Influence of Electron-Withdrawing Substituents on the Electronic Structure of Oxidized Ni and Cu Salen Complexes
Bibliographic record
Abstract
Nickel (Ni(Sal(CF3))) and copper (Cu(Sal(CF3))) complexes of an electron-poor salen ligand were prepared, and their one-electron oxidized counterparts were studied using an array of spectroscopic and theoretical methods. The electrochemistry of both complexes exhibited quasi-reversible redox processes at higher potentials in comparison to the M(Sal(R)) (R = (t)Bu, OMe, NMe2) analogues, in line with the electron-withdrawing nature of the para-CF3 substituent. Chemical oxidation, monitored by ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy, afforded their corresponding one-electron oxidized products. Ligand-based oxidation was observed for [Ni(Sal(CF3))](+•), as evidenced by sharp NIR transitions in the UV-vis-NIR spectrum and a broad isotropic signal at g = 2.067 by solution electron paramagnetic resonance (EPR) spectroscopy. Such sharp NIR transitions observed for [Ni(Sal(CF3))](+•) are indicative of a delocalized electronic structure, which is in good agreement with electrochemical measurements and density functional theory (DFT) calculations. In addition, the increased Lewis acidity of [Ni(Sal(CF3))](+•), evident from the EPR g-value and DFT calculations, was further quantified by the binding affinity of axial ligands to [Ni(Sal(CF3))](+•). For [Cu(Sal(CF3))](+), an intense ligand-to-metal charge transfer band at 18 700 cm(-1) in the UV-vis-NIR spectrum was observed, which is diagnostic for the formation of a Cu(III) species [J. Am. Chem. Soc., 2008, 130, 15448-15459]. The Cu(III) character for [Cu(Sal(CF3))](+) is further confirmed by (19)F NMR analysis. Taken together, these results show that the electron-deficient salen ligand H2Sal(CF3) increases the Lewis acidity of the coordinating metal center.
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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".