Dresden 2011 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 22: Poster: Glass Transition and Dynamics of Liquids
CPP 22.4: Poster
Dienstag, 15. März 2011, 18:00–20:00, P2
Molecular relaxation processes in a MOF-5 structure revealed by broadband dielectric spectroscopy: signature of phenylene ring fluctuations — Stefan Frunza1, •Andreas Schönhals2, Ligia Frunza1, Paul Ganea1, Hendrik Kosslick3, Jörg Harloff4, and Axel Schulz3 — 1National Institute of Materials Physics, R-077125 Magurele, Romania — 2BAM Federal Institute for Materials Research and Testing, D-12205 Berlin, Germany — 3Leibnitz Institute for Catalysis at the University of Rostock, D-18059 Rostock, Germany — 4University of Rostock, Institute of Chemistry, D-18059 Rostock, Germany
The molecular mobility of a MOF-5 metal-organic framework was investigated by broadband dielectric spectroscopy. Three relaxation processes were revealed. The temperature dependence of their relaxation rates follows an Arrhenius law. The process observed at lower temperatures is attributed to bending fluctuations of the edges of the cages involving the Zn-O clusters. The processes (*region II*) at higher temperatures were assigned to fluctuations of phenyl rings in agreement with the NMR data found by Gould et al. [J. Am. Chem. Soc. 2008, 130, 3246]. The carboxylate groups might be also involved. The rotational fluctuations of the phenyl rings leading to the low frequency part of relaxation region II might be hindered either by some solvent molecules entrapped in the cages or by an interpenetrated structure and have a broad distribution of activation energies. The high frequency part of region II corresponds nearly to a Debye-like process: This is explained by a well-defined structure of empty pores.