Thursday, November 20, 2014

Abstract-Identifying the Role of Terahertz Vibrations in Metal-Organic Frameworks: From Gate-Opening Phenomenon to Shear-Driven Structural Destabilization

  • 1Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kingdom
  • 2ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom
  • 3Diamond Light Source, Harwell Campus, Didcot, Oxford OX11 0DE, United Kingdom
  • 4Department of Chemistry, NIS and INSTM Reference Centre, University of Turin, via Pietro Giuria 7, 10125 Torino, Italy
  • 5Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, United Kingdom
  • 6Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
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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 initioDFT 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.
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  • Published 20 November 2014
  • Received 1 August 2014
© 2014 American Physical Society

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