Selective separation of light rare-earth elements by supramolecular encapsulation and precipitation Joseph O'Connell-Danes 1 , Bryne T. Ngwenya 2 , Carole A. Morrison 1 , Jason B. Love 1 1 EaStCHEM School of Chemistry, University of Edinburgh, U.K, 2 School of Geosciences, University of Edinburgh, U.K The Rare Earth (RE) elements are increasingly crucial to modern technologies yet their extraction, separation, and recycling using conventional techniques remain challenging. 1,2 Supramolecular strategies for RE separations are emerging which amplify the limited changes in properties across the series to bias selectivity in extraction or precipitation. 3 Herein, we report a pre-organised triamidoarene platform which, under acidic, biphasic conditions, uniquely and selectively precipitates light REs as hexanitratometalate capsules. The capsules exhibit both intra and intermolecular hydrogen bonds that dictate selectivity, promote precipitation, and facilitate the straightforward release of the RE and recycling of the receptor. This discovery provides a new self-assembly route to metal separations that exploits size and shape complementarity and which has the potential to integrate into conventional processes due to compatibility with acidic metal feed streams. 4
Figure 1. Encapsulation and precipitation of the REs. (a) the tripodal amido-arene L used in this study, (b) the capsular hexanitratometalate complex, [{La(NO 3 ) 6 } (H 3 L 2 )] n 1-La , (c) a schematic of the precipitation of REs by L from a biphasic nitric acid/toluene mixtures and its stripping using a polar protic solvent such as water. References 1. D.S. Sholl, R.P. Lively; Nature, 2016 , 533(7603), 316-316. 2. T. Cheisson, E.J. Schelter, Science, 2019 , 363(6426), 489-493. 3. E.J. Werner, E.M. Biros, Organic Chemistry Frontiers, 2019 , 6(12), 2067-2094 4. J.G. O’Connell-Danes, B.T. Ngwenya, C.A. Morrison, J.B. Love, Nature Communications, in press.
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