TY - JOUR

T1 - Uncovering the Rotation and Translational Mobility of Benzene Confined in UiO-66 (Zr) Metal-Organic Framework by the 2H NMR-QENS Experimental Toolbox

AU - Kolokolov, Daniil I.

AU - Maryasov, Alexander G.

AU - Ollivier, Jacques

AU - Freude, Dieter

AU - Haase, Jürgen

AU - Stepanov, Alexander G.

AU - Jobic, Hervé

PY - 2017/2/9

Y1 - 2017/2/9

N2 - A combination of experimental quasi-elastic neutron scattering (QENS) and deuterium solid-state nuclear magnetic resonance (2H NMR) techniques was used to uncover the molecular mobility of benzene confined in UiO-66 (Zr) MOF with a 3D cage-window-cage type porous network topology. We have shown that tetrahedral and octahedral cages of UiO-66 offer notably different states of confinement for benzene. Below 163 K, the guest molecules of benzene are represented by two different dynamic states: in the smaller (tetrahedral) cage the benzene is able to exhibit only anisotropic C6 rotation and some limited librations. In the octahedral cage, there is enough space for additional C2 axial rotation and the isotropic random reorientation. Rotational motions have been characterized by the rate constants and corresponding activation energies. The two dynamic states merge as the temperature increases due to translational jump diffusion with the limiting step being the passage through the window between the cages. Both techniques show similar activation barrier for the diffusion of 25-27 kJ mol-1 and a diffusion coefficient D = 3.3 × 10-11 m2 s-1 at 400 K. The diffusion process is described by a migration via 1 nm long jumps among octa- and tetrahedral cages. The 2H NMR gives the correlation times for both the elementary step of diffusion (jump exchange between neighboring octa- and tetrahedral cages) and ≈58 time slower long-range isotropic migration process.

AB - A combination of experimental quasi-elastic neutron scattering (QENS) and deuterium solid-state nuclear magnetic resonance (2H NMR) techniques was used to uncover the molecular mobility of benzene confined in UiO-66 (Zr) MOF with a 3D cage-window-cage type porous network topology. We have shown that tetrahedral and octahedral cages of UiO-66 offer notably different states of confinement for benzene. Below 163 K, the guest molecules of benzene are represented by two different dynamic states: in the smaller (tetrahedral) cage the benzene is able to exhibit only anisotropic C6 rotation and some limited librations. In the octahedral cage, there is enough space for additional C2 axial rotation and the isotropic random reorientation. Rotational motions have been characterized by the rate constants and corresponding activation energies. The two dynamic states merge as the temperature increases due to translational jump diffusion with the limiting step being the passage through the window between the cages. Both techniques show similar activation barrier for the diffusion of 25-27 kJ mol-1 and a diffusion coefficient D = 3.3 × 10-11 m2 s-1 at 400 K. The diffusion process is described by a migration via 1 nm long jumps among octa- and tetrahedral cages. The 2H NMR gives the correlation times for both the elementary step of diffusion (jump exchange between neighboring octa- and tetrahedral cages) and ≈58 time slower long-range isotropic migration process.

KW - ELASTIC NEUTRON-SCATTERING

KW - NUCLEAR-MAGNETIC-RESONANCE

KW - SPIN-LATTICE RELAXATION

KW - DEUTERIUM NMR

KW - DYNAMICS

KW - DIFFUSION

KW - PROTON

KW - MOLECULES

KW - MOTION

KW - SIMULATION

UR - http://www.scopus.com/inward/record.url?scp=85026995505&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.6b12001

DO - 10.1021/acs.jpcc.6b12001

M3 - Article

AN - SCOPUS:85026995505

VL - 121

SP - 2844

EP - 2857

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 5

ER -