CF 3 : An Electron‐Withdrawing Substituent for Aromatic Anion Acceptors? “Side‐On” versus “On‐Top” Binding of Halides

The ability of multiple CF 3 ‐substituted arenes to act as acceptors for anions is investigated. The results of quantum‐chemical calculations show that a high degree of trifluoromethyl substitution at the aromatic ring results in a positive quadrupole moment. However, depending on the polarizability of the anion and on the substitution at the arene, three different modes of interaction, namely Meisenheimer complex, side‐on hydrogen bonding, or anion–π interaction, can occur. Experimentally, the side‐on as well as a η 2 ‐type π‐complex are observed in the crystal, whereas in solution only side‐on binding is found.