Metal–organic frameworks (MOFs) are crystalline, porous materials composed of metal centers and organic linkers. They have applications, e.g., in catalysis or gas separation. Acetylene (C₂H₂) gas, for example, serves as an important feedstock in the chemical industry. It often needs to be separated from impurities such as ethylene or carbon dioxide. However, these compounds can be difficult to separate using porous materials due to their similar sizes and physical properties. Tailoring the properties of MOFs could help to provide good separation efficiencies for the purification of acetylene.

Ying Wang, Quan-Guo Zhai, Shaanxi Normal University, Xi’an, China, and colleagues have combined open metal sites (Fe or Sc) and Lewis basic sites in robust MOFs that can be used for C₂H₂ purification. The team prepared two isostructural MOFs, called SNNU-37(Fe/Sc), which consist of amide-functionalized tricarboxylate linkers and trinuclear metal clusters of the type [M₃O(COO)₆]. The MOFs were prepared from FeCl₂·4 H₂O or Sc(NO₃)₃·6 H₂O and 5-(4-carboxybenzoylamino)isophthalic acid.

According to the researchers, the open Fe/Sc sites and the amide groups on the pore surfaces of the MOFs work in tandem to improve the acetylene adsorption performance. The acetylene adsorption capacities of the materials are much higher than those for ethylene and carbon dioxide. SNNU-37(Fe), in particular, might be able to effectively separate C₂H₂/C₂H₄ and C₂H₂/CO₂ under ambient conditions.

• Amide-Functionalized Metal–Organic Frameworks Coupled with Open Fe/Sc Sites for Efficient Acetylene Purification,
  Shu-Cong Fan, Yun-Tong Li, Ying Wang, Jia-Wen Wang, Ying-Ying Xue, Hai-Peng Li, Shu-Ni Li, Quan-Guo Zhai,
  Inorg. Chem. 2021.
  https://doi.org/10.1021/acs.inorgchem.1c03044