TY  - JOUR
AU  - Yildirim, Arda
AU  - Haug, Tabea C. V.
AU  - Fröba, Michael
AU  - Huber, Patrick
AU  - Schönhals, Andreas
TI  - Molecular fluctuations in mixed-metal MOF-74: influence of the metal composition
JO  - RSC Advances
VL  - 15
IS  - 35
SN  - 2046-2069
CY  - London
PB  - RSC Publishing
M1  - PUBDB-2025-03776
SP  - 29109 - 29118
PY  - 2025
N1  - 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.
AB  - 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.
LB  - PUB:(DE-HGF)16
DO  - DOI:10.1039/D5RA05357A
UR  - https://bib-pubdb1.desy.de/record/637143
ER  -