  UiO-66 (Zr) is a metal-organic framework known for its thermal and chemical
stability and wide range of possible applications. In particular, this material
has high separation selectivity of various hydrocarbon mixtures. Moreover, it
is was shown that the performance depends on the hydroxylation state of
material (reversible phase transition $Zr_{6}O_{4}(OH)_{4} {\longrightarrow}
Zr_{6}O_{6}$ at 250 - 300 ${\deg}C)$. Despite all the attention the UiO-66
received over past few years, the impact of the dehydroxylation on its
properties remains poorly understood. In this contribution we apply $^{2}$H NMR
experimental method in order to compare the mobility of butane isomers in
hydroxylated and dehydroxylated form of UiO-66. We provide estimations of the
translational diffusion coefficients and show which hydroxylation state of the
material has higher separation selectivity. Moreover, the impact of the
hydroxylation on the structural mobility of UiO-66 is discussed. Correlation
between parameters of structural dynamics and the diffusivity of guest
molecules indicates that for the microporous material with small windows even
subtle changes can lead to a tangible improvement of the properties.
