Electron paramagnetic resonance (EPR) spectroscopy is a powerful method to characterize the local framework structure of nanoporous materials during the dihydrogen isotopologue adsorption process. It also allows for exploring the adsorption sites of the dihydrogen isotopes and monitoring their desorption characteristics on the microscopic scale. The paramagnetic spin probes in the form of transition metal ions or organic radicals are required for EPR spectroscopy and are introduced either at the framework lattice position or in the pores of the metal-organic frameworks. This review highlights current advancements within the field of dihydrogen isotopologue detection as well as key findings related to the versatility of in situ continuous wave EPR and pulsed EPR experiments as toolkits for monitoring the adsorption-desorption process of dihydrogen isotopologues from the perspective of the framework as well as studying the host-guest interactions based on high-resolution advantages offered by using a pulsed EPR approach.

The development of smart materials capable of separating dihydrogen isotopologues has risen recently. Among potential candidates, the flexible MIL-53 (Al) has been gaining attention due to its structural flexibility providing the so-called ''breathing mechanism'' that can be useful to separate hydrogen isotopologues selectively. In the present work, an in situ continuous wave electron paramagnetic resonance investigation has been proven as a sensitive technique to follow the isotopologue-selective adsorption-desorption of dihydrogen species on the paramagnetic metal-doped MIL-53 (Al0.99Cr0.01) and MIL-53 (Al0.99V0.01), respectively. The presence of paramagnetic spin probes such as Cr3+ and V4+ inside the MIL-53 framework allows for monitoring the framework transition including the 2nd transition step that selectively occurs at p>100 mbar when D2 gas is adsorbed on the pores at 23 K. Furthermore, investigation of D2 desorption from MIL-53 (Al0.99V0.01) by temperature-dependent hyperfine spectroscopy provides a more detailed analysis of the D2 desorption process on a microscopic scale with respect to the embedded spin probe.

We utilize a 10 MeV electron beam to tune the nitrogen vacancy (NV) center concentration in five diamond samples with similar initial substitutional nitrogen (P1) concentration. We observe inhomogeneous defect distributions of P1, NV and NVN defects by Fourier-transform infrared spectroscopy, electron paramagnetic resonance spectroscopy, confocal photoluminescence scans and polarized light microscopy. Furthermore, we perform field cycling NMR experiments to measure the bulk 13C hyperpolarization of each sample. For that purpose, we exploit the NV-P1 and NV-NV cross-relaxation to transfer the electronic polarization of the NV centers to nearby 13C spins. We found different dependencies of the hyperpolarization signal for NV-P1 and NV-NV cross-relaxation. We propose that dense P1 clusters and the interplay between the defects within are crucial for NV-driven nuclear hyperpolarization.

Multifrequency electron paramagnetic resonance (EPR) methodologies combined with density functional theory (DFT) modeling are used to monitor the local structure of cupric ions doped into a porous zeolitic imidazolate framework (ZIF-8). Because of the constraint imposed by the ZIF-8 framework, Cu2+ ions substituting Zn2+ sites assume a highly distorted tetrahedral geometry. The N-14 electron nuclear double resonance (ENDOR) and hyperfine sublevel correlation (HYSCORE) experiments confirm the incorporation of copper ions in the framework position, providing the first detailed electronic and structural analysis of cupric ions in ZIF materials. The experimental findings are validated by DFT modeling which gives an atomistic picture of the Cu2+-doped material.

Flavin mononucleotide (FMN) is a ubiquitous blue-light pigment due to its ability to drive one- and two-electron transfer reactions. In both light-oxygen-voltage (LOV) domains of phototropin from the green algae Chlamydomonas reinhardtii, FMN is noncovalently bound. In the LOV1 cysteine-to-serine mutant (C57S), light-induced electron transfer from a nearby tryptophan occurs, and a transient spin-correlated radical pair (SCRP) is formed. Within this photocycle, nuclear hyperpolarization is created by the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect. In a side reaction, a stable protonated semiquinone radical (FMNH·) forms undergoing a significant bathochromic shift of the first electronic transition from 445 to 591 nm. The incorporation of phototropin LOV1-C57S into an amorphous trehalose matrix, stabilizing the radical, allows for application of various magnetic resonance experiments at ambient temperatures, which are combined with quantum-chemical calculations. As a result, the bathochromic shift of the first absorption band is explained by lifting the degeneracy of the molecular orbital energy levels for electrons with alpha and beta spins in FMNH· due to the additional electron.

