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

Porous organic cages (POCs) are emerging porous molecular materials with their tunable porosity and solution processability. Beyond the intrinsic pores within individual cage molecules, extrinsic pores generated by intermolecular packing play a critical role in defining the porosity and separation performance of POCs. These packing-derived pores can connect discrete cage cavities, impose size-selective constraints, and create tailored adsorption microenvironments. However, their systematic design and utilization remain underdeveloped, as current synthetic and post-synthetic modification strategies largely focus on intrinsic-pore engineering. In this study, we report an extrinsic pores engineering strategy based on the structural modification of tetrazine-based POCs. By tuning cage shape and peripheral steric hindrance, we precisely modulate frustrated packing to achieve highly selective acetylene uptake. The optimized cage, m-4N-cage, exhibits excellent acetylene/ethylene separation performance in adsorption and breakthrough experiments, comparable to that of the best-performing porous molecular organic materials. In situ single-crystal diffraction analysis reveals that acetylene molecules are selectively adsorbed within the tailored extrinsic pores. This work highlights extrinsic pores as a tunable design element for targeted separations and establishes as a model platform for controlling frustrated packing in molecular crystal engineering.