Reversible CO Binding Enables Tunable CO/H2 and CO/N2 Separations in Metal鈥揙rganic Frameworks with Exposed Divalent Metal Cations

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• 作者：Eric D. Bloch ; Matthew R. Hudson ; Jarad A. Mason ; Sachin Chavan ; Valentina Crocell脿 ; Joshua D. Howe ; Kyuho Lee ; Allison L. Dzubak ; Wendy L. Queen ; Joseph M. Zadrozny ; Stephen J. Geier ; Li-Chiang Lin ; Laura Gagliardi ; Berend Smit ; Jeffrey B. Neaton ; Silvia Bordiga ; Craig M. Brown ; Jeffrey R. Long
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：July 30, 2014
• 年：2014
• 卷：136
• 期：30
• 页码：10752-10761
• 全文大小：482K
• ISSN：1520-5126

文摘

Six metal鈥搊rganic frameworks of the M₂(dobdc) (M = Mg, Mn, Fe, Co, Ni, Zn; dobdc^{4鈥?/sup> = 2,5-dioxido-1,4-benzenedicarboxylate) structure type are demonstrated to bind carbon monoxide reversibly and at high capacity. Infrared spectra indicate that, upon coordination of CO to the divalent metal cations lining the pores within these frameworks, the C鈥揙 stretching frequency is blue-shifted, consistent with nonclassical metal-CO interactions. Structure determinations reveal M鈥揅O distances ranging from 2.09(2) 脜 for M = Ni to 2.49(1) 脜 for M = Zn and M鈥揅鈥揙 angles ranging from 161.2(7)掳 for M = Mg to 176.9(6)掳 for M = Fe. Electronic structure calculations employing density functional theory (DFT) resulted in good agreement with the trends apparent in the infrared spectra and crystal structures. These results represent the first crystallographically characterized magnesium and zinc carbonyl compounds and the first high-spin manganese(II), iron(II), cobalt(II), and nickel(II) carbonyl species. Adsorption isotherms indicate reversible adsorption, with capacities for the Fe, Co, and Ni frameworks approaching one CO per metal cation site at 1 bar, corresponding to loadings as high as 6.0 mmol/g and 157 cm3/cm3. The six frameworks display (negative) isosteric heats of CO adsorption ranging from 52.7 to 27.2 kJ/mol along the series Ni > Co > Fe > Mg > Mn > Zn, following the Irving鈥揥illiams stability order. The reversible CO binding suggests that these frameworks may be of utility for the separation of CO from various industrial gas mixtures, including CO/H₂ and CO/N₂. Selectivities determined from gas adsorption isotherm data using ideal adsorbed solution theory (IAST) over a range of gas compositions at 1 bar and 298 K indicate that all six M₂(dobdc) frameworks could potentially be used as solid adsorbents to replace current cryogenic distillation technologies, with the choice of M dictating adsorbent regeneration energy and the level of purity of the resulting gases.}