Enantiopure [Cs$^+$/Xe$\subset$Cryptophane]$\subset$Fe$^{II}$$_4$L$_4$ Hierarchical Superstructures

Abstract : Hierarchically nested hosts offer new opportunities to control the guest binding of the inner host, functionalize the cavity of the outer host, and investigate communication between different layers. Here we report a self-assembled triazatruxene-based Fe$^{II}$$_4$L$_4$ capsule, which was able to encapsulate a covalent cage, cryptophane-111 (CRY). The resulting cage-in-cage complex was capable of accommodating a cesium cation or xenon atom with altered guest binding behavior compared to the CRY alone. A crystal structure of the Russian doll complex [Cs$^+$/Xe$\subset$CRY]$\subset$Fe$^{II}$$_4$L$_4$ unambiguously demonstrated the unusual encapsulation of a cation within a capsule bearing a 8+ charge. Moreover, the binding of enantiopure CRY occurred with high enantioselectivity (530-fold) between the two enantiomers of the tetrahedron. This discrimination resulted in stereochemical information transfer from the inner covalent cage to the outer self-assembled capsule, leading to the formation of enantiopure [guest$\subset$cage]$\subset$cage complexes. The stereochemistry of the tetrahedron persisted even after displacement of CRY with an achiral guest.