Exceptionally Long (≥2.9 Å) C−C Bonds between [TCNE]− Ions: Two-Electron, Four-Center π*-π* C−C Bonding in π-[TCNE]22−

Abstract

Attractive interaction with the cation overcomes the electrostatic repulsion between two tetracyanoethylene radical anions, [TCNE]^.- , and leads to the formation of a diamagnetic dimer [TCNE]₂^2- , for example, in [K(glyme)]₂ [TCNE]₂ . The bonding is described as two-electron, four-center bonding arising from π*-π* overlap. Crystallographic as well as spectroscopic (IR and UV/Vis) features of this bonding are observed.