Emergence of Coupled Rotor Dynamics in Metal–Organic Frameworks via Tuned Steric Interactions

Abstract

The organic components in metal−organic frameworks (MOFs) are unique: 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. To fully exploit linker rotation, such as in the form of molecular machines, 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 researchers 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 coupled rotation modes in linker dynamics. These findings pave the way for function-specific engineering of gear-like cooperative motion in MOFs.

Chiral Lanthanum Metal–Organic Framework with Gated CO2 Sorption and Concerted Framework Flexibility

“…The flexibility is also one reason why gas sorption measurements are more challenging to interpret for MOFs. 10 While different mechanisms for flexibility in MOFs have been identified, 3,11 and theoretically investigated, 12 they mostly rely on the behaviors of individual linkers, metal SBUs, their connection points, and sometimes external triggers (i.e., pressure, temperature, or interaction with guest molecules). Flexibility in MOFs and other porous framework materials such as zeolites can result in an observable "gate-opening" effect, where the accessible porosity of the materials with respect to certain guest molecule increases.…”

Molecular dissolution behaviors on porous membrane surface using hierarchical metal-organic framework lamellar membrane

“…Specifically, the content of N element on MOF-NH 2 nanosheet is tested to be 2.95%, matching well with the theoretical value calculated from lattice structure. This also implies that there is one -NH 2 group in a unit cell, [41] and the condition is identical for MOF-CH 3 nanosheet (Figures 1g and i), this implies the topological structure of MOF is explicitly constructed during synthetic process. Note that there is no extra group in the pore of MOF-BDC nanosheet, which is designed as a comparison.…”

“…It should be noted that the pore size of MOF-CH 3 and MOF-NH 2 nanosheets is smaller than that of MOF-BDC nanosheet, which is originated from the steric effect of -CH 3 and -NH 2 groups on the pores. [40,41] FTIR result (Figure S6) shows that, compared with MOF-BDC nanosheet, the typical C=O peak gives a blue shift for MOF-CH 3 and MOF-NH 2 nanosheets at 1360 ˜1380 cm -1 , owing to the presence of -CH 3 /-NH 2 groups adjacent to C=O group. Meanwhile, the grafting of -NH 2 groups bring a new strong peak at 1253 cm -1 , which assigned to Ar-N on FTIR and a typical characteristic peak of N element at 400 eV in XPS spectra of MOF-NH 2 (Figure S7).…”

A Crystalline Supramolecular Rotor Functioned by Dual Ultrasmall Polar Rotators†

“…[ 39 ] In such a model, the partial supramolecular self‐assembly between the building blocks greatly simplifies the covalent organic synthesis steps. Up to now, although some correlated rotators with a gearing motion mechanism have been reported, [ 40‐43 ] those simultaneously containing two discrete polar rotators that correspond to model (b)/(c) are hardly explored.…”