Abstract
Selective anion extraction is useful for the recovery and purification of valuable chemicals, and in the removal of pollutants from the environment. Here we report that FeII 4L4 cage 1 is able to extract an equimolar amount of ReO4 −, a high‐value anion and a nonradioactive surrogate of TcO4 −, from water into nitromethane. Importantly, the extraction was efficiently performed even in the presence of 10 other common anions in water, highlighting the high selectivity of 1 for ReO4 −. The extracted guest could be released into water as the cage disassembled in ethyl acetate, and then 1 could be recycled by switching the solvent to acetonitrile. The versatile solubility of the cage also enabled complete extraction of ReO4 − (as the tetrabutylammonium salt) from an organic phase into water by using the sulfate salt of 1 as the extractant.
Highlights
Selective anion extraction is useful for the recovery and purification of valuable chemicals, and in the removal of pollutants from the environment
Because of its similar structure and almost identical charge density, perrhenate is used as a nonradioactive surrogate for pertechnetate (99TcO4À),[6] which is an important radiopharmaceutical and one of the most problematic radioactive ions in nuclear waste.[7]
Significant advances have been made in designing sorbent materials for removing ReO4À/ TcO4À from aqueous solution by liquid–solid extraction.[7,8]
Summary
Selective anion extraction is useful for the recovery and purification of valuable chemicals, and in the removal of pollutants from the environment. Most supramolecular anion extractants have been robust covalent receptors[12] as opposed to coordination cages.[13] Such extractants must be stable in the presence of both water and organic solvents,[14] properties that are easier to engineer for covalent systems. We tested the stability of the cage, as Tf2NÀ& 1·[BArF]11 (Tf = CF3SO2), in ethyl acetate and nitromethane, both of which are water-immiscible organic solvents suitable for liquid–liquid extraction experiments.
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