Calix[4]pyrrole: An Old yet New Ion‐Pair Receptor

Abstract

The development of ion-pair receptors, with the goal of achieving a higher level of control over recognition than that obtainable from simple ion binding, has intrigued researchers in supramolecular chemistry over the past decade.[1] Many reports have appeared during this period that describe the synthesis and study of very sophisticated receptor designs incorporating a range of electron-pair donor and acceptor groups. Most, if not all, of this work has been performed in the context of creating so-called ion-pair or salt hosts that will bind cation-anion pairs in homogeneous solution or enhance their extraction or transport under interfacial conditions. Whether the ditopic architecture in such systems confers real advantages over simpler combinations of single-ion receptors remains an open question. However, the utility of ion-pair

Anion Selectivity in Zwitterionic Amide‐Functionalised Metal Salt Extractants

“…The two phenol groups form intramolecular hydrogen bonds to the imine N centres, O1À H1···N1, dA C H T U N G T R E N N U N G (O···N) = 2.6121 (13) . There is a further intramolecular hydrogen bond between an NH group and the O centre of the urea in the pendant arm, N5 À H5B···O2, (14) . We have previously observed a similar intramolecular hydrogen bond forming a six-membered ring with this pendant arm when attached to an aza-thioether macrocycles.…”

“…The design of selective anion receptors is a rapidly expanding area, [11,12] and the simultaneous binding of both cationic and anionic moieties of metal salts by polytopic ligands with chemically distinct binding sites is currently a very active area of research. [12][13][14][15][16][17][18][19][20][21][22][23] Typically, many anion receptors use several non-covalent interactions to achieve strong binding, and hydrogen-bonding donor sites are most commonly incorporated into synthetic receptors, because their directionality allows steric and conformational control of the hydrogen-bond donors to match the requirements of anions of different sizes and ge-A C H T U N G T R E N N U N G ometries. A striking example of such a naturally occurring system is the phosphate-binding protein (PBP), which uses twelve hydrogen bonds including seven from amide NH groups to bind a monohydrogen phosphate anion selectively.…”

Exploring the Dynamics of Calix[4]pyrrole: Effect of Solvent and Fluorine Substitution

“…[1][2][3][4][5][6][7][8][9][10][11] One of the most popular and versatile chemical receptors is calix [4]pyrrole (mesooctaalkylporphyrinogens; CP), a molecule first synthesized more than 100 years ago, [12] but which only recently has been investigated as chemical receptor for small anions. [13][14][15][16][17][18][19][20][21][22][23][24] Abstract: Molecular dynamics simulations show that calix [4]pyrrole (CP) and octafluorocalix [4]pyrrole (8F-CP) are extremely flexible molecules. CP mainly adopts the 1,3-alternate conformation in all the solvents, although the percentage of alternative conformations increases in polar solvents, especially those with good hydrogen-bonding acceptor properties.…”

Aromatic and Aliphatic CH Hydrogen Bonds Fight for Chloride while Competing Alongside Ion Pairing within Triazolophanes

“…[22] In anion-receptor chemistry, however, only qualitative treatments of ion pairing have prevailed. [17,23] While these approaches have yielded insights into ion pairs, [24] anion transport, [25] ion-pair receptors, [26] and opportunities for template-directed syntheses, [27] the effect of the countercation on anion recognition has never been quantified.…”