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

Porous materials with d₃ electronic configuration open metal sites have been proved to be effective adsorbents for N₂ capture and N₂ /O₂ 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 N₂ capture. The synergistic adsorption site exhibits a benchmark Q_st of 45.0 kJ mol^-1 for N₂ among the Cr-based MOFs, a record-high volumetric N₂ uptake (31.38 cm³ cm^-3 ), and highest N₂ /O₂ selectivity (13.11) at 298 K and 1.0 bar. Breakthrough experiments reveal that MIL-102Cr can efficiently capture N₂ from a 79/21 N₂ /O₂ mixture, providing a record 99.99 % pure O₂ 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 N₂ .