In chemistry, the cyclooctatetraenide anion or cyclooctatetraenide, more precisely cyclooctatetraenediide, is an aromatic species with a formula of [C8H8]2− and abbreviated as COT2−.

More complex coordination compounds are known as cyclooctatetraenide complexes, such as the actinocenes.

The structure is a planar symmetric octagon stabilized by resonance, meaning each atom bears a charge of −⁠1/4⁠.

The length of the bond between carbon atoms is 1.432 Å.

[1] The structure can serve as a ligand with various metals.