Hoffman Alexander E J, Vanduyfhuys Louis, Nevjestić Irena, Wieme Jelle, Rogge Sven M J, Depauw Hannes, Van Der Voort Pascal, Vrielinck Henk, Van Speybroeck Veronique
Center for Molecular Modeling, Ghent University, Technologiepark 903, 9052 Zwijnaarde, Belgium.
Department of Solid State Sciences, Ghent University, Krijgslaan 281-S1, 9000 Ghent, Belgium.
J Phys Chem C Nanomater Interfaces. 2018 Feb 8;122(5):2734-2746. doi: 10.1021/acs.jpcc.7b11031. Epub 2018 Jan 8.
In this work, mid-infrared (mid-IR), far-IR, and Raman spectra are presented for the distinct (meta)stable phases of the flexible metal-organic framework MIL-53(Al). Static density functional theory (DFT) simulations are performed, allowing for the identification of all IR-active modes, which is unprecedented in the low-frequency region. A unique vibrational fingerprint is revealed, resulting from aluminum-oxide backbone stretching modes, which can be used to clearly distinguish the IR spectra of the closed- and large-pore phases. Furthermore, molecular dynamics simulations based on a DFT description of the potential energy surface enable determination of the theoretical Raman spectrum of the closed- and large-pore phases for the first time. An excellent correspondence between theory and experiment is observed. Both the low-frequency IR and Raman spectra show major differences in vibrational modes between the closed- and large-pore phases, indicating changes in lattice dynamics between the two structures. In addition, several collective modes related to the breathing mechanism in MIL-53(Al) are identified. In particular, we rationalize the importance of the trampoline-like motion of the linker for the phase transition.
在这项工作中，我们展示了柔性金属有机框架MIL-53(Al)不同（亚）稳定相的中红外（mid-IR）、远红外和拉曼光谱。进行了静态密度泛函理论（DFT）模拟，从而能够识别所有红外活性模式，这在低频区域是前所未有的。揭示了一种独特的振动指纹，它源于氧化铝骨架的拉伸模式，可用于清晰区分闭孔相和大孔相的红外光谱。此外，基于势能面的DFT描述进行的分子动力学模拟首次确定了闭孔相和大孔相的理论拉曼光谱。观察到理论与实验之间有极好的对应关系。低频红外光谱和拉曼光谱都显示出闭孔相和大孔相在振动模式上的主要差异，表明这两种结构之间晶格动力学的变化。此外，还识别出了与MIL-53(Al)中呼吸机制相关的几种集体模式。特别是，我们阐明了连接体类似蹦床的运动对相变的重要性。
