One Coordination Cage, Many Pathways: Multiple Stimuli Drive Reversible Transformations

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Self-assembly of coordination cages is a key strategy in supramolecular chemistry.
• Designing cages with tunable properties and responsiveness is an ongoing challenge.
• Triazatruxene ligands offer a rigid, planar platform for constructing complex architectures.

Purpose of the Study:

• To construct a novel trigonal prismatic coordination cage with a large cavity.
• To investigate the stimulus-responsive structural transformations of the cage.
• To explore the cage's capabilities in guest encapsulation and interlocked structures.

Main Methods:

• Self-association of a bis-(rhodium) complex with a triazatruxene ligand.
• Manipulation of external stimuli: cage concentration, guest identity, and pH.
• Characterization using NMR spectroscopy, mass spectrometry, theoretical calculations, and X-ray diffraction.

Main Results:

• Formation of a trigonal prismatic coordination cage with a large internal cavity.
• Demonstration of four interconvertible stable structures: monomeric cage, two host-guest complexes, and a cage dimer.
• Observation of selective double guest encapsulation, stimulus-controlled catenation, and pH-triggered guest exchange.

Conclusions:

• The developed coordination cage exhibits remarkable structural versatility and responsiveness.
• The cage enables on-demand formation of discrete structures and mechanically interlocked architectures.
• This work presents a unique molecular building block with potential applications in molecular machines and sensing.