Computational and NMR Studies on the Complexation of Lithium Ion to 8‐Crown‐4

• Published in: Chemphyschem Vol. 20; no. 16; pp. 2103 - 2109
• Main Authors: van der Ham, Alex, Hansen, Thomas, Lodder, Gerrit, Codée, Jeroen D. C., Hamlin, Trevor A., Filippov, Dmitri V.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 16.08.2019; John Wiley and Sons Inc
• Subjects: activation strain model; Binding; Complexation; Crown ethers; density functional calculations; Density functional theory; Enthalpy; Ethers; Ions; Lithium; lithium ion binding; Lithium ions; Lithium isotopes; NMR spectroscopy; perching complex; Strain analysis; crown ethers; density functional calculations; lithium ion binding; perching complex; activation strain model
• ISSN: 1439-4235; 1439-7641; 1439-7641
• DOI: 10.1002/cphc.201900496

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. Lithium tops the crown! The binding of lithium ion to the smallest crown ether reported to date is governed by both entropic and enthalpic factors. Their intricate interplay is explicated by a combination of high‐level computations and a variety of 1H and 7Li NMR experiments.