TY - JOUR

T1 - Probing the Guest-Mediated Structural Mobility in the UiO-66(Zr) Framework by 2H NMR Spectroscopy

AU - Khudozhitkov, Alexander E.

AU - Jobic, Hervé

AU - Kolokolov, Daniil I.

AU - Freude, Dieter

AU - Haase, Jürgen

AU - Stepanov, Alexander G.

PY - 2017/6/1

Y1 - 2017/6/1

N2 - The solid-state 2H NMR technique (analysis of both the spectrum line shape and the spin-lattice relaxation) was used to probe both slow and fast dynamical modes of the phenylene fragments of terephthalate linkers of the UiO-66(Zr) framework affected by the presence of benzene guest in the pores of the material. Such approach allowed us to probe different motions within a broad range of time scale, 10-3-10-11 s. The internal dynamics in the UiO-66(Zr) framework is represented by torsional motions of the phenylene fragment of the linker including 2-site 180° flips (π-flips) of the plane of the phenylene ring and its restricted librations. In the presence of benzene loaded in the MOF pores the rate of π-flips decreases essentially and the activation barrier for this motion increases. The activation barrier has been found to increase almost in a linear fashion on benzene loading. Such observation is surprisingly unique among other MOFs with mobile linkers, like MIL-53(Al) or MOF-5. The fast librational motion occurs on a scale of ∼1010 Hz and shows no notable dependence on the guest loading. It has been established that anisotropy of T1 relaxation of the 2H NMR powder pattern of the phenylene fragments is especially sensitive to the librational motion when this motion is in a range of 107-1011 Hz. Within this range of libration frequencies, analysis of the anisotropic spin-lattice (T1) relaxation allows quantitative estimation of the rate of librational motion.

AB - The solid-state 2H NMR technique (analysis of both the spectrum line shape and the spin-lattice relaxation) was used to probe both slow and fast dynamical modes of the phenylene fragments of terephthalate linkers of the UiO-66(Zr) framework affected by the presence of benzene guest in the pores of the material. Such approach allowed us to probe different motions within a broad range of time scale, 10-3-10-11 s. The internal dynamics in the UiO-66(Zr) framework is represented by torsional motions of the phenylene fragment of the linker including 2-site 180° flips (π-flips) of the plane of the phenylene ring and its restricted librations. In the presence of benzene loaded in the MOF pores the rate of π-flips decreases essentially and the activation barrier for this motion increases. The activation barrier has been found to increase almost in a linear fashion on benzene loading. Such observation is surprisingly unique among other MOFs with mobile linkers, like MIL-53(Al) or MOF-5. The fast librational motion occurs on a scale of ∼1010 Hz and shows no notable dependence on the guest loading. It has been established that anisotropy of T1 relaxation of the 2H NMR powder pattern of the phenylene fragments is especially sensitive to the librational motion when this motion is in a range of 107-1011 Hz. Within this range of libration frequencies, analysis of the anisotropic spin-lattice (T1) relaxation allows quantitative estimation of the rate of librational motion.

KW - METAL-ORGANIC FRAMEWORK

KW - TEREPHTHALATE PHENYLENES

KW - COORDINATION POLYMERS

KW - ROTATIONAL-DYNAMICS

KW - NEUTRON-SCATTERING

KW - MOLECULAR ROTORS

KW - DIFFUSION

KW - RELAXATION

KW - ZIF-8

KW - MOFS

UR - http://www.scopus.com/inward/record.url?scp=85020689692&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.7b03259

DO - 10.1021/acs.jpcc.7b03259

M3 - Article

AN - SCOPUS:85020689692

VL - 121

SP - 11593

EP - 11600

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 21

ER -