A self-assembled M₂L₂ truncated square and its application as a container for fullerenes

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Synthesis

Background:

• Designing sophisticated supramolecular hosts is crucial for molecular recognition and encapsulation.
• Metallamacrocycles offer tunable structures and properties for host-guest chemistry.
• Thianthrene units can impart unique electronic and structural characteristics to molecular frameworks.

Purpose of the Study:

• To design and synthesize a novel bisthianthrene dipyridyl ligand for coordination-driven self-assembly.
• To construct and characterize a unique M2L2 truncated square-like metallamacrocycle.
• To investigate the host-guest properties, specifically the binding of fullerenes, and the redox activity of the resulting metallamacrocycle.

Main Methods:

• Ligand design and synthesis of bisthianthrene dipyridyl.
• Coordination-driven self-assembly with a 90° metal corner.
• Single crystal X-ray diffraction for structural elucidation.
• Spectroscopic methods (NMR, Mass Spectrometry) for guest encapsulation confirmation.
• Cyclic voltammetry for redox activity analysis.

Main Results:

• Successful synthesis of a conformationally dynamic bisthianthrene dipyridyl ligand.
• Exclusive formation of a M2L2 truncated square-like metallamacrocycle with a belt-shaped geometry and a 13.7 Å cavity.
• Highly efficient binding of C60 (Ka = 5.1 × 10^6 M^-1) and C70 (Ka = 3.7 × 10^6 M^-1) fullerenes due to the breathable cavity and electron-rich thianthrene panels.
• Confirmation of C60 encapsulation through NMR, mass spectrometry, and X-ray diffraction.
• Demonstration of redox activity in the metallamacrocycle.

Conclusions:

• The designed bisthianthrene dipyridyl ligand enables the formation of a novel metallamacrocycle with a large, breathable cavity.
• The metallamacrocycle exhibits strong binding affinity and adaptive complexation for fullerenes.
• The thianthrene-incorporated metallamacrocycle's redox activity provides new avenues for supramolecular host design.