Department of Chemistry, University of California , Berkeley, California 94720, United States.
J Am Chem Soc. 2014 Jul 30;136(30):10752-61. doi: 10.1021/ja505318p. Epub 2014 Jul 18.
Six metal-organic frameworks of the M2(dobdc) (M = Mg, Mn, Fe, Co, Ni, Zn; dobdc(4-) = 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-O stretching frequency is blue-shifted, consistent with nonclassical metal-CO interactions. Structure determinations reveal M-CO distances ranging from 2.09(2) Å for M = Ni to 2.49(1) Å for M = Zn and M-C-O angles ranging from 161.2(7)° for M = Mg to 176.9(6)° 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 cm(3)/cm(3). 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-Williams 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.
六种 M2(dobdc)（M = Mg、Mn、Fe、Co、Ni、Zn；dodobc(4-) = 2,5-二氧代-1,4-苯二甲酸根）结构类型的金属有机骨架被证明能够可逆地高容量地结合一氧化碳。红外光谱表明，当 CO 配位到这些骨架孔内的二价金属阳离子时，C-O 伸缩频率发生蓝移，与非经典金属-CO 相互作用一致。结构测定表明，M-CO 距离范围从 M = Ni 的 2.09(2) Å 到 M = Zn 的 2.49(1) Å，M-C-O 角度范围从 M = Mg 的 161.2(7)°到 M = Fe 的 176.9(6)°。采用密度泛函理论（DFT）的电子结构计算结果与红外光谱和晶体结构中明显的趋势吻合较好。这些结果代表了第一个结晶学上表征的镁和锌羰基化合物，以及第一个高自旋锰(II)、铁(II)、钴(II)和镍(II)羰基物种。吸附等温线表明，可逆吸附，Fe、Co 和 Ni 骨架在 1 巴下接近每个金属阳离子位点一个 CO，对应于高达 6.0 mmol/g 和 157 cm(3)/cm(3)的负载。六个骨架显示出 CO 吸附的（负）等焓随系列 Ni > Co > Fe > Mg > Mn > Zn 而变化，遵循 Irving-Williams 稳定性顺序，从 52.7 到 27.2 kJ/mol。可逆的 CO 结合表明，这些骨架可能在从各种工业气体混合物（包括 CO/H2 和 CO/N2）中分离 CO 方面具有实用价值。在 1 巴和 298 K 下，使用理想吸附溶液理论（IAST）从气体吸附等温线数据确定的选择性表明，所有六个 M2(dobdc) 骨架都有可能作为固体吸附剂替代当前的低温蒸馏技术，M 的选择决定了吸附剂的再生能量和所得气体的纯度水平。
