Spatiotemporal Design of the Metal–Organic Framework DUT‐8(M)

Abstract

Switchable metal-organic frameworks change their structure in time and selectively open their pores adsorbing guest molecules, leading to highly selective separation, pressure amplification, sensing and actuation applications. The three-dimensional engineering of metal-organic frameworks has reached a high level of maturity, but spatiotemporal evolution opens a new perspective towards engineering materials in the 4 th dimension (time) by t-axis design, in essence exploiting the deliberate tuning of activation barriers. This work demonstrates the first example in which an explicit temporal engineering of a switchable metal-organic frameworkdeliberately tuned by variation of cobalt content. We present a spectrum of advanced analytical methods for analyzing the switching kinetics stimulated by vapor adsorption using in situ time resolved techniques ranging from ensemble adsorption and advanced synchrotron X-ray diffraction experiments to individual crystal analysis. A novel analysis technique based on microscopic observation of individual crystals in a microfluidic channel reveals the lowest limit for adsorption switching reported so far. The time constants for the bulk ensembles range from 2 -300 s. Differences in spatiotemporal response of crystal ensembles originate from a delay (induction) time that varies statistically and widens characteristically with increasing cobalt content reflecting increasing activation barriers.

Traffic Lights for Catalysis: Stimuli‐Responsive Molecular and Extended Catalytic Systems

“…In addition to organic or organometallic photoresponsive molecular compounds, much effort has been devoted to biomimetic systems or extended structures comprised of many photoswitchable molecules which are synergistically combined to affect catalytic outcomes. [61][62][63][64][65][66][113][114][115][116][117][118][119][120][121][122][123][124][125][126][127][128] There are several platforms, such as proteins, nanoparticles, and periodic structures which offer distinct opportunities for integration of photoswitches into different complex assemblies. [61][62][63][64][65][66][113][114][115][116][117][118][119][120][121][122][123][124][125][126][127][128] For example, photoresponsive molecules with azobenzene cores could be covalently embedded into a protein structure to affect its folding upon photoisomerization.…”

The role of phonons in switchable MOFs: a model material perspective

“…42,43 DUT-8 frameworks show remarkable selectivity in CO 2 /CH 4 , CH 2 Cl 2 /CHCl 3 /CH 3 Cl as well as D 2 /H 2 separation which can be tailored by metal substitution. 36,41,44,45 In seeking to establish a better understanding of the role of lattice vibrations impacted by the bonding strength of various metals (i.e. Ni, Co, Zn, and Cu), in the following, we combine complementary experimental techniques, in particular Raman spectroscopy, inelastic neutron scattering, and phonon acoustic spectroscopy, to unravel the impact of phonon frequencies on exibility.…”

Validating the Mechanism Underlying the Slacking of the Gate-Opening Behavior in Flexible Metal–Organic Frameworks Arising from the Application of External Force

“…Metal–organic frameworks (MOFs) are among the most promising materials for advancing the utilization of adsorbent-based separations. Because of their regular structures and high designability, − pore sizes and host–guest interactions, which determine the gas selectivity and amount adsorbed, can be controlled by customizing the combination of metal ions , and organic ligands, , making it possible to prepare appropriate MOFs for specific separation systems. , In addition, several MOFs possess structural flexibility and exhibit structural deformation in response to external stimuli, such as temperature and pressure changes and light exposure. One notable manifestation of these is the adsorption-induced structural transition, commonly referred to as “gate opening” or “breathing,” which sharply increases the amount adsorbed at a threshold gas pressure (gate pressure). − This abrupt change in adsorption renders flexible MOFs useful in various industrial applications.…”

“…Metal−organic frameworks (MOFs) are among the most promising materials for advancing the utilization of adsorbentbased separations. Because of their regular structures and high designability, 3−8 pore sizes and host−guest interactions, which determine the gas selectivity and amount adsorbed, can be controlled by customizing the combination of metal ions 9,10 and organic ligands, 11,12 making it possible to prepare appropriate MOFs for specific separation systems. 13,14 In addition, several MOFs possess structural flexibility and exhibit structural deformation in response to external stimuli, such as temperature and pressure changes and light exposure.…”