Metallocene Bonding and Properties

Some of these questions are explained in the assigned readings, so please make sure you have done the reading before working out your answers.

1. What is the point group for the structure of ferrocene as determined by gas-phase electron diffraction?
2. How many nodes containing the z axis does the ferrocene LUMO have?
3. Make a detailed sketch of the ferrocene LUMO (both components) making clear which ring orbitals and which metal d orbital participates.
4. Make use of the direct product table for D_5h to determine for ferrocene which of the following electronic transitions is/are orbitally allowed: a₁′ (d) to LUMO, e₂′ (d) to LUMO, e₁′ (π) to LUMO, e₁′′ (π) to LUMO.
5. Which of the above transitions would be described as d-d bands, and which would be described as ligand-to-metal charge transfer (LMCT) bands?
6. Make a sketch of the ferrocene photoelectron spectrum and assign the peaks observed there. You may wish to refer to the interactive calculated molecular orbitals as an aid to your assignments.
7. Even though a single η⁵-Cp ligand gives rise to a ligand bond number of three according to the covalent bond classification method, and therefore ferrocene should have six metal-ligand bonds, the molecular orbital study of ferrocene reveals how many significant/major metal-ligand bonding interactions?
8. What is the symmetry (Mulliken symbol) for the most important metal-ring bonding molecular orbital in ferrocene.
9. Dilute solutions of ferrocene are pale yellow-orange, while one-electron oxidation of ferrocene gives the [Cp₂Fe]⁺ ion, which is dark blue. Why is ferrocenium ion so much more colored than ferrocene?
10. What is the dⁿ count of the ferrocenium ion?
11. Cobaltocene undergoes much more facile one-electron oxidation than does ferrocene. Explain.