La^III and Zn^II Cooperatively Template a Metal–Organic Capsule

An organic subcomponent was designed with 2-formyl-8-aminoquinoline and triazole-pyridine ends. The relative orientations and geometries of these two ends enabled this subcomponent to assemble together with Zn^II and La^III cations to generate a heterobimetallic tetrahedral capsule. The La^III cations each template three imine bonds that hold together a 3-fold-symmetric metallo-ligand, defining the center of each tetrahedron face. The Zn^II cations occupy the other ends of these <i>C</i>₃ axes, defining the vertices of the tetrahedron. This is the first example where subcomponent self-assembly brought into being the faces of a polyhedron, as opposed to the vertices. Host–guest studies show positively cooperative binding toward ReO₄^–, the encapsulation of which also resulted in the quenching of capsule fluorescence.