Unexpected Self‐Sorting Self‐Assembly Formation of a [4:4] Sulfate:Ligand Cage from a Preorganized Tripodal Urea Ligand

The design and synthesis of tripodal ligands 1 – 3 based upon the N ‐methyl‐1,3,5‐benzenetricarboxamide platform appended with three aryl urea arms is reported. This ligand platform gives rise to highly preorganized structures and is ideally suited for binding SO 4 2− and H 2 PO 4 − ions through multiple hydrogen‐bonding interactions. The solid‐state crystal structures of 1 – 3 with SO 4 2− show the encapsulation of a single anion within a cage structure, whereas the crystal structure of 1 with H 2 PO 4 − showed that two anions are encapsulated. We further demonstrate that ligand 4 , based on the same platform but consisting of two bis‐urea moieties and a single ammonium moiety, also recognizes SO 4 2− to form a self‐assembled capsule with [4:4] SO 4 2− : 4 stoichiometry in which the anions are clustered within a cavity formed by the four ligands. This is the first example of a self‐sorting self‐assembled capsule where four tetrahedrally arranged SO 4 2− ions are embedded within a hydrophobic cavity.