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On the Role of Enthalpic and Entropic Contributions on the Conformational Free Energy Landscape of MIL-101(Cr) Structural Building Units

preprint
revised on 13.07.2020 and posted on 13.07.2020 by Loukas Kollias, David Cantu, Vassiliki-Alexandra Glezakou, Roger Rousseau, Matteo Salvalaglio
The thermo-structural behavior of metal-organic framework (MOF) precursors is responsible for regulating the introduction of defects in MOF structures during synthesis. In this paper, factors affecting the flexibility of MIL-101(Cr) half-secondary building units (half-SBUs) are evaluated in solution using enhanced sampling methods. In particular, entropic and enthalpic contributions to the conformational free energy landscape of isolated MIL-101(Cr) half-SBUs are calculated in water, in the presence and absence of ionic species (Na+ and F-), and in N, N-dimethylformamide (DMF). This analysis leads to the observation that the interplay between enthalpy and entropy determines the most probable conformational state for half-SBUs. Furthermore, the role of enthalpy and entropy in the conformational rearrangement of an SBU is investigated in water, noting that entropic contributions are essential to stabilize configurations that depart from those coherent with the MIL-101(Cr) crystal structure. This analysis highlights the importance of explicitly considering entropic effects on the configurational ensembles of MOF building units and highlights the significant impact they have on the relative stability of crystal-like and non-crystal-like conformers.

History

Email Address of Submitting Author

m.salvalaglio@ucl.ac.uk

Institution

University College London

Country

United Kingdom

ORCID For Submitting Author

0000-0003-3371-2090

Declaration of Conflict of Interest

No conflict of interest.

Version Notes

Revision 3, June 2020

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