Ligand Side-Chains Control the Formation of an M₈L₄ Molecular Barrel: Unveiling Selective Encapsulation and...

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Steric factors are crucial in biomolecular self-assembly.
• Coordination-driven self-assembly offers precise control over molecular architecture.
• Designing functional supramolecular cages requires understanding ligand-metal interactions and steric influences.

Purpose of the Study:

• To investigate the role of steric factors in the self-assembly of a cationic M₈L₄ barrel.
• To synthesize and characterize a sterically reinforced ligand (L) for self-assembly.
• To evaluate the selective encapsulation and separation capabilities of the resulting supramolecular barrel (MB1) for polycyclic aromatic hydrocarbons (PAHs).

Main Methods:

• Synthesis of a flexible tetrapyridylbiphenyl ligand (L) functionalized with ethoxy groups.
• Coordination-driven self-assembly of the ligand (L) with cis-Pd(en)(NO₃)₂ to form the M₈L₄ barrel (MB1).
• Single-crystal X-ray diffraction analysis to determine the structure of MB1.
• Spectroscopic and binding studies to assess MB1's selectivity and affinity for PAHs in aqueous solution.

Main Results:

• A unique cationic M₈L₄ barrel (MB1) was successfully assembled using a sterically reinforced ligand.
• Structural analysis revealed controlled conformational flexibility of the ethoxy groups within the MB1 cavity.
• MB1 demonstrated high selectivity for encapsulating naphthalene and phenanthrene from aqueous PAH mixtures.
• MB1 exhibited efficient sequential extraction and separation of naphthalene and phenanthrene, outperforming other M₈L₄ barrels.

Conclusions:

• Steric reinforcement in ligands can precisely control supramolecular self-assembly and cavity properties.
• The MB1 barrel serves as an effective molecular separation flask for hazardous PAHs in aqueous environments.
• MB1 offers a reusable and selective platform for challenging PAH separation and extraction processes.