Unfolding the terahertz spectrum of soft porous crystals: rigid unit modes and their impact on phase transitions,Journal of Materials Chemistry A

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Unfolding the terahertz spectrum of soft porous crystals: rigid unit modes and their impact on phase transitions
Journal of Materials Chemistry A ( IF 10.7 ) Pub Date : 2022-08-08 , DOI: 10.1039/d2ta01678h
Alexander E. J. Hoffman ₁ , Irena Senkovska ₂ , Jelle Wieme ₁ , Alexander Krylov ₃ , Stefan Kaskel ₂ , Veronique Van Speybroeck ₁

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Phase transitions in flexible metal–organic frameworks or soft porous crystals are mediated by low-frequency phonons or rigid-unit modes. The alteration of specific building blocks may change the lattice dynamics of these frameworks, which can influence the phase transition mechanism. In this work, the impact of building block substitution on the rigid-unit modes in flexible MIL-53 analogs with a winerack topology will be investigated via ab initio lattice dynamics calculations. First, the accuracy of the theoretical simulations is verified via experimental Raman measurements, which provide unique fingerprint vibrations in the terahertz range to characterize the phase transition. Following analysis of the low-frequency vibrations shows that there exists a set of universal rigid-unit modes inducing translations and/or rotations of the building blocks. The theoretical results demonstrate that linker substitutions have a large effect on the rigid-unit mode frequencies, whereas this is less so for inorganic chain substitutions. These findings may help to rationally tune the phonon frequencies in soft porous crystals.

中文翻译：

展开软多孔晶体的太赫兹光谱：刚性单元模式及其对相变的影响

柔性金属-有机框架或软质多孔晶体中的相变由低频声子或刚性单元模式介导。特定构件的改变可能会改变这些框架的晶格动力学，从而影响相变机制。在这项工作中，将通过从头算晶格动力学计算研究构建块替换对具有酒架拓扑的柔性 MIL-53 类似物的刚性单元模式的影响。首先，通过验证理论模拟的准确性实验拉曼测量，提供太赫兹范围内的独特指纹振动来表征相变。对低频振动的分析表明，存在一组通用的刚性单元模式，可诱导构建块的平移和/或旋转。理论结果表明，接头取代对刚性单元模式频率有很大影响，而对于无机链取代则影响较小。这些发现可能有助于合理调整软多孔晶体中的声子频率。

更新日期：2022-08-11

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