Metastable sorption state of a metal-organic porous material determined by in situ synchrotron powder diffraction
Metastable sorption state of a metal-organic porous material determined by in situ synchrotron powder diffraction
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DOI：
10.1002/anie.200600976
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发表时间：
2006-01-01
影响因子：
16.6
通讯作者：
Kobayashi, Tatsuo C.
中科院分区：
文献类型：
--
作者：
Kubota, Yoshiki;Takata, Masaki;Kobayashi, Tatsuo C.
4932 2006 Wiley-VCH Verlag GmbH & Co. KGaA，魏因海姆安吉。化学。国际。埃德。 2006, 45, 4932–4936 金属有机物的特征。[5]动态孔隙可能来自一种具有多稳定性的“软”框架，其状态在两个对应部分之间来回变化；或者对于相同的外场参数值，系统可以存在于一种或两种状态。主体框架响应客体分子的结构重排从“开放”相进入“封闭”相。 MOMM 也可能是一类独特的材料，其特性不同于刚性多孔材料。虽然到目前为止，具有饱和客体量的 MOMM 的吸附曲线已经得到了很好的表征，[6] 但它们的中间曲线仍然未知。确定客体分子如何被识别并最终被纳米孔限制非常重要。对中间态的深入了解为我们提供了一种可行的多孔框架设计，将其结构改变为非常适合所需客体分子的结构，并形成有效的调节系统。因此，在整个吸附现象中，不仅需要主体框架的基本结构信息，还需要客体分子的基本结构信息。 X射线衍射是最强大的方法之一，可以直接提供吸附分子的结构信息。在此，我们通过原位同步加速器粉末衍射技术报道了 MOMM 纳米通道中气体吸附过程中中间相的结构分析。之前，[2]我们报道了乙炔气体在 CPL-1（具有柱层结构的配位聚合物 1：Cu2 (pzdc) 2 (pyz)，其中 pzdc 是吡嗪-2, 3-二羧酸酯，pyz 是吡嗪）上的吸附。[7]通过精确的结构分析，发现乙炔分子通过与不配位的羧酸氧原子形成双氢键而被捕获。无水空心相（I相）和饱和吸附相（S相）之间气体吸附的原位粉末衍射图显示了与S相混合的另一相。在解吸过程中也观察到了这一点。 CPL-1 的乙炔气体吸附等温线在 270 K 处显示出在极低压区域急剧上升并达到饱和。在上升过程中，每单位孔大约有 0.7 个分子，有一个明显的台阶。这些数据表明存在吸附中间相，我们称之为中间相M。在先前报道的 10 kPa 乙炔气压的衍射图中，[2] S 相和 M 相是混合的。通过仔细调节温度和气压，我们成功地获得了单相 M 相。图 1 显示了在 150 kPa 恒定气压下 CPL-1 与乙炔的衍射图的温度依赖性。样品从 390 K 开始冷却。360 K 时衍射图样的变化表明乙炔吸附已经开始。随后，另一个相（指定为 PhaseS）出现在 360K 以下。 M相的峰值强度逐渐降低，S相的峰值强度逐渐增加。分析了单相M 在360K 下的衍射图样。
4932 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2006, 45, 4932–4936 characteristic of metal–organic species.[5] Dynamic pores could come from a sort of “soft” framework with multistability, whose states go back and forth between two counterparts; or a system could exist in one or two states for the same values of external field parameters. The structural rearrangement of the host framework in response to guest molecules proceeds from the “open” phase to the “closed” phase. The MOMMs could also be a unique class of materials with characteristics unlike those of rigid porous materials. While sorption profiles of MOMMs with saturated amounts of guests have been well characterized so far,[6] their intermediate profiles are still unknown. It is important to determine how guest molecules are recognized and finally confined by nanopores. An in-depth understanding of the intermediate state provides us with a feasible design for a porous framework which changes its structure into one well suited to a desired guest molecules and results in an efficient accommodation system. Therefore, fundamental structural information on not only the host framework but also the guest molecules is required throughout adsorption phenomena. X-ray diffraction is one of the most powerful methods that can directly provide structural information on the adsorbed molecules. Herein we report the structure analysis of an intermediate phase in the process of gas adsorption in the nanochannels of an MOMM by in situ synchrotron powder diffraction.Previously,[2] we reported adsorption of acetylene gas on CPL-1 (coordination polymer 1 with pillared-layer structure: Cu2 (pzdc) 2 (pyz) where pzdc is pyrazine-2, 3-dicarboxylate and pyz is pyrazine).[7] From accurate structural analysis, acetylene molecules were found to be trapped by forming double hydrogen bonds with uncoordinated carboxylate oxygen atoms. In situ powder diffraction patterns for gas adsorption between the anhydrous hollow phase (phaseI) and the saturated adsorbed phase (phase S) revealed another phase mixed with phase S. It was also observed in the desorption process. The acetylene gas adsorption isotherm for CPL-1 at 270 K shows a steep rise in the very low pressure region and reaches saturation. During the rise, a step is evident at about 0.7 molecules per unit pore. These data suggest the existence of an intermediate phase of adsorption, which we call intermediate phaseM. In the diffraction patterns for an acetylene gas pressure of 10 kPa reported previously,[2] phases S and M are mixed. By careful adjustment of both temperature and gas pressure, we succeeded in obtaining phase M as a single phase. Figure 1 shows the temperature dependence of the diffraction patterns of CPL-1 with acetylene under a constant gas pressure of 150 kPa. The sample was cooled from 390 K. The change in diffraction pattern at 360 K indicates that acetylene adsorption has started. Subsequently, another phase, assigned as phaseS, appeared below 360K. The peak intensities of phase M gradually decreased and those of phase S increased. The diffraction pattern at 360K for single phaseM was analyzed.