Dynamic motion of building blocks in porous coordination polymers
Dynamic motion of building blocks in porous coordination polymers
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DOI：
10.1002/anie.200603196
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发表时间：
2006-01-01
影响因子：
16.6
通讯作者：
Kitagawa, Susumu
中科院分区：
文献类型：
--
作者：
Horike, Satoshi;Matsuda, Ryotaro;Kitagawa, Susumu
7227 Angew. 2006，45，7226-7230 2006 Wiley-VCH Verlag GmbH & Co. KGaA，魏因海姆www. angewandte。有机层由1，4-二氮杂双环[2，2，2]辛烷分子柱撑（图3a）。5.7 5.7 2的矩形通道沿c方向沿着。在296 K时，二羧酸根离子的萘环在四个位置上是无序的（图3b）。尽管2中的萘环大于1中的吡嗪环，但2的骨架中有足够的空隙空间用于绕萘环的C1-C4轴旋转。我们通过使用[D 6] 1，4-萘二甲酸酯合成了部分氘代的2（2d），并通过XRD证实了骨架的拓扑结构与2的拓扑结构相同（参见支持信息）。无水2d在193-293 K下的2 HNMR光谱均由具有不同四极耦合常数的三个Pake双峰的叠加组成（参见支持信息），其来自萘环的三种类型的氘原子。在223 K以下，谱线随温度变化，我们对203-223 K的谱线进行了模拟。在这些模拟中，我们将萘环的运动模拟为围绕C1-C4轴的0，70，180和250 °角方向之间的四点翻转（基于2的无序结构）。从拟合确定的旋转速率范围从3.0 106 s1在203 K到5 107 s1在223 K。虽然2中的运动模式与1中的相同，但是由于填充和移动的基团的大小的差异，从Arrhenius图确定的2的53 kJ分子量1的活化能大约是1的6倍。苯在2上的吸附等温线是在298 K下测量的（参见辅助资料）。等温线显示I型曲线，表明微孔化合物的典型物理吸附过程。吸附的苯的最大量是每孔仅3个分子（100 mLgt 3 - 1）。考虑到苯分子的货车范德华体积（约. 89 3），[13]孔中苯分子所占体积为3 89= 267 3。然而，2的无序结构中的潜在溶剂区域的总体积为195 3每个孔，使用PLATON程序计算。[14]该值小于3个苯分子的体积，表明分子被密集地吸附在孔内。因此，苯分子可以干扰萘环围绕其C1-C4轴的自由旋转。在193-293 K下记录的苯吸附后2d（2d'C6 H6）的2 HNMR谱（参见支持信息）与无水2d的2 HNMR谱有很大不同。在整个温度范围内，观察到频率间隔为126 kHz的峰。小于103 sq-1的相关速率对应于缓慢交换或静态极限。因此，2d'C6 H6的旋转运动立即被客体吸附减速。苯分子脱附后，萘环在2d中的四位旋转重新开始。因此，通过客体吸附/脱附，旋转行为是可逆的（图4a）。2 'C6 H6的热重分析（TGA）显示，在25- 150 ℃下，每个孔损失近3个苯分子（观察值为24.1%，计算值为25.9%），相应的逐渐重量损失，没有任何明确的步骤（参见支持信息）。然而，在25- 1508 ℃的DSC曲线的加热循环中，观察到2 'C_6 H_6的急剧吸热转变，其焓为4.32 kJ·mol ~（-1），
7227 Angew. Chem. Int. Ed. 2006, 45, 7226–7230 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www. angewandte. org pillared by 1, 4-diazabicyclo [2, 2, 2] octane molecules (Figure 3a). Rectangular channels of 5.7 5.7 2 run along the c direction. At 296 K, the naphthalene ring of the dicarboxylate ion is disordered over four positions (Figure 3b). Even though the naphthalene ring in 2 is larger than the pyrazine ring in 1, there is enough void space in the framework of 2 for rotation about the C1–C4 axis of the naphthalene ring. We synthesized partially deuterated 2 (2d) by using [D6] 1, 4-naphthalenedicarboxylate and confirmed that the topology of the framework is identical to that of 2 by XRD (see Supporting Information). The 2HNMR spectra for anhydrous 2d at 193–293 K each consist of a superposition of three Pake doublets with different quadrupole coupling constants (see Supporting Information), which arise from the three types of deuterium atoms of the naphthalene ring. The spectra are temperature-dependent below 223K, and we carried out simulations for the spectra recorded at 203–223 K. In these simulations, we modeled the motion of the naphthalene rings as a four-site flip between orientations at angles of0, 70, 180, and 2508 about the C1–C4 axis (based on the disordered structure of 2). Rotation rates ranging from 3.0 106 sÀ1 at 203 K to 5 107 sÀ1 at 223 K were determined from the fitting. Although the mode of motion in 2 is the same as that in 1, the activation energy of 53 kJ molÀ1 of 2, determined from an Arrhenius plot, is approximately six times larger than that of 1, because of differences in packing and in the size of the mobile group.The sorption isotherm for benzene on 2 was measured at 298 K (see Supporting Information). The isotherm displays a Type I profile, indicative of a typical physisorption process for a microporous compound. The maximum amount of benzene adsorbed is only 3 molecules per pore (100 mLgÀ1). Considering the van der Waals volume of the benzene molecule (ca. 89 3),[13] the volume occupied by the benzene molecules in the pore is 3 89= 267 3. However, the total volume of the potential solvent area in the disordered structure of 2 is 195 3 per pore, as calculated using the PLATON program.[14] This value is smaller than the volume of 3 benzene molecules, suggesting that the molecules are densely adsorbed inside the pores. Thus, the benzene molecules could interfere with the free rotation of the naphthalene rings about their C1–C4 axes. The 2HNMR spectra of 2d after benzene adsorption (2d'C6H6) recorded at 193–293 K (see Supporting Information) are drastically different from those of anhydrous 2d. Over the whole temperature range, peaks with a frequency separation of 126 kHz are observed. The associated rate of less than 103 sÀ1 corresponds to the slow-exchange or static limit. Thus, the rotational motion of 2d'C6H6 is immediately decelerated by guest adsorption. After desorption of the benzene molecules, the four-site rotation of the naphthalene rings in 2d restarts. Therefore, the rotational behavior is reversible by guest adsorption/desorption (Figure 4a). Thermogravimetric analysis (TGA) of 2'C6H6 shows a gradual weight loss corresponding to the loss of nearly 3 benzene molecules per pore (observed 24.1%, calculated 25.9%) over 25–1508C, without any clear steps (see Supporting Information). However, in the heating cycle of the DSC curve of 2'C6H6 over 25–1508C, a sharp endothermic transition with an enthalpy of 4.32 kJmolÀ1 is observed at