A whopper of a carbon-carbon bond

Carbon-Carbon bonds that are 2.9 Å or longer have been identified in a small class of electron-transfer salts. Of these salts, cations assist pairs of tetracyanoethylene (TCNE) radical anions to overcome their electrostatic repulsion and form unusually long bonds between the ethylene carbons of two neighboring TCNE anions. These weak, elongated bonds, created by overlap of two singly occupied π* orbitals, involve four carbon atoms sharing two electrons.