Emergence of Cooperative Rotor Dynamics in Metal–organic Frameworks via Tuned Steric Interactions

22 September 2020, Version 1

Abstract

The organic components in metal-organic frameworks (MOFs) enjoy a unique situation: they are embedded in a crystalline lattice, yet, as they are separated from each other by tunable free space, a large variety of dynamic behavior can emerge. These rotational dynamics of the organic linkers are especially important due to their influence over properties such as gas adsorption and kinetics of guest release. In order to fully exploit linker rotation, it is necessary to engineer correlated linker dynamics to achieve their cooperative functional motion. Here, we show that for MIL-53, a topology with closely spaced rotors, the phenylene functionalization allows to tune the rotors’ steric environment, shifting linker rotation from completely static to rapid motions at frequencies above 100 MHz. For steric interactions that start to inhibit independent rotor motion, we identify for the first time the emergence of correlated rotation modes in linker dynamics. These findings pave the way for function-specific engineering of gearlike cooperative motion in MOFs.

Keywords

Metal-organic framework
linker dynamics
molecular rotors
Solid-state NMR
dielectric spectroscopy
Computational Chemistry
MOF

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