Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kingdom and ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom and Diamond Light Source, Harwell Campus, Didcot, Oxford OX11 0DE, United Kingdom.
Department of Chemistry, NIS and INSTM Reference Centre, University of Turin, via Pietro Giuria 7, 10125 Torino, Italy.
Phys Rev Lett. 2014 Nov 21;113(21):215502. doi: 10.1103/PhysRevLett.113.215502. Epub 2014 Nov 20.
We present an unambiguous identification of low-frequency terahertz vibrations in the archetypal imidazole-based metal-organic framework (MOF) materials: ZIF-4, ZIF-7, and ZIF-8, all of which adopt a zeolite-like nanoporous structure. Using inelastic neutron scattering and synchrotron radiation far-infrared absorption spectroscopy, in conjunction with density functional theory (DFT), we have pinpointed all major sources of vibrational modes. Ab initio DFT calculations revealed the complex nature of the collective THz modes, which enable us to establish detailed correlations with experiments. We discover that low-energy conformational dynamics offers multiple pathways to elucidate novel physical phenomena observed in MOFs. New evidence demonstrates that THz modes are intrinsically linked, not only to anomalous elasticity underpinning gate-opening and pore-breathing mechanisms, but also to shear-induced phase transitions and the onset of structural instability.
我们对典型的咪唑基金属有机骨架（MOF）材料：ZIF-4、ZIF-7 和 ZIF-8 中的低频太赫兹振动进行了明确的识别，这些材料都采用沸石状纳米多孔结构。我们使用非弹性中子散射和同步辐射远红外吸收光谱，结合密度泛函理论（DFT），确定了所有主要的振动模式来源。从头算 DFT 计算揭示了太赫兹模式的复杂性质，使我们能够与实验建立详细的关联。我们发现，低能构象动力学提供了多种途径来阐明在 MOF 中观察到的新物理现象。新的证据表明，太赫兹模式不仅与为门控和孔呼吸机制提供基础的异常弹性有关，而且与剪切诱导的相变和结构失稳有关。
