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.