Molecular Orbitals for Metal Sandwich Compounds

A metal sandwich compound does not strictly fit our previous concept of an ABfl-type molecule, since the ligand atoms interact strongly with each other as well as with the central atom. It is desirable to extend the discussion to these molecules, however, since they provide clear and important examples of how to treat the situation in which the ligands in a complex are themselves polyatomic entities with an internal set of MOs perturbed by interaction with the AOs of the central atom. 

Using ferrocene, (QHs Fe, as an example, we can demonstrate all of the basic ideas in the MO treatment for the whole class of molecules. Accordingly, we will first treat ferrocene in detail then briefly outline the application of the method to a few other selected cases. 

Referring to the character table for group we see that an Alg orbital must be symmetric to inversion in the center of symmetry. This requirement 

a simple check will show that this orbital, satisfies all the 

For the E, and E2 orbitals we proceed in exactly the same way, choosing normalized combinations of the E, and E2 orbitals of the individual rings so as to obtain functions which are symmetric and antisymmetric to inversion, namely, 

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