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

An unprecedented bisthianthrene dipyridyl ligand was designed and synthesized for coordination driven self-assembly. The combination of this conformationally dynamic linker with a 90° convergent metal corner exclusively afforded a novel M₂L₂ truncated square-like metallamacrocycle. The single crystal X-ray structure reveals a belt-shaped geometry with a cavity diameter of ca. 13.7 Å. The breathable cavity and electron-rich thianthreno panels enable the highly efficient binding of the fullerenes C₆₀ (K_a = 5.1 × 10⁶ M^-1) and C₇₀ (K_a = 3.7 × 10⁶ M^-1). The encapsulation of C₆₀ is fully confirmed by NMR, mass spectroscopy and single crystal X-ray diffraction analyses. The cyclic voltammograms further reveal that the truncated square is redox active. The strong binding affinity, adaptive complexation, and redox activity of the thianthrene-incorporated metallamacrocycle provide new insights into the design of supramolecular hosts.