Computational and NMR Studies on the Complexation of Lithium Ion to 8-Crown-4 |
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Authors: | Alex van?der?Ham Thomas Hansen Dr Gerrit Lodder Dr Jeroen D C Codée Dr Trevor A Hamlin Dr Dmitri V Filippov |
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Institution: | 1. Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands;2. Department of Theoretical Chemistry, Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands |
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Abstract: | Lithium ion selective crown ethers have been the subject of much research for a multitude of applications. Current research is aimed at structurally rigidifying crown ethers, as restructuring of the crown ether ring upon ion binding is energetically unfavorable. In this work, the lithium ion binding ability of the relatively rigid 8-crown-4 was investigated both computationally by density functional theory calculations and experimentally by 1H and 7Li NMR spectroscopy. Although both computational and experimental results showed 8-crown-4 to bind lithium ion, this binding was found to be weak compared to larger crown ethers. The computational analysis revealed that the complexation is driven by enthalpy rather than entropy, illustrating that rigidity is only of nominal importance. To elucidate the origin of the favorable interaction of lithium ion with crown ethers, activation strain analyses and energy decomposition analyses were performed pointing to the favorable interaction being mainly electrostatic in nature. 8-crown-4 presents the smallest crown ether reported to date capable of binding lithium ion, possessing two distinct conformations from which it is able to do so. |
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Keywords: | activation strain model density functional calculations crown ethers lithium ion binding perching complex |
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