Solving complex open-framework structures from X-ray powder diffraction by direct-space methods using composite building units
Bibliographic record
Abstract
The crystal structure of a novel open-framework gallogermanate, SU-66 {|(C6H18N2)18(H2O)32|[Ga4.8Ge87.2O208]}, has been solved from laboratory X-ray powder diffraction (XPD) data by using a direct-space structure solution algorithm and local structural information obtained from infrared (IR) spectroscopy. IR studies on 18 known germanates revealed that the bands in their IR spectra were characteristic of the different composite building units (CBUs) present in the structures. By comparing the bands corresponding to Ge—O vibrations in the IR spectra of SU-66 with those of the 18 known structures with different CBUs, the CBU of SU-66 could be identified empirically as the Ge10(O,OH)27 cluster (Ge10). The unit cell and space group (extinction symbol P--a; a = 14.963, b = 31.593, c = 18.759 Å) were determined initially from the XPD pattern and then confirmed by selected-area electron diffraction. The structure of SU-66 was solved from the XPD data using parallel tempering as implemented in FOX [Favre-Nicolin & Černý (2002). J. Appl. Cryst. 35, 734–743] by assuming P21 ma symmetry and two Ge10 clusters in the asymmetric unit. Rietveld refinement of the resulting structure using synchrotron XPD data showed the framework structure to be correct and the space group to be Pmma. The framework has extra-large (26-ring) one-dimensional channels and a very low framework density of 10.1 Ge/Ga atoms per 1000 Å3. SU-66, with 55 framework atoms in the asymmetric unit, is one of the more complicated framework structures solved from XPD data. Indeed, 98% of the reflections were overlapping in the XPD pattern used for structure solution. Tests on other open-framework germanates (SU-62, SU-65, SU-74, PKU-12 and ITQ-37) for which the XPD data, unit cell, space group and IR spectra were available proved to be equally successful. In a more complex case (SU-72) the combination of FOX and powder charge flipping was required for structure solution.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.002 | 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".