Where is the Anion Extraction Going?

Abstract

Reactive extraction processes represent efficient and smart technologies for separation and concentration of metal ions in solution, which are frequently used in industry. Despite the importance of anions in biology, medicine, environment and industry, practical examples of anion extraction are relatively limited compared to metal ion separation. Anion extraction processes are mainly based on the nonspecific ion pair formation with hydrophobic ammonium cations. In this case the phase transfer of anions is dominated by their lipophilicity. The reasons for this situation are closely connected with the specific features of anions in contrast to cations. Novel approaches for specific binding and selective transport of anionic components are based both on the better understanding of the biological role of anions and on the possibilities of supramolecular chemistry to create receptor architectures with complementary binding modes for anions. In the given review the authors discuss present research tendencies and application possibilities of new extractant types for separation and concentration of anionic species in solution.

Immobilization, Trapping, and Anion Exchange of Perrhenate Ion Using Copper-Based Tripodal Complexes

“…25 Because technetium is radioactive with a long half-life (~10 6 years), we decided to use perrhenate as a model of pertechnetate for these studies. Table 2 reveals that the geometric features of perrhenate and pertechnetate, including the radii of the metal center, 30 metal-oxo bond lengths, 31 and effective ionic radii of the two tetraoxoanions, 1,32 are very similar. Because they have the same tetrahedral geometry, similar charge density, and closely related chemical properties, perrhenate is a good model of pertechnetate and should behave in a nearly identical manner in anion trapping studies.…”

“…[1][2][3][4][5][6][7][8] Because anions regulate a variety of physiological processes, they are potential toxins. As examples, perchlorate ion can adversely affect human health by interfering with iodide uptake into the thyroid, [9][10][11] and chromate (CrO 4 2-) is toxic, mutagenic, and a human carcinogen.…”

Selective Extraction and Transport of the [PtCl6]2−Anion through Outer‐Sphere Coordination Chemistry

“…Back-extraction studies: Back extractions were performed to establish the use of a pH-swing mechanism to control the uptake and release of the [PtCl 6 ] 2À anion and also to determine the amount of platinum present in the organic phase in a mass balance equation. Yoshizawa 2À was A C H T U N G T R E N N U N G achieved and a mixing time of 30 min was found to be sufficient.…”

“…Selectivity continues to be a challenge in the development of supramolecular recognition of anions, [5] and is a pervasive problem in extractive metallurgy because the generation of electrolytes of high purity is essential for efficient electrolytic reduction to produce metals. [6] Thus, an understanding of the nature and disposition of electrostatic and supramolecular hydrogen-bonding interactions to chlo-A C H T U N G T R E N N U N G rometallates is essential in the design of selective extractants for these anions. DFT calculations and NMR spectroscopic studies of the solvation and ion pairing of [PtCl 6 ] 2À suggest that hydrogen-bonded solvate molecules, such as methanol, address the triangular faces of the hexachloro octahedron, [7] whereas formation of trifurcated hydrogen bonds to the faces, or bifurcated hydrogen bonding to the edges of the hexachloro octahedron has been predicted on the basis of the location of maximum electron density in the anion; [8] such interactions have indeed been observed in solid-state structures of chlorometallates.…”

Selective recognition of tetrahedral dianions by a hexaaza cryptand receptor

“…In fact, besides an early article by Lehn and Heyer describing the synthesis and anion binding properties of two benzene capped polyammonium cryptands with aliphatic spacers, 7 only one such cryptand has been reported so far but has been explored for its carbohydrate recognition rather than for anion recognition. 8 It was not until very recently, and when our studies were in progress, that an almost identical cryptand was studied as a halide receptor in DMSO-d 6 by 1 H-NMR spectroscopy, although no quantitative binding information was supplied. 9…”