Bond Energies and Bonding Interactions in Fe(CO)<sub>5</sub><sub>-</sub><i><sub>n</sub></i>(N<sub>2</sub>)<i><sub>n</sub></i> (<i>n</i> = 0−5) and Cr(CO)<sub>6</sub><sub>-</sub><i><sub>n</sub></i>(N<sub>2</sub>)<i><sub>n</sub></i> (<i>n</i> = 0−6) Complexes: Density Functional Theory Calculations and Comparisons to Experimental Data
Bibliographic record
Abstract
Metal−N 2 bond energies have been calculated for the Fe(CO) 5 - n (N 2 ) n ( n = 1−5) and Cr(CO) 6 - n (N 2 ) n ( n = 1−6) complexes using density-functional theory (DFT). Bond enthalpies calculated using the gradient corrected BP86 functional are in good agreement with the available experimental data. An energy decomposition procedure and a population analysis were performed for all of the complexes to quantitatively characterize the interactions of N 2 and CO with the relevant coordinatively unsaturated metal species. In all cases, the metal−N 2 bond is weaker than the metal−CO bond because CO is both a better donor and a better acceptor of electron density. Calculated bond energies for Cr−N 2 bonds for the lowest energy isomers of the chromium complexes are 24, 23, 22, 21, 20, and 25 kcal/mol for n = 1−6, respectively. The trend of decreasing bond energy with added N 2 ligands is a result of weaker orbital interactions. The exception is Cr(N 2 ) 6, which is predicted to be more stable than the CO containing complexes. This increase in stability is ascribed to the absence of a CO trans effect. In contrast, the Fe−N 2 bond energies for the lowest energy isomers in the series are 24, 17, 14, 10, and 5 kcal/mol for n = 1−5, respectively. Although iron has a larger orbital interaction with dinitrogen ligands than chromium, the 16-electron iron complexes have to deform substantially when going from their ground triplet states to their final pentacoordinated singlet geometries. An energy cost that increases as the number of N 2 ligands increases is associated with this deformation. For chromium complexes, this deformation term does not significantly decrease the bond energy, but the magnitude of this term becomes the dominant factor in the differences in bond energies in the dinitrogenated iron complexes.
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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 | 0.004 | 0.001 |
| Meta-epidemiology (narrow) | 0.008 | 0.009 |
| Meta-epidemiology (broad) | 0.009 | 0.004 |
| Bibliometrics | 0.002 | 0.005 |
| Science and technology studies | 0.007 | 0.006 |
| Scholarly communication | 0.002 | 0.007 |
| Open science | 0.005 | 0.006 |
| Research integrity | 0.002 | 0.011 |
| Insufficient payload (model declined to judge) | 0.000 | 0.001 |
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; both teacher heads agree on what is shown here.
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".