Ion Selectivity of Crown Ethers Investigated by UV and IR Spectroscopy in a Cold Ion Trap

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• 作者：Yoshiya Inokuchi ; Oleg V. Boyarkin ; Ryoji Kusaka ; Takeharu Haino ; Takayuki Ebata ; Thomas R. Rizzo
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：April 26, 2012
• 年：2012
• 卷：116
• 期：16
• 页码：4057-4068
• 全文大小：757K
• 年卷期：v.116,no.16(April 26, 2012)
• ISSN：1520-5215

文摘

Electronic and vibrational spectra of benzo-15-crown-5 (B15C5) and benzo-18-crown-6 (B18C6) complexes with alkali metal ions, M⁺鈥15C5 and M⁺鈥18C6 (M = Li, Na, K, Rb, and Cs), are measured using UV photodissociation (UVPD) and IR鈥揢V double resonance spectroscopy in a cold, 22-pole ion trap. We determine the structure of conformers with the aid of density functional theory calculations. In the Na⁺鈥15C5 and K⁺鈥18C6 complexes, the crown ethers open the most and hold the metal ions at the center of the ether ring, demonstrating an optimum matching in size between the cavity of the crown ethers and the metal ions. For smaller ions, the crown ethers deform the ether ring to decrease the distance and increase the interaction between the metal ions and oxygen atoms; the metal ions are completely surrounded by the ether ring. In the case of larger ions, the metal ions are too large to enter the crown cavity and are positioned on it, leaving one of its sides open for further solvation. Thermochemistry data calculated on the basis of the stable conformers of the complexes suggest that the ion selectivity of crown ethers is controlled primarily by the enthalpy change for the complex formation in solution, which depends strongly on the complex structure.