On the existence of long C-C bonds between pairs of anions which repel: when and why? A test case on the [TCNE]22- dimers found in ionic crystals*

Journal ArticleMany of the Cm[TCNE]n (C = cation) salts have intradimer C-C interactions in the range of 2.9 to 3.5 A(°) and show the electronic fingerprints associated with C-C bond formation (IR and UV spectra, magnetic properties, structural changes), despite the fact that two [TCNE].- anions should repel each other due to purely Coulombic considerations. Herein, we analyze these pairwise interactions in detail for a particular crystal in which such a C-C bond is found, to understand when and why these bonds are formed in a general case