High-Density Self-Assembled Monolayers of NHCs on Au(111) – Observation of Normal and Mesoionic Bonding Modes
Bibliographic record
Abstract
N-heterocyclic carbenes (NHCs) continue to attract interest as novel ligands for self–assembled monolayers on metals due to their propensity to form strong bonds to a variety of metals. However, understanding of the effect of NHC structural elements on adsorption geometry, NHC mobility, and on-surface intermolecular interactions remains limited. Herein we report the self-assembly of 1,3-diisopropyl imidazolylidene I-NHCiPr on Au(111) surfaces. This relatively simple NHC has never previously been examined on Au surfaces experimentally. We combine scanning tunnelling microscopy (STM) and density functional theory (DFT) calculations to provide detailed insight into this unique NHC-based SAM, which is the densest packed NHC-based SAM reported to date, utilizing approximately 14.5% of the available binding sites of the Au(111) surface. STM interrogations of the surface show the occasional formation of brighter adsorbates that we suggest can be attributed to metalation at the backbone C-4, rather than the expected C-2 site. This type of "abnormal" or mesoionic bonding mode is commonly observed in related organometallic compounds, suggesting that such complexes can provide a useful analogy for surface reactivity. The high density of the I-NHCiPr SAM and the generally high thermal and chemical robustness of NHC-based SAMs make this molecule ideally suited for a range of applications, providing an exciting platform for more complex surface functionalization.
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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".