TY - JOUR

T1 - Ultraslow Dynamics of a Framework Linker in MIL-53 (Al) as a Sensor for Different Isomers of Xylene

AU - Khudozhitkov, Alexander E.

AU - Jobic, Hervé

AU - Freude, Dieter

AU - Haase, Juergen

AU - Kolokolov, Daniil I.

AU - Stepanov, Alexander G.

PY - 2016/9/29

Y1 - 2016/9/29

N2 - MIL-53 (Al) is an important example of metal-organic frameworks (MOFs) with a flexible framework capable to efficiently separate ortho and para isomers of xylene at moderate temperatures. The MIL-53 MOF contains mobile terephthalate phenylene fragments that can be used as a dynamic probe to investigate the guest-host interactions and the origin of the separation selectivity. Here 2H NMR spin alignment echo technique for the first time was applied to probe ultraslow structural mobility (0.1-1 kHz) in MOFs materials, with particular application to MIL-53(Al) saturated with ortho or para isomers of xylene. A specific influence of different isomers of xylene adsorbed in the MOF pores on the rotation of the phenylenes in MIL-53 for the temperature range with proved separation selectivity (T < 393 K) is shown. It has been established that the rotation of phenylene fragments is sensitive to the type of xylene isomer. The phenylenes' rotation performs 1 order of magnitude slower in the presence of o-xylene (kortho = 70 s-1) compared to the same rotation in the presence of the other isomer, p-xylene (kpara = 800 s-1) at T ∼ 373 K. This is rationalized by a stronger interaction of the ortho isomer with the linker than the para isomer. This finding offers an understanding of the molecular mechanism of p- and o-xylene separation by MIL-53: stronger interaction of o-xylene with organic linker compared to p-xylene provides separation of these isomers on MIL-53.

AB - MIL-53 (Al) is an important example of metal-organic frameworks (MOFs) with a flexible framework capable to efficiently separate ortho and para isomers of xylene at moderate temperatures. The MIL-53 MOF contains mobile terephthalate phenylene fragments that can be used as a dynamic probe to investigate the guest-host interactions and the origin of the separation selectivity. Here 2H NMR spin alignment echo technique for the first time was applied to probe ultraslow structural mobility (0.1-1 kHz) in MOFs materials, with particular application to MIL-53(Al) saturated with ortho or para isomers of xylene. A specific influence of different isomers of xylene adsorbed in the MOF pores on the rotation of the phenylenes in MIL-53 for the temperature range with proved separation selectivity (T < 393 K) is shown. It has been established that the rotation of phenylene fragments is sensitive to the type of xylene isomer. The phenylenes' rotation performs 1 order of magnitude slower in the presence of o-xylene (kortho = 70 s-1) compared to the same rotation in the presence of the other isomer, p-xylene (kpara = 800 s-1) at T ∼ 373 K. This is rationalized by a stronger interaction of the ortho isomer with the linker than the para isomer. This finding offers an understanding of the molecular mechanism of p- and o-xylene separation by MIL-53: stronger interaction of o-xylene with organic linker compared to p-xylene provides separation of these isomers on MIL-53.

UR - http://www.scopus.com/inward/record.url?scp=84989808827&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.6b08114

DO - 10.1021/acs.jpcc.6b08114

M3 - Article

AN - SCOPUS:84989808827

VL - 120

SP - 21704

EP - 21709

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 38

ER -