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

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, X-dia-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 X-dia-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 variable-pressure 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.