Backbone-Bridging Promotes Diversity in Heteroleptic Cages

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Self-sorting of shape-complementary ligands with Pd(II) cations forms heteroleptic cages.
• Diversification of these assemblies is crucial for exploring new structural possibilities.

Purpose of the Study:

• To investigate the impact of covalent backbone bridges on ligand L^A.
• To explore how linker flexibility and solvent/guest effects influence the resulting metallo-supramolecular assemblies.
• To demonstrate control over structural differentiation and complexity in self-assembled cages.

Main Methods:

• Synthesis of modified bis-monodentate ligands (L^A) with varying backbone bridges.
• Self-assembly reactions with Pd(II) cations and complementary ligands (L^B) in different solvents.
• Structural characterization of the resulting metallo-supramolecular cages using X-ray crystallography.

Main Results:

• Introduction of flexible linkers in L^A led to a tetranuclear dimer (D1) in acetonitrile and a trinuclear pseudo-tetrahedron (T1) in DMSO.
• A rigid linker in L^A resulted in a dimer (D2) with a rotated ligand arrangement.
• An anionic guest induced transformation of dimer D2 into a hexanuclear prismatic barrel (P2).

Conclusions:

• Covalent backbone modification of ligands offers a powerful strategy to control metallo-supramolecular assembly.
• Ligand coordination mode, linker flexibility, solvent, and guest interactions are key factors in directing the formation of diverse cage structures.
• This work expands the complexity and tunability of metallo-supramolecular cages for potential applications.