Reversible CO Scavenging via Adsorbate-Dependent Spin State Transitions in an Iron(II)–Triazolate Metal–Organic Framework

详细信息    查看全文

• 作者：Douglas A. Reed ; Dianne J. Xiao ; Miguel I. Gonzalez ; Lucy E. Darago ; Zoey R. Herm ; Fernande Grandjean ; Jeffrey R. Long
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：May 4, 2016
• 年：2016
• 卷：138
• 期：17
• 页码：5594-5602
• 全文大小：619K
• 年卷期：0
• ISSN：1520-5126

文摘

A new metal–organic framework, Fe-BTTri (Fe₃[(Fe₄Cl)₃(BTTri)₈]₂·18CH₃OH, H₃BTTri =1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene)), is found to be highly selective in the adsorption of CO over a variety of other gas molecules, making it extremely effective, for example, in the removal of trace CO from mixtures with H₂, N₂, and CH₄. This framework not only displays significant CO adsorption capacity at very low pressures (1.45 mmol/g at just 100 μbar), but, importantly, also exhibits readily reversible CO binding. Fe-BTTri utilizes a unique spin state change mechanism to bind CO in which the coordinatively unsaturated, high-spin Fe^II centers of the framework convert to octahedral, low-spin Fe^II centers upon CO coordination. Desorption of CO converts the Fe^II sites back to a high-spin ground state, enabling the facile regeneration and recyclability of the material. This spin state change is supported by characterization via infrared spectroscopy, single crystal X-ray analysis, Mössbauer spectroscopy, and magnetic susceptibility measurements. Importantly, the spin state change is selective for CO and is not observed in the presence of other gases, such as H₂, N₂, CO₂, CH₄, or other hydrocarbons, resulting in unprecedentedly high selectivities for CO adsorption for use in CO/H₂, CO/N₂, and CO/CH₄ separations and in preferential CO adsorption over typical strongly adsorbing gases like CO₂ and ethylene. While adsorbate-induced spin state transitions are well-known in molecular chemistry, particularly for CO, to our knowledge this is the first time such behavior has been observed in a porous material suitable for use in a gas separation process. Potentially, this effect can be extended to selective separations involving other π-acids.