Fulleride

Using the technique cyclic voltammetry, C60 can be shown to undergo six reversible reductions starting at −1 V referenced to the Fc+/Fc couple.

In certain cases, e.g. [PPN]2C60, the structures are highly ordered and slight (10 pm) elongation of some C−C bonds is observed.

However, this ammoniation technique has revealed a new aspect of fullerene intercalation compounds: the Mott transition and the correlation between the orientation/orbital order of C60 molecules and the magnetic structure.

[11] This apparent anomaly may be explained by the Jahn–Teller effect, where spontaneous deformations of high-symmetry molecules induce the splitting of degenerate levels to gain the electronic energy.

[10] A narrow band or strongly correlated electronic system and degenerated ground states are relevant to explaining superconductivity in fulleride solids.

When the interelectron repulsion U is greater than the bandwidth, an insulating localized electron ground state is produced in the simple Mott–Hubbard model.

The application of high pressure decreases the interfullerene spacing, therefore caesium-doped C60 solids turn to metallic and superconducting.