Self-Assembly, Structural Transformation, and Guest-Binding Properties of Supramolecular Assemblies with Triangular Metal–Metal Bonded Units

The properties of supramolecular structures are highly dependent on their metal-centered building blocks and organic linkers, thus the search for novel systems will lead to new functions and applications for these unique assemblies. Here, two discrete triangular trimetallic sandwich building blocks were developed to construct supramolecular assemblies through coordination-driven self-assembly with organosulfur ligands. A series of tubelike (Tr₂Pd₃)₄L₆ assemblies (Tr = cycloheptatrienyl ring) were obtained from a discrete triangular tripalladium sandwich complex with bifunctional organosulfur ligands. By replacing the metal centers of the platinum analogue, the self-assembly process resulted in the clean formation of (Tr₂Pt₃)₂L₃ triple helicates instead of tubelike species. The trimetallic sandwich building blocks were also shown to form face-capped (Tr₂M₃)₄L₄ (M = Pd or Pt) tetrahedral cages when trifunctional organosulfur ligands were used. The supramolecular assemblies were comprehensively analyzed by X-ray crystallography. A metal-cluster-induced structural transformation between (Tr₂Pd₃)₄L₄ tubes and (Tr₂Pt₃)₂L₃ triple helicates was observed. Furthermore, the face-capped (Tr₂Pd₃)₄L₄ cage possesses a tetrahedral cavity allowing the encapsulation of a series of guests.