V Guillerm

Publications (2)6.37 Total impact

• Source

  Available from: Alexander G Stepanov

  Article: Probing the Dynamics of the Porous Zr Terephthalate UiO-66 Framework Using 2 H NMR and Neutron Scattering

  D I Kolokolov, ∥ A G Stepanov, V Guillerm, C Serre, B Frick, H Jobic
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  ABSTRACT: 2 H NMR and quasi-elastic neutron scattering techniques have been used to study the rotational dynamics of the 1,4-benzene-dicarboxylate (BDC) linkers in the porous cubic UiO-66(Zr) metal−organic framework (MOF). The rotation of the benzene rings in the BDC linkers is at the limit of detection of the neutron technique, but it fits perfectly on the 2 H NMR time scale. The aromatic rings in the UiO-66 framework exhibit the lowest rotational barrier compared to other MOFs, the activation energy for π-flips being 30 kJ mol −1 . However, instead of having well-defined flipping rates like in MOF-5, MIL-47, or MIL-53, UiO-66(Zr) shows a distribution of flipping correlation times, probably due to local disorder in the structure. Because of the rotational motion of the benzene rings, the effective size of the microporous windows in UiO-66(Zr) appears to be temperature dependent. 1. INTRODUCTION The efficiency of a given microporous system, e.g., for separation processes, depends on the interaction mechanism between the adsorbed molecular species and the hosting material; i.e., it is a matter of interaction on the molecular scale. This interaction governs not only the thermodynamics of a given adsorption-based process but also its kinetics, the second fundamental parameter that can strongly affect the overall efficiency. Metal−organic frameworks (MOFs) or porous coordination polymers (PCPs) represent a rapidly expanding family of novel nanoporous materials with potential applications in the fields of adsorption or separation of gases and liquids, catalysis, drug delivery, and others. 1−4 MOFs belong to a class of coordination polymers built from metal oxide nodes connected together by bridging organic "linkers" (carboxylates, azolates, phospho-nates, etc.). The growing interest in these hybrid porous materials relies on their high surface area and accessible free pore volume as well as on their unique chemical versatility. 5 The latter is a remarkable feature, as the sorbent/sorbate interaction can be tuned by a proper choice of the metal center or of the organic linker, either through direct synthesis or postsynthesis modification, to meet the desired properties. 5,6 Some MOFs represent also a complex and intriguing type of regular porous system, as their framework is flexible and can expand or even "breathe" 7 upon adsorption, which additionally influences the guest molecules.
  The Journal of Physical Chemistry C 06/2012; 116(22):12131. · 4.80 Impact Factor
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  Available from: Alexander G Stepanov

  Article: Comparison of the dynamics of MIL-53(Cr) and MIL-47(V) frameworks using neutron scattering and DFT methods

  D.I. Kolokolov, H. Jobic, A.G. Stepanov, M. Plazanet, M. Zbiri, J. Ollivier, V. Guillerm, T. Devic, C. Serre, G. Férey
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  ABSTRACT: The low-frequency modes of MIL-47(V) and MIL-53(Cr) frameworks have been measured by inelastic neutron scattering. The librational modes of benzene are very close in frequency in the two structures. First-principles calculations have been performed to assign the measured spectra. The calculated values of the rotational barriers of the benzene rings are in reasonable agreement with experimental data. The relatively large barriers (413–588 meV) explain the absence of quasi-elastic broadening on the neutron time scale.
  The European Physical Journal Special Topics 04/2012; 189(1):263-271. · 1.56 Impact Factor