Comparison of Cation-π and Anion-π Interactions by Way of Antiaromaticity

Abstract

Cation-π and anion-π interactions were studied in the Na⁺-substituted-COT and F-substituted-COT complexes (where substituted-COT is planar cyclooctatetraene with four X‒C≡C-substituents (X = OH, CH₃, H, F, and CN) using computational quantum chemistry methods. There are no direct electrostatic interactions of substituents with cations and anions in these complexes. The electron-donating and electron-withdrawing substituents lead to increase of the strength of cation-π and anion-π interactions, respectively. There are meaningful correlations between the Hammett constants and binding energies. The AIM analysis shows that the electron-donating and electron-withdrawing substituents lead to increase in electronic charge density values at ring critical points (RCPs) of the Na⁺-substituted-COT and F^–-substituted-COT complexes, respectively (compared to complexes with X = H). NMR calculations demonstrate that the cation-π interactions are consistent with more antiaromatic rings and the anion-π ones are in accord with less antiaromatic rings.