Conservation of Helicity in a Chiral Pyrrol-2-yl Schiff-Base Ligand and Its Transition Metal Complexes
Bibliographic record
Abstract
Tetradentate enantiopure Schiff-base ligand (R,R) and (S,S)-bis(pyrrol-2-ylmethyleneamine)-cyclohexane (H2L) and its five transition metal complexes with Ni(II), Cu(II), Zn(II), Pd(II), and Pt(II) were synthesized. Their structural properties, in particular, the ligand chirality, coordination topology, and the resulting helicity in solution, were investigated by using IR, vibrational circular dichroism (VCD), UV-vis, and electronic circular dichroism (ECD) spectroscopies, complemented with density functional theory calculations. Conformational searches and the associated spectral simulations for the ligands and the complexes were performed at the B3LYP/Gen level. Comparison of the experimental and theoretical IR and VCD spectral signatures of these complexes reveal that the Zn complex takes on a dinuclear, distorted tetrahedral coordination topology around the metal centers, whereas the other four metal complexes adopt the mononuclear, distorted square-planar coordination arrangement in solution. The helicity of all systems studied was identified to be M with the (R,R) ligand and P with the (S,S) ligand, dictated by the ligand chirality and the strong preference for the chair configuration by the cyclohexane moiety. Furthermore, the resulting helicity was found to dominate the ECD spectral features, even though the helicity-determining angles are close to zero for the nearly square-planar metal complexes. The related VCD spectral features are sensitive to both helicity of the complex and the chirality of the ligands, as well as the coordination topology. The simulated ECD spectra for the P and M helicity of the [Zn-(R,R)-L]2 complex shows almost mirror-imaged ECD spectral features, whereas very similar ECD spectra were recently reported for the P- and M-dinuclear Mn complexes with a di-μ-oxo dimetal core as a linker. We highlight the advantages of utilizing multiple chiroptical techniques and theoretical spectral simulations to correlate chiroptical spectral features with multiple chirality and helicity elements in the systems.
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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".