Receptors for the recognition and extraction of lithium

We summarize advances in lithium recognition receptors, focusing on their use as active reagents in circular processes such as liquid–liquid extraction, an established industrial process that is advantageous due to its large processing capacity and high selectivity. High-performance systems are required, given the increasing demand for effective separation processes for the recovery of valuable substances from spent lithium-ion batteries or the exploration of brines. Hence, the availability of powerful and highly selective receptors is particularly crucial. This mini-review summarizes the development of active receptors for lithium ion extraction and covers advances in receptors for both lithium ions and lithium salts. It discusses various receptor types, ranging from heteroditopic macrocyclic systems to simple β-diketones. The latter achieve particularly high lithium ion extraction yields in the presence of phosphine oxides such as trioctylphosphine oxide. Structural studies employing 4-phosphorylpyrazolone exhibited diverse coordination modes of lithium and represent clear evidence for the synergistic role of the co-ligand on a molecular level.