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

• Published in: Journal of physical chemistry. C 2015-04, Vol.119 (15), p.8217-8225
• Main Authors: Kolokolov, D. I, Jobic, H, Rives, S, Yot, P. G, Ollivier, J, Trens, P, Stepanov, A. G, Maurin, G
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.5b01465

A combination of experimental (quasi-elastic neutron scattering and 2H NMR) and computational (molecular dynamics) tools was used to uncover the molecular mobility of benzene trapped inside the flexible channel-type MIL-53 (Cr3+) MOF. This material was shown to undergo a contraction of the structure upon benzene adsorption with the formation of a narrow pore phase with a smaller aperture. This confinement was found to strongly influence the dynamics of the guest: benzene diffuses in a region centered in the middle of the pore by a 1D-jump translational mechanism along the tunnel ruled by the presence of the μ2-OH groups present at the MOF pore wall. This translational diffusion is combined with a fast uniaxial rotational motion around the C 6-axis. Any other rotational motion that involves the tumbling of the phenyl rings about the channel axis is much less probable due to a high activation energy barrier (49 kJ mol–1). In this way benzene can be pictured as a rotating disc that diffuses rapidly through the central part of the channel by short jumps between neighboring low energy basins located in the vicinity of the μ2-OH groups of the MIL-53 channels.