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How are the 10 vertical bonds in Ferrocene (sandwich structure) connected, by what type of bonds?

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What is the real structure of ferrocene? Concerning the 10 vertical extra long bonds?

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    $\begingroup$ What do you mean by 'real structure'? If I'm not mistaken, we're looking right at it. $\endgroup$ – M.A.R. Sep 20 '15 at 20:19
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    $\begingroup$ The "bond lines" in the picture you show are only there to hint that there is some bonding between the rings and iron. But they are not to be interpreted in the sense of bonds in Lewis structures, so don't take them literally. For molecules containing transition metals Lewis structures are not very accurate in describing the actual bonding (this might be interesting in that context). $\endgroup$ – Philipp Sep 20 '15 at 20:33
  • $\begingroup$ Yes, but the question I am asking is how are the rings in 3-D SPACE ATTACHED TO THE Iron atom. The discovers & others for Ferrocene openly admitted they could not discover the actual COVALENT bonding type and the bond angles were not discoverable from their x-Ray diffraction patterns. I am looking for replays that can postulate the bonding TYPE, bonding angles and bond lengths, what fraction of the bond is from Fe & from Carbon. Might it be possible that the bonding is of the Pauling "bent-bonding" type. Also, what is the 3-D geometrical shape of the Iron Atom within the so-called sandwich? $\endgroup$ – Chuck Boldwyn Sep 21 '15 at 19:00
  • $\begingroup$ How does Iron form 10 or more bonds of any type? Can Iron form 20 bonds to Iron? What is the maximum # of bonds Iron can form from one iron atom? What is the geometrical 3D structure of the Iron atom within Ferrocene? $\endgroup$ – Chuck Boldwyn Sep 21 '15 at 19:28
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    $\begingroup$ @ChuckBoldwyn We know the structure of ferrocene. The C5 units are flat and symmetric and the iron forms the filling in a sandwich where the rings are parallel to each other on either side of the iron atom. You seem to be trying to impose a bonding structure made up of single bonds that doesn't (and probably can't) explain this structure. Only a more complex view of the bonding makes sense involving delocalised pi-orbitals from the rings and d-orbitals from the iron. No simple picture with single bonds captures this. $\endgroup$ – matt_black Sep 22 '15 at 0:10
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The "real" structure of ferrocene is an iron atom sandwiched between two flat, parallel, pentagonal C5H5 rings. The diagram above shows the atomic positions from a crystal structure but the bonds are merely a convenience and don't accurately summarize the way the bonding works though the picture does accurately summarize the atomic positions in the crystal structure.

The real bonding requires some understanding of molecular orbital theory and how the d-orbitals of iron interact with the delocalized pi-orbitals in the unsaturated ring. Some pictures of the orbitals contributing to the bonding are shown here.

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  • $\begingroup$ You are assuming all "p" orbitals & their bonding are only being used in bonding to Iron.....How about all sp3 orbitals & bonding coming from the carbon atoms attaching to whatever orbitals are extended from the Iron atom all as bent bonds. Could a structure, just proposed be possible or likely. Could this be a result of all free-radical bonding resulting in the Pauling proclaimed " banana bonds or bent bonding type? $\endgroup$ – Chuck Boldwyn Sep 21 '15 at 19:12
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    $\begingroup$ I didn't say anything about p-orbitals. The only way to really explain the structure is to think of molecular not atomic orbitals for the whole ring (which has delocalised pi-orbitals which interact with iron's d-orbitals). And we are not proposing a structure; we know the structure from x-ray and NMR evidence. All the carbons are equivalent and the structure looks like a sandwich with an iron filling. $\endgroup$ – matt_black Sep 22 '15 at 0:14
  • $\begingroup$ Are not pi orbitals made up of "p" orbitals overlapping vertically? I think when the cyclopentadieyl ring converts from sp2 carbon atoms to all sp3 carbon atoms, one would get simple cyclo pentane forming 5 sp3 bonds with the multi- valent Iron atom $\endgroup$ – Chuck Boldwyn Sep 22 '15 at 4:56
  • $\begingroup$ @ChuckBoldwyn The ring bonding doesn't "convert" to sp3 and the ring is aromatic with delocalised electrons. Pictures of the bonding that ignore this make no sense of the stability of structure of the molecule. $\endgroup$ – matt_black Sep 22 '15 at 7:56
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    $\begingroup$ @Maurice Why not posting this as a new question; preferentially setting sandwich complexes with 4, 5, and 6 carbon atoms on each side next to each other (same transition metal and oxidation state), and a check if these are are Hueckel aromatic. $\endgroup$ – Buttonwood Aug 10 at 17:28
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The pictures we use can inspire questions that are more complicated than they have to be. I like the hamburger picture of ferrocene:

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OK, there are some people who like a picture of some electron densities:

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Without going into the mathematics of all the orbitals, you can see that the filled orbitals on cyclopentadienide ion will have two lobes to donate into d-orbitals on ferrous ion. And there will be an electrostatic attraction between the cyclopentadienide ions and the ferrous ion.

The use of points and lines connecting them distorts the filled-space reality of the actual molecule. Of course, when you look at the filled-space models, you can't see exact bond lengths and angles, but it may give you a better idea of atoms fitting together, with molecular orbitals providing some sort of glue.

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