Unraveling Structure and Dynamics in Porous Frameworks via Advanced In Situ Characterization Techniques

Abstract

Dynamic metal-organic frameworks (MOFs) represent a subgroup of frameworks featuring unique performance, as they are capable of adapting their pore size and/or the orientation of framework constituents in response to specific guest molecules such as gases or solutes and often outperform their rigid analogus in gas storage, sensing, or separation. In this review, the authors focus on recent methodical developments of advanced in situ diffraction and spectroscopic techniques for comprehensive characterization of porous frameworks. Examples for advanced instrumentation are highlighted for in situ nuclear magnetic resonance, electron paramagnetic resonance, and optical spectroscopies as well as X-ray and neutron diffraction. Several examples of high-resolution transmission electron microscopy (HRTEM) on MOFs are shown because HRTEM is an emerging technique for the characterization of time-resolved structural dynamics in MOFs. These methods shed light on structural features and phase transitions of the host, its spin state, electronic structure, specific host-guest and guest-guest interactions, preferable adsorption sites, and bonding situation in the framework, focusing on the most prominent recent case studies. The synergistic development of novel in situ characterization methods and exploration of well-defined model framework systems are crucial to advance the understanding of dynamic processes in porous materials in future.

Chemistry of Soft Porous Crystals: Structural Dynamics and Gas Adsorption Properties

“…The structural complexity, stimuli‐responsiveness, and global and local dynamics complicate the predictive synthesis and in‐depth characterization of SPCs and their guest–host properties. However, the increasing accessibility and accuracy of in situ experimental techniques makes it possible to study the dynamics and transitions alongside the adsorption of gases, vapors, and liquids in previously unattained detail . In particular, the recent progress in developing computational tools suitable for studying large systems allows postulating mechanisms even for the most unusual phenomena.…”

“…In particular, for guest‐induced transitions, in situ characterization of the global and local structural properties of SPCs is essential. The in situ X‐ray crystallographic analysis of powders and single crystals and the adsorption/desorption of gases, vapors, and liquids are established techniques for probing structural changes . In recent years, the importance of structural features beyond the molecular level in SPCs was highlighted .…”

Influence of Thermal and Mechanical Stimuli on the Behavior of Al-CAU-13 Metal–Organic Framework

“…Prior to its further use for an application, significant effort must be devoted to the characterization of the thermal and mechanical stability of MOFs [ 41 , 42 ]. Flexible MOFs in particular have been intensively investigated [ 43 , 44 ]. MIL-53 (MIL: Materiaux Institut Lavoisier, Versailles, France) in particular has attracted much attention, due to the so-called breathing effect, facilitated by the structure’s wine-rack topology of 1D lozenge-shaped channels [ 45 ].…”

Massive Pressure Amplification by Stimulated Contraction of Mesoporous Frameworks

“…To investigate potential framework transitions in the adsorption process, the physisorption of CO2 on DUT-46 and DUT-49 was analyzed by advanced in situ X-ray powder diffraction at KMC-2 beamline of the BESSY-II synchrotron in parallel to the adsorption and desorption of CO2 at 195 K (Figure 3). [41] Both frameworks feature pronounced structural transition at a distinct relative pressures (0.45 for DUT-46 and 0.50 for DUT-49). In case of DUT-46, the isotherm measured in situ shows an additional step at p/p0 = 0.9 and a second hysteresis, absent in the ex situ experiment.…”