Probing Adsorption Interactions in Metal鈥揙rganic Frameworks using X-ray Spectroscopy

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• 作者：Walter S. Drisdell ; Roberta Poloni ; Thomas M. McDonald ; Jeffrey R. Long ; Berend Smit ; Jeffrey B. Neaton ; David Prendergast ; Jeffrey B. Kortright
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：December 4, 2013
• 年：2013
• 卷：135
• 期：48
• 页码：18183-18190
• 全文大小：442K
• 年卷期：v.135,no.48(December 4, 2013)
• ISSN：1520-5126

文摘

We explore the local electronic signatures of molecular adsorption at coordinatively unsaturated binding sites in the metal鈥搊rganic 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 which are suppressed upon adsorption of CO₂ and N,N鈥?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鈥揳dsorbate binding strength. The expanded MOF Mg₂(dobpdc) displays the same behavior upon adsorption of CO₂ and N,N鈥?dimethylethylenediamine. 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. Qualitative agreement between ambient-temperature experimental and 0 K theoretical spectra is good, with minor discrepancies thought to result from framework vibrational motion.