London dispersion governs stereochemistry, stability, and self-sorting in a system of M4L4 cages

London dispersion forces between alkyl groups can give rise to “steric attraction”—a promising design principle in organic chemistry. The scope and magnitude of this attraction are subject to intense debate, however, with few examples known where dispersion is able to outweigh competing effects. Here we describe a system of four tetrahedral M4L(R)4 cages (M=Fe(II) or Zn(II), R=Me or Et), each confining twelve R groups within the cavity. These cages clearly demonstrate how steric attraction can dictate cage stereochemistry and stability—both in solution and in the gas phase—predominating over criteria of steric hinderance, strain, solvophobic effects, and metal-ligand bond strength. Instead, the observed trends align with the optimization of London dispersion between the confined alkyl groups, at the expense of other driving forces. These differences in stability manifested during the self-sorting of a mixture containing two metals and two ligands into cages that feature optimal alkyl alkyl contacts, despite the entropic preference for a statistical mixture. This work thus establishes metal-organic cages as a promising platform to study London dispersion forces.