Tailoring pore aperture in zirconium-based metal–organic cages for improved CO₂/N₂ separation

Zirconium-based metal–organic cages (Zr-MOCs) are promising candidates for gas separation owing to their exceptional chemical stability and modular structure. In this work, we present the rational design and synthesis of a series of lantern-shaped Zr-MOCs (WSU-1, WSU-2, and WSU-3) using 1,1′-methylenebis(1H-pyrazole-4-carboxylate) (L1), 1,1′-methylenebis(1H-pyrazole-3,5-dimethyl-4-carboxylate) (L1-Me), or their combination. Among them, WSU-3 represents the first single-crystal X-ray diffraction result of a mixed-ligand Zr-MOC. Beyond structural novelty, the studied Zr-MOCs exhibit highly tunable porosity. Specifically, the limited pore aperture size in WSU-2 results in a robust molecular sieving effect for N₂. Its 3.4 Å pore aperture effectively excludes N₂ while maintaining high CO₂ accessibility at 298 K. Consequently, WSU-2 demonstrates superior performance for carbon capture, achieving a CO₂/N₂ selectivity of 45.92 and a CO₂ capacity of 0.47 mmol g^–1 at 15 kPa.