Abstract
2H NMR spin–lattice relaxation was used to probe small-amplitude torsional vibrations (librations) of the organic terephthalate linkers in metal–organic framework (MOF) UiO-66(Zr) saturated with benzene molecules. In UiO-66 (Zr) the mobile phenylene fragments exhibit a complex rotational dynamics of the phenylene rings with fast librations and much slower π-flips around the C2 symmetry axis. We show that due to the intrinsic broad distribution of the π-flips rate, the relaxation process for the deuterium in the C–D group of phenylene fragment is multiexponential. Two main modes of T1 relaxation are clearly detected, corresponding to the fast T1fast and the slow T1slow relaxation. Based on the experimental observation of two-exponential relaxation, a computational model for this T1 relaxation behavior capable to reproduce the peculiarities of the MOF linkers dynamics was built. Computational analysis allows to establish that the librational motion affects mostly the T1slow, while T1fast remains unaffected ...
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