-bipyridine were isolated and characterized by cyclic voltammetry and 1H NMR spectroscopy.Key words: lacunary polyoxotungstates, cobalt, ligand substitution, kinetics, redox.
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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 | 0.000 |
| 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 | 0.000 |
| 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".