Metal-organic frameworks (MOFs) are currently among the most promising materials for gas separation applications such as carbon capture. We explore the local electronic signatures of molecular adsorption at coordinatively unsaturated binding sites in the metal-organic framework Mg-MOF-74 using X-ray spectroscopy and first principles calculations. In situ measurements at the Mg K-edge reveal distinct pre-edge absorption features associated with the unique, open coordination of the Mg sites. These spectral features are suppressed upon adsorption of CO2 and N,N'-dimethylformamide.  Density functional theory shows that these spectral changes arise from modifications of local symmetry around the Mg sites upon gas uptake and are strongly dependent on the metal-adsorbate binding strength. Similar sensitivity to local symmetry is expected for any open metal site, making X-ray spectroscopy an ideal tool for examining adsorption in such MOFs. We also present in situ measurements of the expanded, functionalized analogue mmen-Mg2(dobpdc), in which amines have been appended to the metal sites. This material displays unique adsorption behavior and extremely high specificity for binding CO2. We compare measurements at the N and O K-edges with first-principles calculations and discuss how these results compare to proposed adsorption mechanisms for this MOF.

Probing CO<sub>2</sub> adsorption in metal-organic frameworks using X-ray spectroscopy

247th National Meeting (2014)

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Probing CO2 adsorption in metal-organic frameworks using X-ray spectroscopy

Probing CO₂ adsorption in metal-organic frameworks using X-ray spectroscopy