Secondary Bracing Ligands Drive Heteroleptic Cuboctahedral Pd Cage Formation.

The structural complexity of self-assembled metal-organic capsules can be increased by incorporating two or more different ligands into a single discrete product. Such complexity can be useful, by enabling larger, less-symmetrical, or more guests to be bound. Here we describe a rational design strategy for the use of subcomponent self-assembly to selectively prepare a heteroleptic cage with a large cavity volume (2631 Å) from simple, commercially available starting materials. Our strategy involves the initial isolation of a tris(iminopyridyl) Pd complex , which reacts with tris(pyridyl)triazine ligand to form a heteroleptic sandwich-like architecture . The tris(iminopyridyl) ligand within serves as a "brace" to control the orientations of the labile coordination sites on the Pd centers. Self-assembly of with additional was thus directed to generate a large Pd heteroleptic cuboctahedron host. This new cuboctahedron was observed to bind multiple polycyclic aromatic hydrocarbon guests simultaneously.