[2.2.2]Paracyclophane as a receptor for the cesium cation in the gas phase

By using electrospray ionisation mass spectrometry, it was proven experimentally that the cesium cation (Cs⁺) forms with 2.2.2]paracyclophane (C₂₄H₂₄) the cationic complex Cs(C₂₄H₂₄)]⁺. Further, applying quantum chemical calculations, the most probable structure of the Cs(C₂₄H₂₄)]⁺ complex was derived. In the resulting complex with a symmetry very close to C₃, the ‘central’ cation Cs⁺, fully located in the cavity of the parent 2.2.2]paracyclophane ligand, is bound to all three benzene rings of 2.2.2]paracyclophane via cation–π interaction. Finally, the interaction energy, E(int), of the considered cation–π complex Cs(C₂₄H₂₄)]⁺ was found to be ?73.2 kJ/mol, confirming the formation of this fascinating complex species as well. This means that 2.2.2]paracyclophane can be considered as a receptor for the Cs⁺ cation in the gas phase.