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.