Charge and Solvent Effects on the Redox Behavior of Vanadyl Salen-Crown Complexes
Bibliographic record
Abstract
The incorporation of charged groups proximal to a redox active transition metal center is an attractive strategy for altering redox behavior, installing electric fields, and enhancing catalysis. Vanadyl salen (salen = N,N-ethylenebis(salicylideneaminato)) complexes functionalized with a crown ether containing a non-redox active Lewis acidic metal cation (V-Na, V-K, V-Ba, V-La, V-Ce, and V-Nd) were synthesized. The electrochemical behavior of this series of complexes was investigated by cyclic voltammetry in solvents with varying polarity and dielectric constant (acetonitrile = 37.5; N,N-dimethylformamide = 36.7; and dichloromethane = 8.93). The vanadium(V/IV) reduction potential shifted anodically (>900 mV in acetonitrile and >700 mV in dichloromethane) with increasing cation charge as compared to complexes lacking the proximal cation. The reduction potential for all vanadyl salen-crown complexes measured in N,N-dimethylformamide was insensitive to cation charge magnitude, regardless of electrolyte or counter anion used. Titration studies of N,N-dimethylformamide into acetonitrile resulted in cathodic shifting of the vanadium(V/IV) reduction potential with increasing concentration of N,N-dimethylformamide. Binding constants of N,N-dimethylformamide (log(KDMF)) for the series of crown complexes show increased binding affinity in the order of V-La>V-Ba>V-K>(salen)V(O), indicating an enhancement of Lewis acid/base interaction with increase of cation charge. The redox behavior of (salen)V(O) and (salen-OMe)V(O) (salen-OMe = N,N-ethylenebis(3-methoxysalicylideneamine) was also investigated and compared to the crown-containing complexes. For (salen-OMe)V(O), a weak association of triflate salt at the vanadium(IV) oxidation state was observed through cyclic voltammetry titration experiments and cation dissociation upon oxidation to vanadium(V) was identified. These studies demonstrates the non-innocent role of solvent coordination and cation/anion effects on redox behavior.
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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".