Synthesis and characterization of DEMOFs (defect-engineered metal-organic frameworks) with coordinatively unsaturated sites (CUSs) for gas adsorption, catalysis, and separation are reported. We use the mixed-linker approach to introduce defects in Cu2-paddle wheel units of MOFs [Cu2(Me-trz-ia)2] by replacing up to 7% of the 3-methyl-triazolyl isophthalate linker (1L2-) with the "defective linker" 3-methyl-triazolyl m-benzoate (2L-), causing uncoordinated equatorial sites. PXRD of DEMOFs shows broadened reflections; IR and Raman analysis demonstrates only marginal changes as compared to the regular MOF (ReMOF, without a defective linker). The concentration of the integrated defective linker in DEMOFs is determined by 1H NMR and HPLC, while PXRD patterns reveal that DEMOFs maintain phase purity and crystallinity. Combined XPS (X-ray photoelectron spectroscopy) and cw EPR (continuous wave electron paramagnetic resonance) spectroscopy analyses provide insights into the local structure of defective sites and charge balance, suggesting the presence of two types of defects. Notably, an increase in CuI concentration is observed with incorporation of defective linkers, correlating with the elevated isosteric heat of adsorption (ΔHads). Overall, this approach offers valuable insights into the creation and evolution of CUSs within MOFs through the integration of defective linkers.

The flexibility of the MIL-53(M) metal–organic framework (MOF) has been elucidated through EPR spectroscopy, in liquid adsorption processes.

ERI and SSZ-13 were subjected to post-synthetic treatments (depending on the zeolite topology) to create micro-/mesoporous materials. The results in terms of NH3-SCR-DeNOx show that the applied treatments improved the catalytic activity of the Cu-containing ERI-based materials; however, the NO conversion did not vary for the different materials treated with NaOH or NaOH/HNO3. For the micro-/mesoporous Cu-containing SSZ-13, a lower NO conversion in NH3-SCR-DeNOx was observed. Thus, our findings challenge the current paradigm of enhanced activity of micro-/mesoporous catalysts in NH3-SCR-DeNOx. The modification of the supports results in the presence of different amounts and kinds of copper species (especially isolated Cu2+ and aggregated Cu species) in the case of ERI- and SSZ-13-based samples. The present copper species further differentiate the formation of reactive reaction intermediates. Our studies show that besides the μ-η2,η2-peroxo dicopper(II) complexes (verified by in situ DR UV-Vis spectroscopy), copper nitrates (evidenced by in situ FT-IR spectroscopy) also act as reactive intermediates in these catalytic systems.

The phase-pure zeolite Y with a high n(Si)/n(Al) ratio is obtained with the cyclic polyether 15-Crown-5 as a structure-directing agent. In copper-exchanged for this new zeolite outperformed other Cu-containing zeolite Y counterparts during NH3-SCR-DeNOx with more than 80% NO conversion and more than 85% N2 selectivity in the temperature range of 100 – 500 °C. The presence of Cu+ species located in sodalite cages with elevated redox cyclability guarantees high activity and N2 selectivity up to 400 °C over CuY-Crown. Above 400 °C, a high activity and N2 selectivity are related to the accessibility of chemisorbed NH3 to the gaseous NO during the NH3-SCR-DeNOx.

Commercial SSZ-13 zeolite with different n(Si)/n(Al) ratios and from different suppliers were subjected to a post-synthetic treatment in order to create mesopores of up to 15 nm. Furthermore, the materials were modified with copper ions and thoroughly physico-chemically characterized. The modified textural properties varied the nature of copper species, and thus, activity in the selective catalytic reduction of NOx with ammonia (NH3-SCR-DeNOx). Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) studies with hexane as probe liquid revealed improved intracrystalline diffusion for some Cu-containing SSZ-13 materials. The NH3-SCR-DeNOx pathways are verified via in situ DR UV-Vis, in situ FT-IR and EPR, temperature-programmed studies as well as SSITKA studies that provide a mechanistic understanding of the reaction. Kinetic modelling results demonstrate the highest NH3-SCR-DeNOx reaction rates and up to 20 % lower energy barriers with n(Si)/n(Al) ratio of 6.5 for all modified forms (i. e., (NH4)Cu-SSZ-13_6.5 and Cu-SSZ-13_6.5_NaOH/0.1) and cause only negligible parasitic ammonia oxidation. The modelling of the stop-flow experiments further demonstrates that the SCR pathway via the HONO surface intermediate is present but barely contributes to the overall NO conversion compared to the dominant path between adsorbed NH3 and NO from the gas phase.

