Abstract
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.
Highlights
It is well-known that π-prismands and certain hydrocarbon cyclophanes are capable of forming π-complexes with some small metal cations, where benzene rings act as π-donors for the respective complexes.[1]
In the present work, electrospray ionization mass spectrometry (ESI-MS) was applied as an experimental technique for characterization of the cation-π interaction between the very voluminous heavy univalent rubidium cation (Rb+) and this [2.2.2]paracyclophane ligand in the gas phase. In this context we must state that the cation Rb+ was chosen for the present study especially for the sake of an expected fascinating structure of the resulting cationic complex involving the [2.2.2]paracyclophane ligand
It is necessary to emphasize that under the present experimental conditions, the cationic complex species [Rb(C24H24)]+ was proven in the gas phase
Summary
It is well-known that π-prismands and certain hydrocarbon cyclophanes are capable of forming π-complexes with some small metal cations, where benzene rings act as π-donors for the respective complexes.[1]. In the present work, electrospray ionization mass spectrometry (ESI-MS) was applied as an experimental technique for characterization of the cation-π interaction between the very voluminous heavy univalent rubidium cation (Rb+) and this [2.2.2]paracyclophane ligand in the gas phase.
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