Metal organic frameworks (MOFs) are crystalline materials that contain metal-ions or metal-ion clusters as nodes and organic ligands as linkers to form 1-, 2-, and 3-D structures. In addition to their convenient modular synthesis and chemical tunability, this class of materials has been under intense investigation for gas storage and separation applications due to the discovery of many 3-D frameworks with high internal surface areas. Through careful selection of the ligand and metal, which control pore size / shape and MOF-adsorbate interactions, their uptake properties, such as gas selectivity, can be tuned. Despite these desirable properties there is still a bottleneck in the field associated with the deliberate design of materials for targeted applications. Theoretical efforts focused on the development of structure and property prediction tools could be a means this end; however, experimental validation of the tools is necessary for them to be accurately applied to as-yet-synthesized materials in the future. As such, we have carried out a comprehensive experimental and theoretical study of the CO2 adsorption properties in a well-known series of metal–organic frameworks M2(dobdc) M= Mg, Mn, Fe, Co, Ni, Cu, and Zn). In situ structural studies carried out in tandem with gas adsorption measurements have been used to identify the host–guest interactions that lead to significant differences in isosteric heats of CO2 adsorption. Neutron and X-ray powder diffraction and single crystal X-ray diffraction experiments are used to unveil the site-specific binding properties of CO2 within the materials while systematically varying both the amount of CO2 and the temperature. Density functional theory calculations including van der Waals dispersion quantitatively corroborate and rationalize observations regarding intramolecular CO2 angles and trends in relative geometric properties and heats of adsorption in the M2(dobdc)–CO2 adducts.

Experimental and theoretical approach to the study of CO2 adsorption in an extensive family of metal-organic frameworks

249th National Meeting (2015)

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