Commercial zeolite Y with different n(Si)/n(Al) ratios modified with copper cations were evaluated in the selective catalytic reduction of nitrogen oxide with ammonia (NH3-SCR-DeNO(x)). Among the investigated catalysts, the highest activity was achieved over CuY_CBV100 with 7.7 wt % of Cu. The activity of this sample was further confirmed in the feed of the tail gases stream from the pilot HNO3 plant. The highest N-2 selectivity possesses CuY_CBV500 (3.7 wt % of Cu). To improve catalytic properties, both zeolites were mixed before ion exchange with copper, as well as in a more effective approach, both Cu-containing catalysts were physically mixed (in different weight ratios, 1:1, 1:9, 3:7, 7:3). CuY_CBV100 is more active due to the presence of more active sites, available in reduction/oxidation half-cycles.

The development of tailor-made electrochromic (EC) materials requires a large variety of available substances with properties that precisely match the task. Since the inception of electrochromic metal-organic frameworks (MOFs), the field relies only on a limited set of building blocks, providing the desired electrochromic effect. Herein, we demonstrate for the first time the implementation of a Piccard-type system (N,N,N',N'-benzidinetetrabenzoate) into Zr-MOFs to obtain electrochromic materials. With fast switching rates, high contrast ratio, long-life stability, and exceptional chemical and physical stability, the novel material is on par with inorganic EC material. The new EC system exhibits an ultrahigh contrast from the bleaching state, with transmittance in the visible region >53%, to the colored state with a transmittance of ca. 3%. The 5 μm thick film attained up to 90% of the coloring in 12.5 s and exhibited high electrochemical reversibility. Moreover, the conformational lability of the electrochromic ligand chosen is locked via the topology design of the framework, which is not attainable in the solution. Locked conformations of the redox active linker in distinct polymorphous frameworks (DUT-65 and DUT-66) feature different redox characteristics and opens the door to the overarching control of the oxidation pathway in the Piccard-type systems.

DUT-49(Cu) is a well-studied representative of flexible mesoporous frameworks, in particular, famous for long-lived overloaded metastable states in the presence of a variety of gases at defined temperatures, leading to "negative gas adsorption" transitions. Important mechanistic insights into these transitions in DUT-49 were obtained via in situ powder X-ray diffraction (PXRD) studies conducted in parallel to gas physisorption. However, for strongly X-ray absorbing probe molecules, such as xenon, such studies are not feasible, even if synchrotron radiation is used. Here we employ in situ electron paramagnetic resonance spectroscopy (EPR), PXRD, and adsorption isotherm measurements to explore the phase transformations in DUT-49(Cu) in the presence of xenon and compare its properties with the corresponding adsorption/desorption behavior of ethylene for this material. The antiferromagnetically coupled CuII-CuII dimers in the paddle-wheel (PW) units of this pillared layer MOF serve as local magnetic probes in the in situ EPR measurement. These experiments allowed us to monitor the op <-> cp phase transformations during the xenon physisorption through the structural changes at the PW units encoded in the zero-field splitting parameters of the S = 1 state of the CuII dimers. The EPR data indicates an expansion of the unit cell for the cp phase in the presence of xenon. This novel EPR-derived insight into the phase transformation phenomena of the xenon-loaded DUT-49(Cu) could be validated by combined in situ EPR, PRXD, and adsorption isotherm measurements for ethylene adsorption over the same MOF material in a comparable temperature range.

Herein, electron paramagnetic resonance (EPR) spectroscopy at X- (9.4 GHz), Q- (34 GHz) and W-band (95 GHz), and superconducting quantum interference device (SQUID) measurements on antiferromagnetically coupled metal trimers in MIL-101(Cr) and MIL-100(Al_{0.8}0.8Cr_{0.2}0.2) MOFs were investigated. At low temperatures, the Cr(III) trimers exhibit a Dzyaloshinsky-Moriya (D-M) interaction, and have a total spin state S_T = 1/2T=1/2.

DUT-49(Cu) is a well-studied representative of flexible mesoporous frameworks, in particular, famous for long-lived overloaded metastable states in the presence of a variety of gases at defined temperatures, leading to "negative gas adsorption" transitions. Important mechanistic insights into these transitions in DUT-49 were obtained via in situ powder X-ray diffraction (PXRD) studies conducted in parallel to gas physisorption. However, for strongly X-ray absorbing probe molecules, such as xenon, such studies are not feasible, even if synchrotron radiation is used. Here we employ in situ electron paramagnetic resonance spectroscopy (EPR), PXRD, and adsorption isotherm measurements to explore the phase transformations in DUT-49(Cu) in the presence of xenon and compare its properties with the corresponding adsorption/desorption behavior of ethylene for this material. The antiferromagnetically coupled CuII–CuII dimers in the paddle-wheel (PW) units of this pillared layer MOF serve as local magnetic probes in the in situ EPR measurement. These experiments allowed us to monitor the op ↔ cp phase transformations during the xenon physisorption through the structural changes at the PW units encoded in the zero-field splitting parameters of the S = 1 state of the CuII dimers. The EPR data indicates an expansion of the unit cell for the cp phase in the presence of xenon. This novel EPR-derived insight into the phase transformation phenomena of the xenon-loaded DUT-49(Cu) could be validated by combined in situ EPR, PRXD, and adsorption isotherm measurements for ethylene adsorption over the same MOF material in a comparable temperature range.

