Intra-host π–π interactions in crown ether complexes revealed by cryogenic ion mobility-mass spectrometry

Abstract

Cryogenic ion mobility-mass spectrometry was performed to investigate the relative abundance of conformers of dinaphtho-24-crown-8 (DN24C8) complexes with alkali metal cations M⁺ (M = Li, Na, K, Rb, and Cs). The “closed” conformers of M⁺(DN24C8) with short distances between two naphthalene rings in the crown ethers were predominantly observed for all complexes at 86 K. The two noncovalent interactions, host–guest and intra-host interactions, were analyzed separately by density functional theory calculations to reveal the origin of the stability of the closed conformers. As a result, it was revealed that the intra-host π–π interactions have a more critical role in determining the stability of the conformers than the host–guest interactions. The closed conformers of M⁺(DN24C8) also have wider regions of the π–π interactions than those of the M⁺(dibenzo-24-crown-8) complexes.