Tailoring Pore Aperture in Zirconium-Based Metal–Organic Cages for Improved CO ₂ /N ₂ 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(1 H -pyrazole-4-carboxylate) ( L1 ), 1,1′-methylenebis(1 H -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 N 2 . Its 3.4 Å pore aperture effectively excludes N 2 while maintaining high CO 2 accessibility at 298 K. Consequently, WSU-2 demonstrates superior performance for carbon capture, achieving a CO 2 /N 2 selectivity of 45.92 and a CO 2 capacity of 0.47 mmol g –1 at 15 kPa.