Metal-organic frameworks are porous materials with promising applications in gas sorption, capture, storage and purification. Recent work has shown that the presence of highly polarizing, unsaturated metal coordination centers (Lewis acid open metal sites) on the internal surface of framework pores increases the surface packing density of adsorbates, induces selectivity and provides a mechanism to achieve charge transfer on the internal surface. X-ray and neutron powder diffraction were shown to be excellent methods to study the interactions of gas molecules with the pore surface. In situ diffraction studies were performed with different probe molecules, including CO2, H2, D2, Xe, and Kr, in metal-organic frameworks with single[1] or double exposed metal sites.[2] Furthermore, it was shown that complementary structural information for the gas-framework interactions can be obtained by in situ IR spectroscopy, which is particularly useful for probing specific sites at poorly crystalline materials.[3] Another strategy to design superior storage materials utilizes flexible metal-organic frameworks. These materials collapse under reduced gas pressure and step-vise expand under increasing pressure. In the collapsed form they are virtually nonporous, whereas when expanded they exhibit high gas storage capacity. In situ X-ray powder diffraction was proven to be very useful technique to follow and explain these structural transformations under variable temperature and methane or nitrogen pressure, and to inform the design of new flexible metal-organic frameworks.[4]

In Situ diffraction and spectroscopic studies of metal-organic frameworks under variable temperature and gas pressure

253rd National Meeting (2017)

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