Engineering Frustrated Packing of Porous Organic Cages for Precision Acetylene-Ethylene Separation

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Chemical Engineering

Background:

• Porous organic cages (POCs) are advanced molecular materials known for tunable porosity and solution processability.
• Extrinsic pores, formed by intermolecular packing in POCs, significantly influence overall porosity and separation capabilities.
• Current research predominantly focuses on intrinsic pore engineering, leaving extrinsic pore design underdeveloped.

Purpose of the Study:

• To develop a novel extrinsic pore engineering strategy for tetrazine-based porous organic cages.
• To precisely control frustrated packing through cage shape and steric hindrance modifications.
• To achieve highly selective acetylene uptake and separation from ethylene.

Main Methods:

• Structural modification of tetrazine-based porous organic cages.
• Tuning cage shape and peripheral steric hindrance to modulate intermolecular packing.
• In situ single-crystal X-ray diffraction analysis to elucidate adsorption mechanisms.

Main Results:

• The optimized cage, m-4N-cage, demonstrated highly selective acetylene uptake.
• Achieved excellent acetylene/ethylene separation performance in adsorption and breakthrough experiments.
• Acetylene molecules were observed to selectively adsorb within the engineered extrinsic pores.

Conclusions:

• Extrinsic pores represent a tunable and effective design element for targeted molecular separations.
• The developed strategy provides a model platform for controlling frustrated packing in molecular crystal engineering.
• This approach enables the design of high-performance porous materials for challenging gas separations.