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 butchallenging process due to their inherent inert nature and similar atomic sizes. Porousmaterials containing open metal sites have been extensively proved to be an effectivestrategy for the Xe/Kr capture and separation. However, conventional materials withsingle open metal sites display the limitations of gas uptake at low pressure andseparation 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 metalsites, 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 dynamicadsorption amount of Xe (2.35 mmol/g), outperforming most of previously reportedmaterials. Density functional theory calculations further reveal that the excellentseparation performance is driven by the compact pore size and cooperative interactions afforded by the double accessible open metal sites.