Magnetic resonance spectroscopies occupy a premier position within the chemical sciences by revealing structure and dynamics in molecules and solids associated with photosynthesis, enzymology, Alzheimer proteins, pharmaceuticals, catalysts, polymers, and electronic materials. Here, we review the recent literature contributions of NMR and EPR spectroscopy towards the study of metal–organic frameworks from 2017 to mid-2022. We organize the review around what we perceive to be the intellectual challenges in MOF research: structure, dynamics, synthesis, properties, and function.

Luminescent materials with tunable emission are becoming increasingly desirable as we move towards needing efficient Light Emitting Diodes (LEDs) for displays. Key to developing better displays is the advancement of strategies for rationally designing emissive materials that are tunable and efficient. We report a series of emissive metal-organic frameworks (MOFs) generated using BUT-10 (BUT: Beijing University of Technology) that emits green light with λ_max at 525 nm. Post-synthetic reduction of the ketone on the fluorenone ligand in BUT-10 generates new materials, BUT-10-M and BUT-10-R. The emission for BUT-10-R is hypsochromically-shifted by 113 nm. Multivariate BUT-10-M structures demonstrate emission with two maxima corresponding to the emission of both fluorenol and fluorenone moieties present in their structures. Our study represents a novel post-synthetic ligand reduction strategy for producing emissive MOFs with tunable emission ranging from green, white-blue to deep blue.

Abstract: Luminescent materials with tunable emission are becoming increasingly desirable as we move towards needing efficient Light Emitting Diodes (LEDs) for displays. Key to developing better displays is the advancement of strategies for rationally designing emissive materials that are tunable and efficient. We report a series of emissive metal‐organic frameworks (MOFs) generated using BUT‐10 (BUT: Beijing University of Technology) that emits green light with λmax at 525 nm. Post‐synthetic reduction of the ketone on the fluorenone ligand in BUT‐10 generates new materials, BUT‐10‐M and BUT‐10‐R. The emission for BUT‐10‐R is hypsochromically‐shifted by 113 nm. Multivariate BUT‐10‐M structures demonstrate emission with two maxima corresponding to the emission of both fluorenol and fluorenone moieties present in their structures. Our study represents a novel post‐synthetic ligand reduction strategy for producing emissive MOFs with tunable emission ranging from green, white‐blue to deep blue.

The formation and preservation of the active phase of the catalysts at the triple-phase interface during CO₂ capture and reduction is essential for improving the conversion efficiency of CO₂ electroreduction toward value-added chemicals and fuels under operational conditions. Designing such ideal catalysts that can mitigate parasitic hydrogen generation and prevent active phase degradation during the CO₂ reduction reaction (CO₂RR), however, remains a significant challenge. Herein, we developed an interfacial engineering strategy to build a new SnO_x catalyst by invoking multiscale approaches. This catalyst features a hierarchically nanoporous structure coated with an organic F-monolayer that modifies the triple-phase interface in aqueous electrolytes, substantially reducing competing hydrogen generation (less than 5%) and enhancing CO₂RR selectivity (∼90%). This rationally designed triple-phase interface overcomes the issue of limited CO₂ solubility in aqueous electrolytes via proactive CO₂ capture and reduction. Concurrently, we utilized pulsed square-wave potentials to dynamically recover the active phase for the CO₂RR to regulate the production of C1 products such as formate and carbon monoxide (CO). This protocol ensures profoundly enhanced CO₂RR selectivity (∼90%) compared with constant potential (∼70%) applied at -0.8 V (V vs RHE). We further achieved a mechanistic understanding of the CO₂ capture and reduction processes under pulsed square-wave potentials via in situ Raman spectroscopy, thereby observing the potential-dependent intensity of Raman vibrational modes of the active phase and CO₂RR intermediates. This work will inspire material design strategies by leveraging triple-phase interface engineering for emerging electrochemical processes, as technology moves toward electrification and decarbonization.

In nature, nonheme iron enzymes use dioxygen to generate high-spin iron(IV)=O species for a variety of oxygenation reactions. Although synthetic chemists have long sought to mimic this reactivity, the enzyme-like activation of O₂ to form high-spin iron(IV) = O species remains an unrealized goal. Here, we report a metal-organic framework featuring iron(II) sites with a local structure similar to that in α-ketoglutarate-dependent dioxygenases. The framework reacts with O₂ at low temperatures to form high-spin iron(IV) = O species that are characterized using in situ diffuse reflectance infrared Fourier transform, in situ and variable-field Mössbauer, Fe Kβ x-ray emission, and nuclear resonance vibrational spectroscopies. In the presence of O₂, the framework is competent for catalytic oxygenation of cyclohexane and the stoichiometric conversion of ethane to ethanol.