Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080, United States.
J Am Chem Soc. 2011 Aug 17;133(32):12849-57. doi: 10.1021/ja2051149. Epub 2011 Jul 21.
The unusual uptake behavior and preferential adsorption of CO(2) over N(2) are investigated in a flexible metal-organic framework system, Zn(2)(bdc)(2)(bpee), where bpdc = 4,4'-biphenyl dicarboxylate and bpee = 1,2-bis(4-pyridyl)ethylene, using Raman and IR spectroscopy. The results indicate that the interaction of CO(2) with the framework induces a twisting of one of its ligands, which is possible because of the type of connectivity of the carboxylate end group of the ligand to the metal center and the specific interaction of CO(2) with the framework. The flexibility of the bpee pillars allows the structure to respond to the twisting, fostering the adsorption of more CO(2). DFT calculations support the qualitative picture derived from the experimental analysis. The adsorption sites at higher loading have been identified using a modified van der Waals-Density Functional Theory method, showing that the more energetically favorable positions for the CO(2) molecules are closer to the C═C bond of the bpee and the C-C bond of the bpdc ligands instead of the benzene and pyridine rings of these ligands. These findings are consistent with changes observed using Raman spectroscopy, which is useful for detecting both specific guest-host interactions and structural changes in the framework.
使用拉曼和红外光谱研究了柔性金属有机骨架体系 Zn(2)(bdc)(2)(bpee)（其中 bpdc = 4,4'-联苯二甲酸酯，bpee = 1,2-双(4-吡啶基)乙烯）中 CO(2)的异常吸收行为和对 N(2)的优先吸附。结果表明，CO(2)与骨架的相互作用导致其配体之一发生扭曲，这是由于配体羧基端与金属中心的连接类型和 CO(2)与骨架的特定相互作用所致。bpee 支柱的灵活性允许结构对扭曲做出响应，从而促进更多 CO(2)的吸附。DFT 计算支持从实验分析得出的定性图像。使用改进的范德华-密度泛函理论方法确定了在较高负载下的吸附位置，表明 CO(2)分子更有利的位置更靠近 bpee 的 C═C 键和 bpdc 配体的 C-C 键，而不是这些配体的苯环和吡啶环。这些发现与拉曼光谱观察到的变化一致，拉曼光谱可用于检测客体-主体相互作用和骨架结构变化。
