Enantiopure [Cs⁺/Xe⊂Cryptophane]⊂Fe^II₄L₄ Hierarchical Superstructures.

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Chemical Crystallography

Background:

• Hierarchically nested hosts enable precise control over guest interactions within inner cavities.
• Self-assembled capsules offer tunable platforms for complex molecular architectures.
• Investigating inter-layer communication in multi-component systems is crucial for advanced functional materials.

Purpose of the Study:

• To construct and characterize a novel cage-in-cage supramolecular complex.
• To explore the guest binding properties and stereochemical behavior of the hierarchical system.
• To demonstrate stereochemical information transfer from an inner covalent cage to an outer self-assembled capsule.

Main Methods:

• Self-assembly of a triazatruxene-based Fe(II)4L4 capsule.
• Encapsulation of cryptophane-111 (CRY) within the Fe(II)4L4 capsule.
• X-ray crystallography to determine the structure of the Russian doll complex.
• Binding studies with cesium cations and xenon atoms.
• Enantioselective binding experiments with enantiopure CRY.

Main Results:

• A self-assembled Fe(II)4L4 capsule successfully encapsulated the covalent cryptophane-111 (CRY) cage.
• The resulting cage-in-cage complex exhibited altered binding affinities for guests like Cs+ and Xe compared to CRY alone.
• X-ray crystallography confirmed the encapsulation of Cs+ within the [CRY]⊂Fe(II)4L4 complex, revealing an unusual 8+ charge on the outer capsule.
• High enantioselectivity (530-fold) was observed in the binding of enantiopure CRY to the tetrahedron.
• Stereochemical information transfer occurred, leading to enantiopure [guest⊂CRY]⊂Fe(II)4L4 complexes, with stereochemistry persisting even after guest exchange.

Conclusions:

• The Fe(II)4L4 capsule serves as an effective host for the covalent CRY cage, creating a functional hierarchical system.
• The cage-in-cage architecture allows for modulated guest binding and demonstrates the transfer of stereochemical information.
• This work provides a new platform for designing sophisticated supramolecular systems with applications in molecular recognition and sensing.