Emergence of Symmetry and Chirality in Crown Ether Complexes with Alkali Metal Cations

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• 作者：Bruno Martnez-Haya ; Paola Hurtado ; Ana R. Hortal ; Said Hamad ; Jeffrey D. Steill ; Jos Oomens
• 刊名：Journal of Physical Chemistry A
• 出版年：2010
• 出版时间：July 8, 2010
• 年：2010
• 卷：114
• 期：26
• 页码：7048-7054
• 全文大小：263K
• 年卷期：v.114,no.26(July 8, 2010)
• ISSN：1520-5215

文摘

Crown ethers provide a valuable benchmark for the comprehension of molecular recognition mediated by inclusion complexes. One of the most relevant crown ethers, 18-crown-6 (18c6), features a flexible six-oxygen cyclic backbone that is well-known for its selective cation binding. This study employs infrared spectroscopy and quantum mechanical calculations to elucidate the structure of the gas-phase complexes formed by the 18c6 ether with the alkali metal cations. It is shown that symmetric and chiral arrangements play a dominant role in the conformational landscape of the 18c6−alkali system. Most stable 18c6−M⁺ conformers are found to have symmetries C_3v and C₂ for Cs⁺, D_3d for K⁺, C₁ and D_3d for Na⁺, and D₂ for Li⁺. Remarkably, whereas the bare 18c6 ether is achiral, chirality emerges in the C₂ and D₂ 18c6−M⁺ conformations, both of which involve pairs of stable atropoisomers capable of acting as enantiomeric selective substrates.