KF and CsF Recognition and Extraction by a Calix[4]crown‑5 Strapped Calix[4]pyrrole Multitopic Receptor

On the basis of ¹H NMR spectroscopic analyses and single crystal X-ray crystal structural data, the ion-pair receptor <b>1</b>, bearing a calix[4]­pyrrole for anion binding and calix[4]­arene crown-5 for cation recognition, was found to act as a receptor for both CsF and KF ion-pairs. Both substrates are bound strongly but via different binding modes and with different complexation dynamics. Specifically, exposure to KF in 10% CD₃OD in CDCl₃ leads first to complexation of the K⁺ cation by the calix[4]­arene crown-5 moiety. As the relative concentration of KF increases, then the calix[4]­pyrrole subunit binds the F^– anion. Once bound, the K⁺ cation and the F^– anion give rise to a stable 1:1 ion-pair complex that generally precipitates from solution. In contrast to what is seen with KF, the CsF ion-pair interacts with receptor <b>1</b> in two different modes in 10% CD₃OD in CDCl₃. In the first of these, the Cs⁺ cation interacts with the calix[4]­arene crown-5 ring weakly. In the second interaction mode, which is thermodynamically more stable, the Cs⁺ cation and the counteranion, F^–, are simultaneously bound to the receptor framework. Further proof that system <b>1</b> acts as a viable ion-pair receptor came from the finding that receptor <b>1</b> could extract KF from an aqueous phase into nitrobenzene, overcoming the high hydration energies of the K⁺ and F^– ions. It was more effective in this regard than a 1:1 mixture of the constituent cation and anion receptors (<b>4</b> and <b>5</b>)

Controlling Cesium Cation Recognition via Cation Metathesis within an Ion Pair Receptor

Ion pair receptor <b>3</b> bearing an anion binding site and multiple cation binding sites has been synthesized and shown to function in a novel binding–release cycle that does not necessarily require displacement to effect release. The receptor forms stable complexes with the test cesium salts, CsCl and CsNO₃, in solution (10% methanol-<i>d</i>₄ in chloroform-<i>d</i>) as inferred from ¹H NMR spectroscopic analyses. The addition of KClO₄ to these cesium salt complexes leads to a novel type of cation metathesis in which the “exchanged” cations occupy different binding sites. Specifically, K⁺ becomes bound at the expense of the Cs⁺ cation initially present in the complex. Under liquid–liquid conditions, receptor <b>3</b> is able to extract CsNO₃ and CsCl from an aqueous D₂O layer into nitrobenzene-<i>d</i>₅ as inferred from ¹H NMR spectroscopic analyses and radiotracer measurements. The Cs⁺ cation of the CsNO₃ extracted into the nitrobenzene phase by receptor <b>3</b> may be released into the aqueous phase by contacting the loaded nitrobenzene phase with an aqueous KClO₄ solution. Additional exposure of the nitrobenzene layer to chloroform and water gives <b>3</b> in its uncomplexed, ion-free form. This allows receptor <b>3</b> to be recovered for subsequent use. Support for the underlying complexation chemistry came from single-crystal X-ray diffraction analyses and gas-phase energy-minimization studies

Controlling Cesium Cation Recognition via Cation Metathesis within an Ion Pair Receptor

Ion pair receptor <b>3</b> bearing an anion binding site and multiple cation binding sites has been synthesized and shown to function in a novel binding–release cycle that does not necessarily require displacement to effect release. The receptor forms stable complexes with the test cesium salts, CsCl and CsNO₃, in solution (10% methanol-<i>d</i>₄ in chloroform-<i>d</i>) as inferred from ¹H NMR spectroscopic analyses. The addition of KClO₄ to these cesium salt complexes leads to a novel type of cation metathesis in which the “exchanged” cations occupy different binding sites. Specifically, K⁺ becomes bound at the expense of the Cs⁺ cation initially present in the complex. Under liquid–liquid conditions, receptor <b>3</b> is able to extract CsNO₃ and CsCl from an aqueous D₂O layer into nitrobenzene-<i>d</i>₅ as inferred from ¹H NMR spectroscopic analyses and radiotracer measurements. The Cs⁺ cation of the CsNO₃ extracted into the nitrobenzene phase by receptor <b>3</b> may be released into the aqueous phase by contacting the loaded nitrobenzene phase with an aqueous KClO₄ solution. Additional exposure of the nitrobenzene layer to chloroform and water gives <b>3</b> in its uncomplexed, ion-free form. This allows receptor <b>3</b> to be recovered for subsequent use. Support for the underlying complexation chemistry came from single-crystal X-ray diffraction analyses and gas-phase energy-minimization studies

