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 molecular design principle. The scope and magnitude of this attraction are subject to intense debate, however, along with its ability to outweigh competing effects. Here, we describe a system of four tetrahedral M4LR4 cages (M = FeII or ZnII, R = Me or Et), each confining 12 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─at the expense of other driving forces. The observed trends align with the optimization of London dispersion between the confined alkyl groups, predominating over criteria of steric hindrance, strain, solvophobic effects, and metal-ligand bond strength. 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.