Abstract-Dielectric Properties of Metal-Organic Frameworks Probed via Synchrotron Infrared Reflectivity

Matthew R. Ryder, Zhixin Zeng, Yueting Sun, Irina Flyagina, Kirill Titov, E.M. Mahdi, Thomas D. Bennett, Bartolomeo Civalleri, Chris S. Kelley, Mark D. Frogley, Gianfelice Cinque, Jin-Chong Tan

https://arxiv.org/abs/1802.06702

We present the frequency-dependant (dynamic) dielectric response of a group of topical polycrystalline zeolitic imidazolate-based metal-organic framework (MOF) materials in the extended infrared spectral region. Using synchrotron-based FTIR spectroscopy in specular reflectance, in conjunction with density functional theory (DFT) calculations, we have revealed detailed structure-property trends linking the THz region dielectric response to framework porosity and structural density. The work demonstrates that MOFs are promising candidate materials not only for low-\k{appa} electronics applications but could also be pioneering for terahertz (THz) applications, such as next-generation broadband communications technologies.

Abstract-Detecting Molecular Rotational Dynamics Complementing the Low-Frequency Terahertz Vibrations in a Zirconium-Based Metal-Organic Framework

Matthew R. Ryder, Ben Van de Voorde, Bartolomeo Civalleri, Thomas D. Bennett, Sanghamitra Mukhopadhyay, Gianfelice Cinque, Felix Fernandez-Alonso, Dirk De Vos, Svemir Rudić, Jin-Chong Tan

(Submitted on 20 Mar 2017)

https://arxiv.org/abs/1703.06827

We show clear experimental evidence of co-operative terahertz (THz) dynamics observed below 3 THz (~100 cm-1), for a low-symmetry Zr-based metal-organic framework (MOF) structure, termed MIL-140A [ZrO(O2C-C6H4-CO2)]. Utilizing a combination of high-resolution inelastic neutron scattering and synchrotron radiation far-infrared spectroscopy, we measured low-energy vibrations originating from the hindered rotations of organic linkers, whose energy barriers and detailed dynamics have been elucidated via ab initio density functional theory (DFT) calculations. For completeness, we obtained Raman spectra and characterized the alterations to the complex pore architecture caused by the THz rotations. We discovered an array of soft modes with trampoline-like motions, which could potentially be the source of anomalous mechanical phenomena, such as negative linear compressibility and negative thermal expansion. Our results also demonstrate coordinated shear dynamics (~2.5 THz), a mechanism which we have shown to destabilize MOF crystals, in the exact crystallographic direction of the minimum shear modulus (Gmin).

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

Matthew R. Ryder1,2,3, Bartolomeo Civalleri4, Thomas D. Bennett5, Sebastian Henke5, Svemir Rudić2, Gianfelice Cinque3, Felix Fernandez-Alonso2,6, and Jin-Chong Tan1,*

• 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

• *jin-chong.tan@eng.ox.ac.uk
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https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.215502

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.

DOI: http://dx.doi.org/10.1103/PhysRevLett.113.215502

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• Published 20 November 2014
• Received 1 August 2014

© 2014 American Physical Society

Abstract-Identifying the role of terahertz vibrations in metalorganic frameworks: From gate-opening phenomenon to shear-driven structural destabilization

Matthew R. Ryder, Bartolomeo Civalleri, Thomas D. Bennett, Sebastian Henke, Svemir Rudić, Gianfelice Cinque, Felix Fernandez-Alonso, and Jin-Chong Tan

http://journals.aps.org/prl/accepted/99077Yb0If312d3dd7a20130212ad398366d46c9c

We present an unambiguous identification of low-frequency terahertz (THz) 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.