Highly Efficient Separation of Hexane Isomers by Rigid-Flexible Pyrazine-Pillar Ultramicroporous Metal-Organic Framework

Separating linear, monobranch, and dibranch alkanes is a pivotal process in the petrochemical industry. Herein, we present an ultramicroporous metal-organic framework (MOF) with a rigid-flexible structure. Single-component adsorption isotherms demonstrate that this MOF exhibited high capacities for hexane (nHEX) and 3-methylpentane (3MP), whereas excluding 2,2-dimethylbutane (22DMB), resulting in remarkable uptake ratios for nHEX/22DMB (19.2) and 3MP/22DMB (12.6) at 303 K, surpassing those of most reported MOFs. Breakthrough results with the nHEX/3MP/22DMB ternary mixture further validate its excellent separation performance and good reusability. Single-crystal structure data of MOF adsorbing gas molecules reveal that the outstanding performance can be ascribed to its suitable pore size and guest-induced flexibility, with an adaptive backbone triggered by nHEX and 3MP, leading to strong affinities for these molecules and precisely locating their positions within the framework.