Structural, electronic and spectroscopic features of the dihydride Pd<sub>4</sub>(dppm)<sub>4</sub>(H)<sub>2</sub><sup>2+</sup> cluster catalyst
Bibliographic record
Abstract
1H NMR, vibrational, and UVvis spectroscopic measurements for Pd2(dppm)2Cl2 (dppm = Ph2PCH2PPh2), [Pd4(dppm)4(X)2](BF4)2 (X = Cl, H), and [Pd4(dmpm)4(H)2](Br)2 (dmpm = Me2PCH2PMe2) were performed to address the structure of the recently identified title cluster. Its dmpm analogue was prepared from the reaction between Pd2(dmpm)2Br2 and NaBH4 in methanol under inert atmosphere, and exhibits the expected nonet (rel. int. 1:8:28:56:70:56:28:8:1) at 5.21 ppm (in (CD3)2CO), contrasting with that of Pd4(dppm)4(H)22+ (δ + 5.15 ppm, (CD3)2CO). This significant difference is explained by the presence of the PdH residues in the deshielding region of the dppm-phenyl groups. The vibrational spectra in the low-frequency region are consistent with a centrosymmetric structure, and a scattering at 144 cm1 in the FT-Raman spectra is observed; a peak that is assigned to ν(Pd2) on the basis of a comparison with the well established M2-bonded Pd2(dppm)2Cl2 data ((Pd2) = 149 cm1). On the basis of the qualitative temperature behavior of the band maxima and width, the two lowest energy absorption bands in the UVvis spectra are assigned to d σ [Formula: see text] d σ * type transition. EHMO computations predict four well-isolated frontier MO levels, defined as d σ *(Pd2)/d σ *(PdH) (LUMO + 1), d σ *(Pd2) (LUMO), d σ *(Pd2)/d σ *(PdH) (HOMO), and d σ (Pd2) (HOMO 1), and simple selection rules (u « g) indicate that only two low-energy electronic transitions are orbitally allowed, consistent with the UVvis findings. Computer modelings show the presence of large cavities above and under the Pd4 plane, described by inner-cavity nonbonded H···H distances of ~58 Å.Key words: cluster, palladium, hydride, structure, spectroscopy.
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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".