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

Efficient adsorptive separation of acetylene (C₂H₂) from carbon dioxide (CO₂) or ethylene (C₂H₄) 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 C₂H₂ separation. The intruding cyanide and nitrosyl groups in undulating one-dimensional channels induce negative electrostatic potentials for preferential C₂H₂ recognition instead of open metal sites in traditional Hofmann-type MOFs. As a result, Cu(bpy)NP exhibits a 50/50 C₂H₂/CO₂ selectivity of 47.2, outperforming most rigid MOFs. The dynamic breakthrough experiment demonstrates a 99.9% purity C₂H₄ productivity of 20.57 mmol g^-1 from C₂H₂/C₂H₄ (1/99, v/v) gas-mixture. Meanwhile, C₂H₂ can also be captured and recognized from ternary C₂H₂/CO₂/C₂H₄ (25/25/50, v/v/v) gas-mixture. Furthermore, computational studies and in-situ infrared spectroscopy reveal that the selective C₂H₂ binding arises from the compatible pore electro-environment generated by the electron-rich N and O atoms from nitroprusside anions.