Construction and Hierarchical Self-Assembly of Multifunctional Coordination Cages with Triangular Metal–Metal-Bonded Units

Abstract

Herein, a series of face-capped (Tr₂M₃)₄L₄ (Tr = cycloheptatrienyl cationic ring; M = metal; L = organosulfur ligand) tetrahedral cages <b>1</b>-<b>3</b> functionalized with 12 appended crown ether moieties were designed and synthesized. The reversible binding of ammonium cations with peripheral crown ether moieties to adjust internal guest-binding was realized. Combination of a bisammonium linker and cage <b>3</b> led to the formation of a supramolecular gel <b>SPN1</b> via host-guest interactions between the crown ether moieties and ammonium salts. The obtained supramolecular gel exhibited multiple-stimuli responsiveness, injectability, and excellent self-healing properties and could be further developed to a <b>SPN1</b>-based drug delivery system. In addition, the storage modulus of <b>SPN1</b> was 20 times higher than that of the model gel without Pd-Pd bonded blocks, and <b>SPN1</b> had better self-healing properties compared with the latter, demonstrating the importance of such cages in improving mechanical strength without losing the dynamic properties of the material. The cytotoxicity in vitro of the drug-loaded (doxorubicin or methotrexate) <b>SPN1</b> was significantly improved compared to that of free drugs.