Ultraslow Dynamics of a Framework Linker in MIL-53 (Al) as a Sensor for Different Isomers of Xylene
Ultraslow Dynamics of a Framework Linker in MIL-53 (Al) as a Sensor for Different Isomers of Xylene
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DOI：
10.1021/acs.jpcc.6b08114
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发表时间：
2016-09-29
影响因子：
3.7
通讯作者：
Stepanov, Alexander G.
中科院分区：
文献类型：
--
作者：
Khudozhitkov, Alexander E.;Jobic, Herve;Stepanov, Alexander G.
MIL-53（Al）是具有柔性框架的金属有机框架（M0 F）的重要实例，其能够在中等温度下有效地分离二甲苯的邻位和帕拉异构体。MIL-53 MOF含有移动的对苯二甲酸亚苯基片段，其可用作动态探针以研究客体-主体相互作用和分离选择性的起源。本文首次将H-2NMR自旋排列回波技术应用于探测MOFs材料中的超低结构迁移率（0.1-1 kHz），特别适用于二甲苯邻位或帕拉异构体饱和的MIL-53（Al）。吸附在MOF孔中的二甲苯的不同异构体对MIL-53中的苯的旋转的特定影响被示出为具有证明的分离选择性的温度范围（T < 393 K）。已经确定，亚苯基片段的旋转对二甲苯异构体的类型敏感。在类似于373 K的T下，与在另一种异构体对二甲苯（k（对位）= 800 s（-1））存在下的相同旋转相比，在邻二甲苯（k（邻）= 70 s（-1））存在下，亚苯基的旋转慢1个数量级。这是合理的邻位异构体与接头的相互作用比帕拉异构体更强。这一发现提供了对MIL-53分离对二甲苯和邻二甲苯的分子机制的理解：与对二甲苯相比，邻二甲苯与有机连接体的更强相互作用提供了MIL-53上这些异构体的分离。
MIL-53 (Al) is an important example of metal-organic frameworks (MOFs) with a flexible framework capable to efficiently separate ortho and para isomers of xylene at moderate temperatures. The MIL-53 MOF contains mobile terephthalate phenylene fragments that can be used as a dynamic probe to investigate the guest-host interactions and the origin of the separation selectivity. Here H-2 NMR spin alignment echo technique for the first time was applied to probe ultraslow structural mobility (0.1-1 kHz) in MOFs materials, with particular application to MIL-53(Al) saturated with ortho or para isomers of xylene. A specific influence of different isomers of xylene adsorbed in the MOF pores on the rotation of the phenylenes in MIL-53 for the temperature range with proved separation selectivity (T < 393 K) is shown. It has been established that the rotation of phenylene fragments is sensitive to the type of xylene isomer. The phenylenes' rotation performs 1 order of magnitude slower in the presence of o-xylene (k(ortho) = 70 s(-1)) compared to the same rotation in the presence of the other isomer, p-xylene (k(para) = 800 s(-1)) at T similar to 373 K. This is rationalized by a stronger interaction of the ortho isomer with the linker than the para isomer. This finding offers an understanding of the molecular mechanism of p-and o-xylene separation by MIL-53: stronger interaction of o-xylene with organic linker compared to p-xylene provides separation of these isomers on MIL-53.