Solid-State Gas Adsorption Studies with Discrete Palladium(II) [Pd₂ (L)₄ ]⁴⁺ Cages

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Chemical Engineering

Background:

• Metallosupramolecular architectures offer tunable properties for gas sorption.
• Discrete metallocage exploitation for gas binding is an emerging field, distinct from extended metal-organic frameworks.
• The development of efficient carbon dioxide (CO2) capture systems is critical.

Purpose of the Study:

• To investigate the solid-state gas adsorption properties of novel [Pd2(L)4]4+ coordination cages.
• To evaluate the CO2 uptake capacity and binding characteristics of these metallocages.
• To explore the potential of discrete cages for CO2 capture applications.

Main Methods:

• Synthesis and characterization of [Pd2(L)4]4+ coordination cages with variants of 2,6-bis(pyridin-3-ylethynyl)pyridine.
• Solid-state gas adsorption measurements for nitrogen (N2) and carbon dioxide (CO2).
• Density Functional Theory (DFT) calculations to model CO2 binding interactions and energetics.

Main Results:

• The coordination cages exhibited minimal interaction with dinitrogen gas.
• Significant reversible CO2 sorption was observed, with the best performing cage sorbing 1.4 mol CO2/mol cage at 298 K and 2.3 mol CO2/mol cage at 258 K (1 bar).
• Calculated binding enthalpies ranged from 25-35 kJ/mol, consistent with DFT-calculated interaction energies of 23-28 kJ/mol.

Conclusions:

• The investigated [Pd2(L)4]4+ coordination cages demonstrate effective CO2 sorption capabilities.
• DFT analysis suggests hydrogen bonding between CO2 and cage components dictates the binding mode.
• These findings highlight the potential of discrete metallocages as a platform for targeted gas capture.