A Hexadecacationic Metal–Organic Cage for Anchoring Sulfonates: High‐Order Binding of Di‐ and Trisulfonates and High‐Performance Removal of Perfluorosulfonates from Water

Developing synthetic hosts capable of binding sulfonate anions or sequestering perfluorosulfonates is highly important. In this work, the self-assembly of a tripyridinium-tricarboxylate ligand with Cp₂ZrCl₂ (Cp = η⁵-C₅H₅) is reported, yielding a highly cationic tetrahedral cage (1) engineered with acidic C-H protons. The hexadecacationic cage binds a variety of sulfonate anions with unprecedented charge-discriminative phenomena: the cage binds monosulfonates in fast exchange on the NMR timescale, while di- and multisulfonates exhibit slow-exchange binding. In particular, high-capacity complexation of di- and trisulfonates by 1 is achieved, with the pronounced case of 1 accommodating three dianions. Molecular modeling suggests the existence of a "Y"-shaped binding pocket on each edge of tetrahedron 1 (six in total), with each pocket capable of anchoring a guest bearing at least two sulfonate headgroups through electrostatic and hydrogen bonding interactions. Further investigations demonstrate that 1 in solid state is an exceptional adsorbent for perfluorooctane sulfonate (PFOS), with a maximum adsorption capacity of up to 1603 mg g^-1 positioning it among the top PFOS adsorbents. Moreover, cage 1 exhibits rapid kinetics, high selectivity, and long-life cycles in PFOS removal, and also effectively adsorbs shorter perfluorosulfonates.