Controlling Cesium Cation Recognition via Cation Metathesis within an Ion Pair Receptor

Ion pair receptor <b>3</b> bearing an anion binding site and multiple cation binding sites has been synthesized and shown to function in a novel binding–release cycle that does not necessarily require displacement to effect release. The receptor forms stable complexes with the test cesium salts, CsCl and CsNO₃, in solution (10% methanol-<i>d</i>₄ in chloroform-<i>d</i>) as inferred from ¹H NMR spectroscopic analyses. The addition of KClO₄ to these cesium salt complexes leads to a novel type of cation metathesis in which the “exchanged” cations occupy different binding sites. Specifically, K⁺ becomes bound at the expense of the Cs⁺ cation initially present in the complex. Under liquid–liquid conditions, receptor <b>3</b> is able to extract CsNO₃ and CsCl from an aqueous D₂O layer into nitrobenzene-<i>d</i>₅ as inferred from ¹H NMR spectroscopic analyses and radiotracer measurements. The Cs⁺ cation of the CsNO₃ extracted into the nitrobenzene phase by receptor <b>3</b> may be released into the aqueous phase by contacting the loaded nitrobenzene phase with an aqueous KClO₄ solution. Additional exposure of the nitrobenzene layer to chloroform and water gives <b>3</b> in its uncomplexed, ion-free form. This allows receptor <b>3</b> to be recovered for subsequent use. Support for the underlying complexation chemistry came from single-crystal X-ray diffraction analyses and gas-phase energy-minimization studies

Controlling Cesium Cation Recognition via Cation Metathesis within an Ion Pair Receptor

Ion pair receptor <b>3</b> bearing an anion binding site and multiple cation binding sites has been synthesized and shown to function in a novel binding–release cycle that does not necessarily require displacement to effect release. The receptor forms stable complexes with the test cesium salts, CsCl and CsNO₃, in solution (10% methanol-<i>d</i>₄ in chloroform-<i>d</i>) as inferred from ¹H NMR spectroscopic analyses. The addition of KClO₄ to these cesium salt complexes leads to a novel type of cation metathesis in which the “exchanged” cations occupy different binding sites. Specifically, K⁺ becomes bound at the expense of the Cs⁺ cation initially present in the complex. Under liquid–liquid conditions, receptor <b>3</b> is able to extract CsNO₃ and CsCl from an aqueous D₂O layer into nitrobenzene-<i>d</i>₅ as inferred from ¹H NMR spectroscopic analyses and radiotracer measurements. The Cs⁺ cation of the CsNO₃ extracted into the nitrobenzene phase by receptor <b>3</b> may be released into the aqueous phase by contacting the loaded nitrobenzene phase with an aqueous KClO₄ solution. Additional exposure of the nitrobenzene layer to chloroform and water gives <b>3</b> in its uncomplexed, ion-free form. This allows receptor <b>3</b> to be recovered for subsequent use. Support for the underlying complexation chemistry came from single-crystal X-ray diffraction analyses and gas-phase energy-minimization studies

Controlling Cesium Cation Recognition via Cation Metathesis within an Ion Pair Receptor

Ion pair receptor <b>3</b> bearing an anion binding site and multiple cation binding sites has been synthesized and shown to function in a novel binding–release cycle that does not necessarily require displacement to effect release. The receptor forms stable complexes with the test cesium salts, CsCl and CsNO₃, in solution (10% methanol-<i>d</i>₄ in chloroform-<i>d</i>) as inferred from ¹H NMR spectroscopic analyses. The addition of KClO₄ to these cesium salt complexes leads to a novel type of cation metathesis in which the “exchanged” cations occupy different binding sites. Specifically, K⁺ becomes bound at the expense of the Cs⁺ cation initially present in the complex. Under liquid–liquid conditions, receptor <b>3</b> is able to extract CsNO₃ and CsCl from an aqueous D₂O layer into nitrobenzene-<i>d</i>₅ as inferred from ¹H NMR spectroscopic analyses and radiotracer measurements. The Cs⁺ cation of the CsNO₃ extracted into the nitrobenzene phase by receptor <b>3</b> may be released into the aqueous phase by contacting the loaded nitrobenzene phase with an aqueous KClO₄ solution. Additional exposure of the nitrobenzene layer to chloroform and water gives <b>3</b> in its uncomplexed, ion-free form. This allows receptor <b>3</b> to be recovered for subsequent use. Support for the underlying complexation chemistry came from single-crystal X-ray diffraction analyses and gas-phase energy-minimization studies