Selective scandium ion capture via coordination templating in a covalent organic framework

The use of coordination complexes as building units within covalent organic frameworks (COFs) has significant potential to diversify the structures and properties of this class of materials. Here, we present a synergistic coordination and reticular chemistry approach to the design of a series of crystalline scandium–covalent organic frameworks (Sc–COFs), featuring tunable levels of metal incorporation. Removal of scandium from the material with the highest metal content results in a metal-imprinted COF (MICOF) that exhibits high affinity and capacity for Sc3+ ions in acidic environments and in the presence of competing metal ions. In particular, the selectivity of this MICOF for Sc3+ over common impurity ions such as La3+ and Fe3+ surpasses that of all reported scandium adsorbents. Importantly, analogous materials can be prepared starting from earth-abundant transition metals, highlighting the versatility of this approach for the development of tailor-made metal–COFs and MICOFs for applications involving selective metal ion capture.