1. The 1st Non-IPR Fullerene: Sc2@C66
You see here the charge densities of fullerene molecule obtained by the MEM/Rietveld method using the synchrotron powder data.
And these are the fullerene structure determined from the charge density.
The charge densities clearly exhibit the configuration of 6 and 5-membered rings.
What we have here are the pair of the fused pentagon.
In addition, the bonding bridge of Sc2 dimmer can be seen through the carbon cage.
This was the first report of the finding and determination of the IPR violating fullerene structure.
When you see the charge density, you will find the concentration of electron distribution around fused pentagon.
This indicates the existence of strong electron polarization in molecule.
From the view point of application of metallofullerene, such a unbalanced localized charge distribution
found in this and
Is expected to produce novel electronic property.
C.R.Wang et al. Nature 408(2000)

2. 3D-Electron Density Distribution of Sc2@C66 as Determined by Synchrotron X-ray Powder Diffraction
RF=5.4%
Sc-Sc: 2.87(9)Å
Sc2
(1.4eÅ-3)
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