Molecular motion in the nanospace of MOFs upon gas adsorption investigated by in situ Raman spectroscopy

Molecular motions taking place in the nanospace of metal-organic frameworks (MOFs) are an interesting research subject, although not yet fully investigated. In this work, we utilized in situ Raman spectroscopy in the ultralow-frequency region to investigate the libration motion (including the rotational motion of phenylene rings) of MOFs, in particular [Cu-2(bdc)(2)(dabco)] (Cu-JAST-1), where bdc = 1,4-benzenedicarboxylate and dabco = 1,4-diazabicyclo[2.2.2]octane. The libration mode of Cu-JAST-1 was found to be significantly suppressed by the adsorption of various guest molecules, such as CO2, Ar, and N-2. In addition, an appreciable correlation between the libration mode and adsorption equilibrium time was identified, which provides useful novel tools in the design of MOFs acting as molecular adsorption and separation materials.

Automated summary

In this study, molecular motions in the nanospace of MOFs were investigated using in situ Raman spectroscopy, particularly focusing on the libration motion of Cu-JAST-1. The results showed that the libration mode of Cu-JAST-1 was suppressed by the adsorption of guest molecules, and a correlation between the libration mode and adsorption equilibrium time was identified. This provides useful insights for designing MOFs as molecular adsorption and separation materials.