NMR-Enhanced Crystallography Aids Open Metal–Organic Framework Discovery Using Solvent-Free Accelerated Aging
Bibliographic record
Abstract
We demonstrate the combined use of NMR-enhanced crystallography and solvent-free synthesis by accelerated aging (AA), for the discovery and structural characterization of a novel cadmium-based open metal–organic framework (MOF) belonging to the class of zeolitic imidazolate frameworks (ZIFs). Although solid-state NMR spectroscopy has been used to assist in structural characterization of crystalline solids by powder X-ray diffraction (PXRD), typically through quantification of the contents of the asymmetric unit, this work highlights how it can take a more active role in guiding structure determination, by elucidating the coordination environment of the metal node in a novel MOFs. Exploration of AA reactions of cadmium oxide (CdO) and 2-methylimidazole (H MeIm ) enabled the synthesis of not only the previously reported yqt1 -topology framework but also a new material ( 1 ) exhibiting a Cd/ MeIm ratio of 1:3, contrasting the 1:2 ratio expected for a ZIF. Structural characterization of 1 was enabled by using 111 Cd solid-state nuclear magnetic resonance (SSNMR) to provide information on the coordination environment of the cadmium node. Specifically, 111 Cd SSNMR experiments were conducted on a series of model compounds to correlate the cadmium coordination environment to the observed isotropic chemical shift, δ iso ( 111 Cd), followed by multinuclear SSNMR experiments on 1 to determine the nature of the metal coordination environment and the number of distinct chemical sites. This information was used in refinement of the molecular level structure from the available PXRD data, a technique termed NMR-enhanced crystallography, revealing that 1 is an open diamondoid ( dia ) topology Cd( MeIm ) 2 framework based on Cd 2+ ions tetrahedrally coordinated with MeIm – ligands and additional H MeIm guest molecules within the framework pores. Although AA was initially devised as a clean, mild route for making MOFs, these results provide a proof-of-principle of how, by combining it with SSNMR spectroscopy as a means to overcome limitations of PXRD structure determination, it can be used to screen for new solid phases in the absence of solvents, high temperatures, or mechanical impact that are inherent to other thermally-, solution-, or mechanochemically-based techniques.
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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".