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]22− (see picture), 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.