Understanding the interactions between the bis(trifluoromethylsulfonyl)imide anion and absorbed CO(2) using X-ray diffraction analysis of a soft crystal surrogate

The selective carbon dioxide (CO(2)) absorption properties of ionic liquids (ILs) are highly pertinent to the development of methods to capture CO(2). Although it has been reported that fluorinated components give ILs enhanced CO(2) solubilities, it has been challenging to gain a deep understanding of the interactions occurring between ILs and CO(2). In this investigation, we have utilized the soft crystalline material [Cu(NTf(2))(2)(bpp)(2)] (NTf(2)(‒) = bis(trifluoromethylsulfonyl)imide, bpp = 1,3-bis-(4-pyridyl)propane) as a surrogate for single-crystal X-ray diffraction analysis to visualize interactions occurring between CO(2) and NTf(2)(‒), the fluorinated IL component that is responsible for high CO(2) solubility. Analysis of the structure of a CO(2)-loaded crystal reveals that CO(2) interacts with both fluorine and oxygen atoms of NTf(2)(‒) anions in a trans rather than cis conformation about the S–N bond. Theoretical analysis of the structure of the CO(2)-loaded crystal indicates that dispersion and electrostatic interactions exist between CO(2) and the framework. The overall results provide important insight into understanding and improving the CO(2) absorption properties of ILs.