In situ continuous wave electron paramagnetic resonance investigation has been proven as a powerful method by employing paramagnetic Ni2+-Co2+ pairs as spin probes to follow the isotope-selective gate opening phenomenon on the DUT-8(Ni-0.98 Co-0.02) framework. This method is very sensitive to detect the phase transition from the closed pore to the open pore phase in response to D-2 adsorption in the framework, while no phase transformation has been observed during H-2 gas adsorption. More interestingly, it is also able to sense local structural changes around the spin probe during the desorption of D-2 gas. Based on these evidences, the in situ continuous wave electron paramagnetic resonance method can be implemented as an efficient and non-invasive technique for the detection of dihydrogen isotopes.

ERI, SSZ-13, and ZSM-5 were subjected to post-synthetic treatments (depending on the zeolite topology) to create micro-/mesoporous materials. The results of NH3-SCR-DeNOx show that the post-synthetic treatments improved the catalytic activity of the Cu-containing ERI-based materials, however, the NO conversion does not vary for the different materials treated with NaOH or NaOH/HNO3. For the Cu-containing SSZ-13 and ZSM-5, a lower NO conversion or no changes in NH3-SCR-DeNOx, respectively, are observed. The modification of the supports results in the presence of different amount and kind of copper species (especially isolated Cu2+ and aggregated Cu species) in the case of ERI- and SSZ-13-based samples. The activity of the catalysts is correlated with the formation of nitrates determined by applying in situ FT-IR. While the formation of μ-η2,η2-peroxo dicopper(II) intermediate is hampered at low temperatures in the presence of micro-/mesoporous Cu-SSZ-13 material, leading to its lower activity as compared to conventional Cu-SSZ-13.

Description of the dataset: Data type: Experimental spectroscopic measurements Files are with filename extensions: spc, par, txt and opj Information on origin of the data: EPR spectroscopic measurements with filename extensions spc, par, txt and opj. Data visualisation was conducted using OriginLab version 8. X-band CW-EPR spectroscopic measurements were generated by EMX spectrometer equipped with SHQ cavity produced by Bruker. Four different folders indicates full in situ EPR data during adsorption and desorption of dihydrogen isotope (H2 and D2) Additional Information : specialized abbreviations: EPR – Electron Paramagnetic Resonance, DUT – Dresden University Technology definitions of variables: Magnetic field, Pressures, Microwave power. units of measurement: Gauss (G), milliTesla (mT), millibar(mbar), microwave power (dB). abbreviations on the data filename: Dates, Sample name, H2/D2 ads/des (ads= adsorption, des=desorption), microwave power, Pressures, number scans if indicated.

Data type: Experimental spectroscopic measurements, computer simulation and analysis Files are with filename extensions: DSC, DAT, m, txt Information on origin of the data: EPR spectroscopic measurements with filename extensions DSC, DTA. EPR spectroscopic simulation and analyses with filename extension m. EPR spectra are exported as txt files in ASCII format. X-band CW-EPR spectroscopic measurements were generated by EMX spectrometer equipped with SHQ cavity produced by Bruker. If the dataset includes multiple files that relate to each other: Files in PARACAT_WP4_20201111_ULEI_21_DUT49Mn@7K folder includes X-band CW-EPR spectroscopic measurements; original data are in DTA/DSC and txt formats. Files in PARACAT_WP4_20201111_ULEI_00_DUT49Mn@simulation folder includes computer simulations/analyses of the EPR measurements; data are in m and txt formats. Information on: specialized abbreviations: DUT49Cu – DUT-49(Cu) MOF, DUT49Mn – DUT-49(Mn) MOF, DUT49CuZn – DUT-49(CuZn) MOF, DUT49MnCu – DUT-49(MnCu) MOF. @10K – measured at 10 K definitions of variables: Magnetic field, Temperature. units of measurement: Gauss (G), K, degree (°), milliTesla (mT).