An Operationally Simple Method for Separating the Rare‐Earth Elements Neodymium and Dysprosium

Rare‐earth metals are critical components of electronic materials and permanent magnets. Recycling of consumer materials is a promising new source of rare earths. To incentivize recycling there is a clear need for simple methods for targeted separations of mixtures of rare‐earth metal salts. Metal complexes of a tripodal nitroxide ligand [{(2‐tBuNO)C6H4CH2}3N]3− (TriNOx3−), feature a size‐sensitive aperture formed of its three η2‐(N,O) ligand arms. Exposure of metal cations in the aperture induces a self‐associative equilibrium comprising [M(TriNOx)thf]/ [M(TriNOx)]2 (M=rare‐earth metal). Differences in the equilibrium constants (Keq) for early and late metals enables simple Nd/Dy separations through leaching with a separation ratio SNd/Dy=359.