A Polyselenide with a Novel Se<sub>7</sub><sup>8–</sup> Unit: the Structure of Sr<sub>19–<i>x</i></sub>Pb<i><sub>x</sub></i>Ge<sub>11</sub>Se<sub>44</sub> with <i>x</i> = 5.0 and 6.4
Bibliographic record
Abstract
An unprecedented, planar Se78– unit with a threefold rotation axis was discovered in the new polyselenide Sr19–xPbxGe11Se44. Sr12.6Pb6.4Ge11Se44 crystallizes in the non‐centrosymmetric hexagonal space group P63 with unit cell dimensions of a = b = 19.9867(2) Å, c = 12.0546(1) Å, V = 4170.28(7) Å3, with two formula units per cell. Its structure contains isolated [GeSe4] tetrahedra, [Ge2Se7] dimers, and a novel, planar propeller‐shaped Se78– unit. The latter is unprecedented, but reminiscent of the isoelectronic pyramidal Se78– and I7– units. It consists of a central Se atom, to which three Se2 pairs with a short Se–Se bond are attached through a longer Se–Se distance, resulting in a central Se atom featuring 120° bond angles, and bridging Se atoms featuring an approximately linear coordination with a 179° bond angle. It can thus be written as [Se(Se2)3]8–. We characterized this unit using Gaussian calculations in comparison to the pyramidal Se78– unit, which may be described also as [Se(Se2)3]8–. The solid‐state material is a black semiconductor with an optical band‐gap of 1.8 eV, which supports the assignment of this charge.
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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) | 0.002 | 0.001 |
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".