Double-Accessible Open Metal Sites in Metal–Organic Frameworks with Suitable Pore Size for Efficient Xe/Kr Separation

The separation of a Xe/Kr mixture is an industrially important but challenging process due to their inherent inert nature and similar atomic sizes. Porous materials containing open metal sites have been extensively proved to be an effective strategy for the Xe/Kr capture and separation. However, conventional materials with single open metal sites display the limitations of gas uptake at low pressure and separation selectivity of a Xe/Kr mixture. Herein M(pz)[Ni(CN)4], simplify as MpzNi (M = Co, Ni, pz = pyrazine), with a suitable pore size and double accessible open metal sites, can synergistically afford strong interactions for Xe capture from a Xe/Kr mixture. CopzNi exhibits high uptake of 2.49 mmol/g at 20 kPa and a remarkable dynamic adsorption amount of Xe (2.35 mmol/g), outperforming most of previously reported materials. Density functional theory calculations further reveal that the excellent separation performance is driven by the compact pore size and cooperative interactions afforded by the double accessible open metal sites.