Negative electrostatic potentials in a Hofmann-type metal-organic framework for efficient acetylene separation

Efficient adsorptive separation of acetylene (C(2)H(2)) from carbon dioxide (CO(2)) or ethylene (C(2)H(4)) is industrially important but challenging due to the identical dynamic diameter or the trace amount. Here we show an electrostatic potential compatible strategy in a nitroprusside-based Hofmann-type metal-organic framework, Cu(bpy)NP (NP = nitroprusside, bpy = 4,4’-bipyridine), for efficient C(2)H(2) separation. The intruding cyanide and nitrosyl groups in undulating one-dimensional channels induce negative electrostatic potentials for preferential C(2)H(2) recognition instead of open metal sites in traditional Hofmann-type MOFs. As a result, Cu(bpy)NP exhibits a 50/50 C(2)H(2)/CO(2) selectivity of 47.2, outperforming most rigid MOFs. The dynamic breakthrough experiment demonstrates a 99.9% purity C(2)H(4) productivity of 20.57 mmol g(−1) from C(2)H(2)/C(2)H(4) (1/99, v/v) gas-mixture. Meanwhile, C(2)H(2) can also be captured and recognized from ternary C(2)H(2)/CO(2)/C(2)H(4) (25/25/50, v/v/v) gas-mixture. Furthermore, computational studies and in-situ infrared spectroscopy reveal that the selective C(2)H(2) binding arises from the compatible pore electro-environment generated by the electron-rich N and O atoms from nitroprusside anions.