Cyclopentadienyl anion
In chemistry, the cyclopentadienyl anion or cyclopentadienide is an aromatic species with a formula of − and abbreviated as Cp−. Its name derives from the molecule cyclopentadiene.
It is a regular pentagonal, planar, cyclic ion; as well, it has 6 π-electrons, which fulfills Hückel's rule of aromaticity. It can coordinate as a ligand to metal atoms.
The structure shown is a composite of five resonance contributors in which each carbon atom carries part of the negative charge.
Salts of the cyclopentadienyl anion can be stable, e.g., sodium cyclopentadienide.
Coordination compounds of the cyclopentadienyl anion are known as cyclopentadienyl complexes. Biscyclopentadienyl complexes are called metallocenes.
