Experimental and Simulation Evidence of a Corkscrew Motion for Benzene in the Metal–Organic Framework MIL-47

Abstract

Some bacteria move with a corkscrew motion, meeting less resistance from surrounding water. A spiral movement is also considered during RNA polymerase translocation and it has been observed for water and proteins. We have found that benzene molecules confined in the metal−organic framework MIL-47 move in a corkscrew fashion. This spectacular diffusion effect could be put into evidence by combining experimental and computation tools; the two experimental techniques, quasielastic neutron scattering and 2 H NMR, cover a wide range of time scales.

Diffusion of Benzene in the Breathing Metal–Organic Framework MIL-53(Cr): A Joint Experimental–Computational Investigation

“…These Ds are slightly lower than the experimental values we previously reported in MIL-47(V 4+ ) (from 1.2 to 2.2 × 10 −9 m 2 /s in the temperature range 300−370 K). 13 In order to probe more precisely the rotational mobility of benzene inside the MIL-53(Cr 3+ ) channels, we followed the 2 H NMR spectra line shape evolution of the deuterated compound over a broad temperature region. The results are presented in Figure 8.…”

“…The observed Q eff value is characteristic of a fast uniaxial rotation of benzene about the C 6 symmetry axis. 13,57,58 13 and MOF-5. 66 In almost all reported cases, the C 6 rotation of benzene is characterized by the lowest activation barrier and it represents the fastest intramolecular dynamical mode.…”

“…13 However, due to the high activation barrier its resulting rate is rather low, i.e. at moderate temperatures (T < 400 K) these out-of-plane reorientations are strongly hindered.…”

“…4−7 In contrast, only two studies were devoted to gain insight into the kinetics of the benzene and the xylenes molecules confined into the pores of MIL-47(V 4+ ) with the evidence of an unusual diffusion mechanism corresponding to corkscrew motions along the channel. 13,14 The dynamics of these aromatics is expected to be more complex in the MIL-53 series as these solids (i) contain hydroxyl functions present at the M 3+ -O-M 3+ links (μ 2 -OH groups) which might act as strong attractive sites for the aromatics and/or as a steric barrier that hinders their mobility and (ii) undergo a structural contraction (also called as structural flexibility, or "breathing") upon adsorption which leads to a narrower section available for the molecules to reorientate. 3,15 As far as we know, neither experimental nor simulated data are reported yet on the dynamics of aromatics in such a breathing MOF.…”

Metal‐Organic Frameworks: Harmful Gas Removal

“…They demonstrated that benzene molecules interact strongly with the inorganic vertex of the MOF-5 framework with heats of adsorption at about 42 kJ mol −1 , as compared to light molecules, such as H 2 or CH 4 . Kolokolov et al 83 investigated the dynamics of benzene entrapped in the MIL-47(V) by quasielastic neutron scattering (QENS) and solid-state 2 H NMR, combined with molecular simulations. They obtained excellent agreement between QENS and molecular simulations on the quantitative study of molecular motion of fluids adsorbed in MIL-47(V).…”