Recognition and Extraction of Cesium Hydroxide and Carbonate by Using a Neutral Multitopic Ion‐Pair Receptor

Abstract

Current approaches to lowering the pH of basic media rely on the addition of a proton source. An alternative approach is described here that involves the liquid-liquid extraction-based removal of cesium salts, specifically CsOH and Cs2CO3, from highly basic media. A multitopic ion-pair receptor (2) is used that can recognize and extract the hydroxide and carbonate anions as their cesium salts, as confirmed by 1H NMR spectroscopic titrations, ICP-MS, single-crystal structural analyses and theoretical calculations. A sharp increase in the pH and cesium concentrations in the receiving phase is observed when receptor 2 is employed as a carrier in U-tube experiments involving the transport of CsOH through an intervening chloroform layer. The pH of the source phase likewise decreases.

Chalcogen Bond Mediated Enhancement of Cooperative Ion‐Pair Recognition

“…Charged species are ubiquitous,p laying crucial roles in biology,m edical healthcare and in particular in the environment resulting from polluting anthropogenic chemical industry activities.Cation and anion binding affinities of monotopic receptor systems are critically influenced by the nature of counterions.This has stimulated an ever increasing interest in the construction of heteroditopic receptors for ion-pair recognition, which are designed to enhance the efficacyo f charged guest recognition via favourable intramolecular electrostatic interactions and conformational allosteric cooperativity. [1][2][3][4] Such systems have been demonstrated to facilitate the solubilisation of inorganic salts in organic media, [5][6][7][8] to function as efficient extraction and membrane transport reagents, [9,10] and to be capable of recognising biologically relevant zwitterionic species. [11][12][13] Ah eteroditopic receptor typically utilizes Lewis acidic groups and most commonly,v arious hydrogen bond (HB) donor motifs for recognition of anion guest species.…”

From Heteroditopic to Multitopic Receptors for Ion‐Pair Recognition: Advances in Receptor Design and Applications

“…Whereas heteroditopic receptors contain a single binding site for each anion and cation, multitopic receptors have multiple binding sites for the cation and/or anion. [32] This section will focus on progress regarding the design of: receptors for binding MX-type ion-pairs via different binding modes; [11b,33] tritopic receptors for binding M 2 X or MX 2 -type ion-pairs; [17,34] and tetratopic [35] receptors. Calix [4]pyrrole functions as a heteroditopic receptor for ionpairs, [11a,36] and has recently been exploited by Bryantsev and Moyer in a supramolecular approach to modulate the selectivity of a cation exchanger, a lipophilic phenolate.…”

Enhancement of Ion Pairing of Sr(II) and Ba(II) Salts by a Tritopic Ion‐Pair Receptor in Solution

“…Additionally, the modification of the recognition sites allows for fine-tuning the selectivity, thus, a plethora of receptors has been designed for efficient binding of alkali metal (MX) and tetraalkylammonium salts (R 4 NX). As such, IP receptors have emerged as potential candidates for numerous applications, such as salt extraction, [12][13][14][15][16][17] transmembrane transport, [18][19][20][21][22][23] and catalysis. [24,25] The ability to tailor cationic and anionic binding sites also enables the design of multitopic receptors.…”

“…Since these receptors benefit from synergistic effects between the co‐bound ions, such as electrostatic and allosteric interactions, they exhibit enhanced binding affinities. Additionally, the modification of the recognition sites allows for fine‐tuning the selectivity, thus, a plethora of receptors has been designed for efficient binding of alkali metal (MX) and tetraalkylammonium salts (R 4 NX) . As such, IP receptors have emerged as potential candidates for numerous applications, such as salt extraction, transmembrane transport, and catalysis …”