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

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. Conformations of dinaphtho-24-crown-8 complexes were investigated by cryogenic ion mobility-mass spectrometry. The closed conformers with short naphthalene-naphthalene distances were highly stabilized by intra-host π-π interaction.