Supramolecular Host–Guest System That Realizes Adaptive Selection of the Guest through Ligand Regulation

In host-guest chemistry, preserving the original supramolecular topology while achieving the selective recognition and encapsulation of various guest molecules remains a key challenge. In this study, we successfully designed and synthesized a series of bifunctional pyridine ligands derived from 9,9'-bianthracene, which were then coupled with half-sandwiched Cp*Ir/Rh building blocks to form tetranuclear supramolecular metallacycles. Through precise tuning of the ligands' dimensions and the conjugation areas of the building blocks, we effectively directed the host-guest system within these supramolecular structures. We further explored the spatial conformational factors influencing guest molecule screening. The unique properties of the three bidentate pyridyl ligands significantly affected the intra/intermolecular π-π stacking, CH-π interactions, and hydrogen bonding, which in turn influenced the system's ability to recognize and tolerate different guest molecules. Self-sorting investigations revealed a selective preference for certain ligands and building blocks during macrocyclic formation with no interference from externally imposed guest molecules. These studies also demonstrated the remarkable topological stability of the ligated macrocycles, ensuring high-intensity conformational integrity. The specific structures and behaviors of these supramolecular metallacycles were confirmed by using single-crystal X-ray diffraction, nuclear magnetic resonance (NMR), and mass spectrometry techniques.