In organic chemistry, the cyclopentadienyl anion or cyclopentadienide is an aromatic species with a formula of [C5H5]-. Its name derives from the molecule cyclopentadiene. Salts of the cyclopentadienyl anion can be stable, e.g., Sodium cyclopentadienide. more complex coordination compounds are known as cyclopentadienyl complexes, such as metallocene
The structure shown is a composite of five resonance contributors in which each carbon carries part of the negative charge.