Elucidation of the Structural Origins and Contrasting Guest-Host Interactions in CO2 -Loaded CdSDB and PbSDB Metal-Organic Frameworks at High Pressures.

PbSDB and CdSDB (SDB=4,4'-sulfonyldibenzoate) are two structurally related SDB-based metal-organic frameworks (MOFs) that demonstrate promising potential for selective CO2 adsorption capabilities. The structural stabilities and guest-host interactions between CO2 and PbSDB or CdSDB frameworks at high pressures up to 13 GPa in situ were comparatively investigated by Raman spectroscopy, FTIR spectroscopy, and synchrotron X-ray diffraction. Although both empty frameworks exhibited high chemical stabilities upon compression, they show different pressure-induced modifications in crystallinity. This difference can be attributed to their different coordination topologies that result in near isotropic contraction of unit cells for the CdSDB framework but anisotropic for the PbSDB framework. Furthermore, the CO2 -loaded PbSDB and CdSDB frameworks at high pressures show strongly contrasting guest-host interactions in terms of the pressure-regulated CO2 adsorption sites. In both frameworks, pressure can highly efficiently promote the formation of new CO2 adsorption sites and the enhancement of guest-host interactions. In the CO2 -loaded PbSDB framework, in particular, the peculiar pressure-tuned CO2 population was observed preferentially on one of the two adsorption sites in response to external compression. These unique guest-host interaction behaviors can also be unambiguously correlated to their different topological origins. These findings for the PbSDB and CdSDB frameworks provide in-depth understanding of the structure-property relationship, which is of fundamental importance for CO2 storage application in SDB-based MOFs.