Giant Hysteretic Sorption of CO2 : In Situ Crystallographic Visualization of Guest Binding within a Breathing Framework at 298 K.

A dynamic ZnII -MOF has been shown to exhibit extreme breathing behavior under gas pressure. The very narrow pore form of the activated framework opens up in the presence of carbon dioxide, thus making it a suitable material for CO2 capture. Sorption of CO2 at 298 K and relatively high pressure clearly shows a two-step isotherm with giant hysteresis for the second step. In-situ single-crystal diffraction analysis was carried out under CO2 gas pressure at 298 K using an environmental gas cell in order to visualize the interaction between CO2 and the host framework. The results are well supported by pressure-gradient differential scanning calorimetry (P-DSC) and variable-pressure powder X-ray analysis. Theoretical calculations have been carried out in order to further back up the crystallographic data.