Rediscovering Sodium Ionophores as Selective Agents for Lithium Recognition and Extraction

Conventional brine evaporation leads to substantial lithium losses through the formation of lithium-containing solid precipitates that accumulate as salt stockpiles. Increasing global demand for lithium calls for selective and scalable extraction strategies for such solid materials. Solid-liquid extraction (SLE) enables direct processing of lithium-bearing solids without prior dissolution of the inorganic matrix; however, suitable molecular extractants are scarce and often synthetically complex. Here, we show that long-known sodium-selective ionophores display a clear preference for lithium in solution and function as lithium-selective extractants under SLE conditions. Hosts 1a-h are based on a modular scaffold accessible from catechol and N,N-disubstituted haloacetamides and are readily prepared on a multigram scale (up to 58 g per batch). Lithium recognition proceeds through a hydration-assisted binding mode, in which Li⁺ is coordinated by water, ether, and carbonyl oxygen donors. This enables effective transfer of hydrated lithium salts, as supported by ¹H and ⁷Li NMR spectroscopy, ICP-MS, colorimetric analysis, DFT calculations, and x-ray crystallography. Under semi-preparative SLE conditions, nearly all available LiCl is recovered from a ∼100 g multicomponent salt mixture, affording >95% LiCl purity with Li/Na, Li/K, and Li/Mg selectivities above 3000.