Institute of Physics, Chair of Solid State and Material Science, Augsburg University, Universitätsstrasse 1, 86135 Augsburg, Germany.
Chemistry. 2011 Feb 7;17(6):1837-48. doi: 10.1002/chem.201001872. Epub 2011 Jan 12.
A highly porous member of isoreticular MFU-4-type frameworks, [Zn(5)Cl(4)(BTDD)(3)] (MFU-4l(arge)) (H(2)-BTDD=bis(1H-1,2,3-triazolo[4,5-b],[4',5'-i])dibenzo[1,4]dioxin), has been synthesized using ZnCl(2) and H(2)-BTDD in N,N-dimethylformamide as a solvent. MFU-4l represents the first example of MFU-4-type frameworks featuring large pore apertures of 9.1 Å. Here, MFU-4l serves as a reference compound to evaluate the origin of unique and specific gas-sorption properties of MFU-4, reported previously. The latter framework features narrow-sized pores of 2.5 Å that allow passage of sufficiently small molecules only (such as hydrogen or water), whereas molecules with larger kinetic diameters (e.g., argon or nitrogen) are excluded from uptake. The crystal structure of MFU-4l has been solved ab initio by direct methods from 3D electron-diffraction data acquired from a single nanosized crystal through automated electron diffraction tomography (ADT) in combination with electron-beam precession. Independently, it has been solved using powder X-ray diffraction. Thermogravimetric analysis (TGA) and variable-temperature X-ray powder diffraction (XRPD) experiments carried out on MFU-4l indicate that it is stable up to 500 °C (N(2) atmosphere) and up to 350 °C in air. The framework adsorbs 4 wt % hydrogen at 20 bar and 77 K, which is twice the amount compared to MFU-4. The isosteric heat of adsorption starts for low surface coverage at 5 kJ mol(-1) and decreases to 3.5 kJ mol(-1) at higher H(2) uptake. In contrast, MFU-4 possesses a nearly constant isosteric heat of adsorption of ca. 7 kJ mol(-1) over a wide range of surface coverage. Moreover, MFU-4 exhibits a H(2) desorption maximum at 71 K, which is the highest temperature ever measured for hydrogen physisorbed on metal-organic frameworks (MOFs).
一种具有高比表面积的同构微孔沸石 MFU-4 型骨架材料，[Zn(5)Cl(4)(BTDD)(3)]（MFU-4l(arge)）（H(2)-BTDD=双（1H-1,2,3-三唑[4,5-b],[4',5'-i]）二苯并[1,4]二恶英），是通过在 N,N-二甲基甲酰胺溶剂中使用 ZnCl(2) 和 H(2)-BTDD 合成的。MFU-4l 是具有 9.1 Å 大孔径的 MFU-4 型骨架材料的第一个实例。在这里，MFU-4l 被用作参考化合物，以评估以前报道的 MFU-4 独特和特定气体吸附特性的起源。后者的骨架具有 2.5 Å 的窄孔径，只允许足够小的分子通过（如氢气或水），而动力学直径较大的分子（如氩气或氮气）则被排除在外。MFU-4l 的晶体结构通过直接从单个纳米尺寸晶体的 3D 电子衍射数据中使用电子衍射层析（ADT）结合电子束进动原位解出。它也可以通过粉末 X 射线衍射独立解出。对 MFU-4l 进行的热重分析（TGA）和变温粉末 X 射线衍射（XRPD）实验表明，它在 500°C（N(2)气氛）下稳定，在空气中稳定至 350°C。该骨架在 20 巴和 77 K 下吸附 4 wt %的氢气，是 MFU-4 的两倍。吸附等温线的等吸附热在低表面覆盖率时从 5 kJ mol(-1)开始，在更高的氢气吸收时降至 3.5 kJ mol(-1)。相比之下，MFU-4 在很宽的表面覆盖率范围内表现出约 7 kJ mol(-1)的几乎恒定的等吸附热。此外，MFU-4 在 71 K 时表现出氢气解吸最大值，这是金属有机骨架（MOFs）上物理吸附氢气的最高温度。
