Interaction Between the Rubidium Cation and [2.2.2]Paracyclophane: Experimental and Theoretical Study.

By means of electrospray ionization mass spectrometry (ESI-MS), it was evidenced experimentally that the rubidium cation (Rb+) reacts with the electroneutral [2.2.2]paracyclophane ligand (C24H24) to form the cationic complex [Rb(C24H24)]+. Moreover, applying quantum chemical calculations, the most probable conformation of the proven [Rb(C24H24)]+ complex was solved. In the complex [Rb(C24H24)]+ having a symmetry very close to C3, the "central" cation Rb+, fully located in the cavity of the parent [2.2.2]paracyclophane ligand, is coordinated to all three benzene rings of [2.2.2]paracyclophane via cation-π interaction. Finally, the binding energy, E(int), of the considered cation-π complex [Rb(C24H24)]+ was evaluated as -99.3 kJ/mol, confirming the formation of this fascinating complex species as well. This means that the [2.2.2]paracyclophane ligand can be considered as a receptor for the rubidium cation in the gas phase.