The crystal structure of charmarite – the first case of a 11 × 11 Å superstructure mesh in layered double hydroxides
Bibliographic record
Abstract
Abstract Charmarite, Mn 4 Al 2 (OH) 12 CO 3 ⋅3H 2 O, is a hydrotalcite supergroup member (or layered double hydroxide, LDH) with a previously unknown crystal structure and a Mn 2+ -analogue of quintinite (commonly erroneously reported as ‘2:1 hydrotalcite’). The single-crystal X-ray diffraction (XRD) data were obtained from the specimen from Mont Saint-Hilaire, Québec, Canada and are best processed in the space group P $\bar{3}$ , a = 10.9630(4), c = 15.0732(5) Å and V = 1568.89(12) Å 3 . The crystal structure has been solved by direct methods and refined to R 1 = 0.0750 for 3801 unique reflections with F o > 2σ( F o ). The charmarite structure has long-range periodicity in the xy plane due to $2\sqrt 3$ a ’ × $2\sqrt 3$ a ’ scheme (or 11 × 11 Å) determined for LDHs for the first time (where a ’ is a subcell parameter ≈ 3.2 Å). This periodicity is produced by the combination of two superstructures formed by: (1) Mn 2+ and Al 3+ ordering in the metal-hydroxide layers [Mn 4 Al 2 (OH) 12 ] 2+ according to the $\sqrt 3$ a ’ × $\sqrt 3$ a ’ pattern and (2) the (CO 3 ) 2– ordering according to the 2 a ’ × 2 a ’ pattern in the [CO 3 (H 2 O) 3 ] 2– interlayer sheet in order to avoid close contacts between adjacent carbonate groups. The $2\sqrt 3$ a ’ × $2\sqrt 3$ a ’ superstructure is an example of the adaptability of the components of the interlayer space to the charge distribution of the metal-hydroxyl layers. The Mn 2+ and Al 3+ cations have a large difference in size, which apparently leads to the considerable degree of their order as di- and trivalent cations resulting in a higher degree of statistical order of the interlayer components. Both powder and single-crystal XRD data show that the samples studied belong to the hexagonal branch of two-layer polytypes (2 T or 2 H ) with d 00 n ≈ 7.57 Å. The chemical composition of the samples studied is close to the ideal formula. The Raman spectrum of charmarite is reported and the band assignment is provided.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 |
| 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 teacher head, 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".