Covalent d-Block Organometallics: Teaching Lewis Structures and sd/sd <sup>2</sup> Hybridization Gives Students Additional Explanations and Powerful Predictive Tools
Bibliographic record
Abstract
Despite tremendous efforts by instructors and textbook authors, students find it difficult to develop useful chemical intuitions about structures and key properties of the important d-block organometallic species that have a d 6, d 8, or d 10 d-electron count. A full molecular orbital analysis is not always practical, and crystal field theory, while generally useful, is too limited here. It would be helpful to give students of organometallic chemistry an additional toolkit for understanding highly covalent d-block compounds. Hybridization arguments involving s and d orbitals (such as sd/sd 2 hybridization for d 8 /d 6 systems) provide useful insight, as is known from the research literature but rarely taught in undergraduate courses. This article makes descriptions of bonding that are based on s,d-hybridized orbitals more accessible, targeted toward undergraduate teaching. Geometries of unusual low-coordinate structures can be predicted. An in-depth physical explanation for the trans influence is provided. A clear explanation is given for the higher stability of the cis isomers versus the trans isomers in square-planar d 8 complexes MR 2 L 2 (R = alkyl/aryl, L = relatively weakly bonded neutral ligand) and for the fac versus mer isomers in octahedral d 6 complexes MR 3 L 3 . Relevant to catalysis, it is explained why strongly donating ligands do not always facilitate oxidative addition and why 12-electron and 14-electron Pd(0) species are thermodynamically much more accessible than expected. The method capitalizes on first year knowledge, namely, the ability to write Lewis structures and to use hybridization arguments. It ties into the upper-year experience, including graduate school, where covalent d-block complexes may be encountered in research and where hybridization schemes will naturally emerge from using the natural bond orbital (NBO) formalism. It is discussed where the method might fit into the inorganic curriculum.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.003 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.027 | 0.007 |
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".