[Et4N]2[TCNE]2 (TCNE = tetracyanoethylene) - an example of an exceptionally long 2.827 Ã CC bond

Interest in organic compounds exhibiting unusually long CC bonds has been the subject of several recent studies.1-3 The longest sp3-sp3 C-C single bond reported to date is 1.73 A°,1,2 whereas several [TCNE]22- (TCNE = tetracyanoethylene) dimers have been recently reported to form cation-assisted, long, two-electron (pi*-pi*) CC bonds involving four carbon atoms. These CC bonds range from 2.833 to 3.09 A°. The cations range from electrostatically bonded Tl+4 and K+5 to large, bulky, non-coordinating cations such as [Cr(C6H6)2]+,6 [Fe(C5H4)2C3H6]+,7 and [TDAE]2+ [TDAE = (Me2N)2- CC(NMe2)2].4,8 Herein we report the structure, IR and UV-Vis spectroscopic properties of [Et4N]2[TCNE]2, a new example of the [TCNE]22- dimer, which exhibits the shortest (pi*-pi*) CC bond for this family of compounds.