Metal−Organic Framework with Constrained Flexibility for Benchmark Separation of Hexane Isomers
Kuishan Wen, Jingyi Zhou, Tian Ke, Jinjian Li, Yuanyuan Jin, Qingbo Zhang, Zhiguo Zhang, Zongbi Bao, Qilong Ren, Qiwei Yang, Qiwei Yang
Abstract
Abstract Flexible metal−organic frameworks (MOFs) are promising candidates for adsorptive separations, but achieving a balance among flexibility, adsorption capacity, and selectivity remains challenging. Herein, we report a novel flexible MOF, Ni(bhdc)(ted) 0.5 (ZUL−C6), incorporating hybrid three‐dimensional alkane‐bridged ligands, which realizes high‐capacity molecular sieving for hexane isomer separation ‐ a critical process in the petroleum industry. The alkyl‐rich, confined pore system within the ZUL−C6 framework facilitated a strong affinity for n‐hexane and 3‐methylpentane. However, the narrow pore size and the constrained flexibility limited the uptake of 2,2‐dimethylbutane (<4.0 mg/g), accompanied by a high gate‐opening pressure. The gating behavior was elucidated by guest‐loaded single‐crystal (SC) X‐ray diffraction and density functional theory (DFT) simulations, which revealed a unique SC to SC transformation driven by the non‐centrosymmetric rotation of the 3D bhdc linker and distortion of the metal cluster and pillar units, along with a high deformation energy barrier. As a result, ZUL−C6 exhibited not only significantly higher uptake and selectivity than the industrially used 5 A molecular sieve, but also the record‐high nHEX/3MP breakthrough uptake (92.8/73.9 mg/g) and unprecedented 22DMB producing time (309.2 min/g, corresponding to the productivity of 770 mmol/kg and yield of 92.8 %) among reported MOFs.