Ethane/Ethylene Separations in Flexible Diamondoid Coordination Networks via an Ethane-Induced Gate-Opening Mechanism

Abstract

Separating ethane (C 2 H 6 ) from ethylene (C 2 H 4 ) is an essential and energy-intensive process in the chemical industry. Here, we report two flexible diamondoid coordination networks, Xdia-1-Ni and X-dia-1-Ni 0.89 Co 0.11 , that exhibit gate-opening between narrow-pore (NP) and large-pore (LP) phases for C 2 H 6 , but not for C 2 H 4 . X-dia-1-Ni 0.89 Co 0.11 thereby exhibited a type F−IV isotherm at 273 K with no C 2 H 6 uptake and a high uptake (111 cm 3 g −1 , 1 atm) for the NP and LP phases, respectively. Conversely, the LP phase exhibited a low uptake of C 2 H 4 (12.2 cm 3 g −1 ). This C 2 H 6 /C 2 H 4 uptake ratio of 9.1 for Xdia-1-Ni 0.89 Co 0.11 far surpassed those of previously reported physisorbents, many of which are C 2 H 4 -selective. In situ variablepressure X-ray diffraction and modeling studies provided insight into the abrupt C 2 H 6 -induced structural NP to LP transformation. The promise of pure gas isotherms and, more generally, flexible coordination networks for gas separations was validated by dynamic breakthrough studies, which afforded high-purity (99.9%) C 2 H 4 in one step.

Solvent-Driven Switchable Structural Deformations in a Flexible Metal–Organic Framework with Pyrrolo-Pyrrole–Based Linker

“…Flexible metal–organic frameworks (FMOFs), due to the combination of highly ordered framework and dynamic structural nature, have captivated researchers in the past decade. − This trend is a corollary of their dynamic responses in a tunable or adaptive fashion to external stimuli, making this type of material particularly applicable in gas storage/separation, − sensing, − and catalysis. − Among various external stimuli such as light, − pressure, − and temperature, − guest molecules are the most common triggers for driving structural transformations in FMOFs. − Solvents as guest may influence and regulate the crystal growth, assembly, framework and topology, and even the final properties of MOFs. , Although the interaction between solvents and coordination motifs is weak, it can still readily affect the linker conformations and coordination geometries around metal centers in a switchable manner (present or absent), leading to substantial changes in FMOFs. − One primary example that illustrates the solvent-induced structural transformations (breathing behavior) in MOFs is MIL-53 series. , Although a large number of FMOFs have been reported in recent years, − it is still of fundamental importance to identify the host–guest interactions and establish the mechanism and forces responsible for the flexibility of MOFs. Therefore, guest-induced dynamic structural transformations, especially single-crystal-to- single-crystal (SCSC) transformations, for probing the correlation between applied stimuli and dynamic structures are quite appealing. − …”