THE CUPRITE-LIKE FRAMEWORK OF OCu4 TETRAHEDRA IN THE CRYSTAL STRUCTURE OF SYNTHETIC MELANOTHALLITE, Cu2OCl2, AND ITS NEGATIVE THERMAL EXPANSION
Bibliographic record
Abstract
Crystals of synthetic melanothallite, Cu2OCl2, have been prepared by chemical transport reactions. Its crystal structure (orthorhombic, Fddd, a 7.4691(15), b 9.5969(19), c 9.700(2) Å, V 695.3(2) Å3, Z = 8) has been refined to R1 = 0.028 (wR = 0.078; S = 1.180) on the basis of 346 unique observed reflections (|Fo | ≥ 4F). There is one symmetrically independent Cu atom in the structure, coordinated by two O and four Cl atoms. The mixed-ligand CuO2Cl4 octahedron shows strong Jahn–Teller (4 + 2)-distortion, with two O and two Cl atoms located in the equatorial plane and two Cl atoms in apical positions. The structure may be described as a three-dimensional framework formed by the cross-linking of chains of edge-sharing CuO2Cl2 squares. The chains are parallel to [110] and [¯110], and are linked to each other through the sharing of O atoms. The structure can also be described as an array of OCu4 oxocentered tetrahedra linked by the sharing of Cu corners into a cuprite-like three-dimensional framework, with cavities in the framework containing Cl anions. As established previously, melanothallite shows negative thermal expansion along the b axis of its unit cell (b = –26.7 10–6 °C–1), whereas thermal expansion along the a axis is positive and large (a = 50.6 10–6 + 25.2 10–9t °C–1). This thermal behavior is explained on the basis of a cross-linking of chains of edge-sharing CuO2Cl2 squares. In the room-temperature structure, two chains are inclined to each other by ~76°. When the temperature increases, the angle tends toward 90°, and the change of the angle between the two chains is accompanied by an increase of the a unit-cell parameter and by a decrease in the b parameter. This hinge mechanism provides an explanation for the high anisotropy
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".