Tunable Half-Sandwich Iridium Coordination Cages for PAH Guest Encapsulation

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Rational design of molecular cages requires precise control over confinement dimensions.
• Coordination cages offer versatile platforms for molecular recognition and encapsulation.
• Iridium complexes are increasingly utilized in constructing sophisticated supramolecular architectures.

Purpose of the Study:

• To synthesize novel iridium coordination cages with systematically tunable cavity sizes.
• To investigate the binding capabilities of these cages towards polycyclic aromatic hydrocarbons (PAHs).
• To explore the relationship between cage size, shape, and guest binding affinity.

Main Methods:

• Synthesis and characterization of three new iridium coordination cages.
• Spectroscopic techniques including NMR, DOSY, HR-ESI-MS, and SCXRD for structural elucidation.
• Density functional theory (DFT) simulations for analyzing cage structure and guest binding.
• Host-guest titration experiments to determine binding constants.

Main Results:

• Systematic expansion of ligands resulted in structurally analogous cages with tunable cavity dimensions.
• The π-systems of the ligands facilitated the binding of various PAHs, including Benzo[a]pyrene.
• A 1:3 binding stoichiometry between the cages and pyrene was confirmed through NMR and DFT calculations.
• Binding constants decreased with increasing cage size, aligning with Rebek's rule.

Conclusions:

• Tunable iridium coordination cages were successfully synthesized, offering control over cavity properties.
• These cages demonstrate potential for selective binding of PAHs, relevant to environmental and toxicological studies.
• The study provides experimental evidence supporting theoretical predictions on cage-guest interactions and size-dependent binding.