Journal Article

PUBDB-2025-03776

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Molecular fluctuations in mixed-metal MOF-74: influence of the metal composition

Yildirim, A.DESY* ; Haug, T. C. V. ; Fröba, M. ; Huber, P. (Corresponding author)DESY* ; Schönhals, A.

2025
RSC Publishing London

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Please use a persistent id in citations: doi:10.1039/D5RA05357A  doi:10.3204/PUBDB-2025-03776

Abstract: A selected series of metal–organic frameworks M-MOF-74 (M = Mg, Co, Ni) and mixed metal MM-MOF-74 (Mg/Co or Mg/Ni) with different compositions of metal atoms have been prepared and further investigated by broadband dielectric spectroscopy (BDS) in a wide temperature range. The dielectric spectra show at least two relaxation processes. Process-A is observed only for the Ni-containing MOFs and is attributed to localized fluctuations of the metal oxide corners. Relaxation processes-B and -C are observed for all prepared MOFs, except that process-B is not observed for Ni-MOF-74. Large-angle fluctuations such as free rotations of the linkers can be excluded due to the structure of MOF-74, but small-angle fluctuations such as torsions are possible. According to numerical simulations carried out for MOF-74, process-B can be attributed to inward and outward fluctuations of the linkers relative to the pore center. Process-C is related to small-angle rotational fluctuations of the linker together with co-rotations of the metal nodes. The latter interpretation is supported by the dependence of the activation energy of the relaxation rate of process-C on the metal composition of the MOFs, which is discussed in terms of the bond lengths between the metal atoms and the linker which decrease in the sequence Mg, Co and Ni.

Note: This work was funded by the Deutsche For-schungsgemeinscha (DFG, German Research Foundation) –192346071 and supported in the frame of the LFF-project ’Control of the special properties of water in nanopores' (LFF-FV68-2019), enanced by the BWFGB. The authors thank DrFrank Hoffmann for valuable discussions.

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Contributing Institute(s):

1. CIMMS-RA Center for integr. Multiscale M (CIMMS)

Research Program(s):

1. 632 - Materials – Quantum, Complex and Functional Materials (POF4-632) (POF4-632)
2. SFB 986 C03 - Lithographisch gesteuerte Assemblierung und ALD-Beschichtung von 2D- und 3D-Porenstrukuren für die Thermophotovoltaik und als thermische Barriereschichten (C03) (221133061) (221133061)

Experiment(s):

1. No specific instrument

Appears in the scientific report 2025

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