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Elucidating the vibrational fingerprint of the flexible metal-organic framework MIL-53(Al) using a combined experimental/computational approach

Authors
  • Hoffman, Alexander
  • Vanduyfhuys, Louis
  • Nevjestic, Irena
  • Wieme, Jelle
  • Rogge, Sven
  • Depauw, Hannes
  • Van Der Voort, Pascal
  • Vrielinck, Henk
  • Van Speybroeck, Veronique
Publication Date
Jan 01, 2018
Source
Ghent University Institutional Archive
Keywords
Language
English
License
Unknown
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Abstract

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.

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