Synergistic Nitrogen Binding Sites in a Metal‐Organic Framework for Efficient N₂/O₂ Separation

Porous materials with d 3 electronic configuration open metal sites have been proved to be effective adsorbents for N 2 capture and N 2 /O 2 separation. However, the reported materials remain challenging to address the trade‐off between adsorption capacity and selectivity. Herein, we report a robust MOF, MIL‐102Cr, that features two binding sites, can synergistically afford strong interactions for N 2 capture. The synergistic adsorption site exhibits a benchmark Q st of 45.0 kJ mol −1 for N 2 among the Cr‐based MOFs, a record‐high volumetric N 2 uptake (31.38 cm 3 cm −3 ), and highest N 2 /O 2 selectivity (13.11) at 298 K and 1.0 bar. Breakthrough experiments reveal that MIL‐102Cr can efficiently capture N 2 from a 79/21 N 2 /O 2 mixture, providing a record 99.99 % pure O 2 productivity of 0.75 mmol g −1 . In situ infrared spectroscopy and computational modelling studies revealed that a synergistic adsorption effect by open Cr(III) and fluorine sites was accountable for the strong interactions between the MOF and N 2 .