Remarkable gas adsorption properties of zeolitic imidazolate frameworks (ZIFs) are believed to be tightly related to a flexible nature of organic linkers in these compounds. We present a low-frequency dielectric spectroscopy study of dynamic effects in a ZIF-90 hybrid compound. Experiments of dehydrated framework reveal slow motion of the imidazolate-2-carboxyaldehyde linker in the kilohertz frequency range. Measurements of hydrated compound indicate two additional dynamic processes related to the adsorbed water molecules. These processes are assigned to the proton conductivity and relaxation of the supercooled water confined within the pores of the framework. We also study linker dynamics of dehydrated ZIF-90 in vacuum and under different gas atmospheres, revealing that the linker motion is significantly hindered by the guest molecules.

We present a dielectric spectroscopy study of dipolar dynamics in the hydrated UiO-66(Zr) type metal-organic frameworks (MOFs) functionalized with −NH 2 and −F groups. Experiments are performed in a broad temperature and frequency ranges allowing us to probe several dipolar relaxations. For both samples at temperature below 220 K, we observe confined supercooled water dynamics, which can be described by the Arrhenius law. At slightly higher temperature, a second less pronounced dipolar relaxation is identified, and its origin is discussed. At even higher temperature, the dielectric permittivity exhibits anomalous increase with increasing temperature due to the proton conductivity. Upon further heating, the permittivity shows a sudden decrease indicating a reversible removal of water molecules. Measurements of the dehydrated samples reveal absence of all three dipolar processes.