This study presents a comprehensive analysis of the vibrational spectra of methyl-β-D-ribofuranoside. Employing a combination of inelastic neutron scattering, Raman, and infrared spectroscopy allows ...for the observation of all modes regardless of the selection rules. The experimental techniques were complemented by density functional theory computational methods using both gas-phase (Gaussian) and solid-state (CRYSTAL, CASTEP) approaches to provide an unambiguous assignment of the defining vibrational features. Two distinct structures of the molecule were identified in the unit cell, differentiated mainly by the orientation of the furanose ring O–H bonds. The low-energy region of the spectrum (<400 cm–1) is dominated by lattice vibrations and functional group rotation, while the midenergy region is dominated by out-of-plane bending motions of the furanose ring (400–900 cm–1) and by C–H bending in the methyl and methylene groups (1400–1600 cm–1). The high-energy region (>2800 cm–1) encompasses the C–H and O–H stretching modes and offers convincing evidence of at least one H-bonding interaction between the two structures of methyl-β-D-ribofuranoside.
Abstract
Stimuli-responsive behaviors of flexible metal–organic frameworks (MOFs) make these materials promising in a wide variety of applications such as gas separation, drug delivery, and molecular ...sensing. Considerable efforts have been made over the last decade to understand the structural changes of flexible MOFs in response to external stimuli. Uniform pore deformation has been used as the general description. However, recent advances in synthesizing MOFs with non-uniform porous structures, i.e. with multiple types of pores which vary in size, shape, and environment, challenge the adequacy of this description. Here, we demonstrate that the CO
2
-adsorption-stimulated structural change of a flexible MOF, ZIF-7, is induced by CO
2
migration in its non-uniform porous structure rather than by the proactive opening of one type of its guest-hosting pores. Structural dynamics induced by guest migration in non-uniform porous structures is rare among the enormous number of MOFs discovered and detailed characterization is very limited in the literature. The concept presented in this work provides new insights into MOF flexibility.
During nuclear waste disposal process, radioactive iodine as a fission product can be released. The widespread implementation of sustainable nuclear energy thus requires the development of efficient ...iodine stores that have simultaneously high capacity, stability and more importantly, storage density (and hence minimized system volume). Here, we report high I2 adsorption in a series of robust porous metal–organic materials, MFM-300(M) (M = Al, Sc, Fe, In). MFM-300(Sc) exhibits fully reversible I2 uptake of 1.54 g g–1, and its structure remains completely unperturbed upon inclusion/removal of I2. Direct observation and quantification of the adsorption, binding domains and dynamics of guest I2 molecules within these hosts have been achieved using XPS, TGA-MS, high resolution synchrotron X-ray diffraction, pair distribution function analysis, Raman, terahertz and neutron spectroscopy, coupled with density functional theory modeling. These complementary techniques reveal a comprehensive understanding of the host–I2 and I2–I2 binding interactions at a molecular level. The initial binding site of I2 in MFM-300(Sc), I2 I, is located near the bridging hydroxyl group of the ScO4(OH)2 moiety I2 I···H–O = 2.263(9) Å with an occupancy of 0.268. I2 II is located interstitially between two phenyl rings of neighboring ligand molecules I2 II···phenyl ring = 3.378(9) and 4.228(5) Å. I2 II is 4.565(2) Å from the hydroxyl group with an occupancy of 0.208. Significantly, at high I2 loading an unprecedented self-aggregation of I2 molecules into triple-helical chains within the confined nanovoids has been observed at crystallographic resolution, leading to a highly efficient packing of I2 molecules with an exceptional I2 storage density of 3.08 g cm–3 in MFM-300(Sc).
Density of Phonon States in Cubic Ice Ic del Rosso, Leonardo; Celli, Milva; Colognesi, Daniele ...
Journal of physical chemistry. C,
10/2021, Letnik:
125, Številka:
42
Journal Article
Recenzirano
Despite the simplicity of water molecules, for more than a century, a lot of scientific effort has been made on exploring ice polymorphism, especially more elusive phases such as cubic ice Ic. In ...this work, measurement of the density of phonon states (DOPSs) of polycrystalline ice Ic, and of its deuterated counterpart, has been performed in a sample having an almost perfect crystallographic purity, obtained from the transformation of ice XVII, and with a remarkable accuracy. Results are compared with the new accurate measurements of DOPSs in ice Ih and with centroid molecular dynamics (CMD) simulations. The differences between the experimental DOPSs in these two forms of ice are subtle but quantitatively measurable. In addition, they are reproduced semiquantitatively by computational methods, demonstrating the effectiveness of this innovative simulation tool for calculating the dynamical properties of ice structures.
Metal–organic framework (MOF) materials provide an excellent platform to fabricate single-atom catalysts due to their structural diversity, intrinsic porosity, and designable functionality. However, ...the unambiguous identification of atomically dispersed metal sites and the elucidation of their role in catalysis are challenging due to limited methods of characterization and lack of direct structural information. Here, we report a comprehensive investigation of the structure and the role of atomically dispersed copper sites in UiO-66 for the catalytic reduction of NO2 at ambient temperature. The atomic dispersion of copper sites on UiO-66 is confirmed by high-angle annular dark-field scanning transmission electron microscopy, electron paramagnetic resonance spectroscopy, and inelastic neutron scattering, and their location is identified by neutron powder diffraction and solid-state nuclear magnetic resonance spectroscopy. The Cu/UiO-66 catalyst exhibits superior catalytic performance for the reduction of NO2 at 25 °C without the use of reductants. A selectivity of 88% for the formation of N2 at a 97% conversion of NO2 with a lifetime of >50 h and an unprecedented turnover frequency of 6.1 h–1 is achieved under nonthermal plasma activation. In situ and operando infrared, solid-state NMR, and EPR spectroscopy reveal the critical role of copper sites in the adsorption and activation of NO2 molecules, with the formation of {Cu(I)···NO} and {Cu···NO2} adducts promoting the conversion of NO2 to N2. This study will inspire the further design and study of new efficient single-atom catalysts for NO2 abatement via detailed unravelling of their role in catalysis.
The limits of detection (LOD) and quantitation (LOQ) in the mass domain, for broadband vibrational spectroscopy with neutrons on the TOSCA spectrometer at the ISIS Pulsed Neutron and Muon Source ...(UK), have been studied. The well-known 3σ and 10σ approaches are used through a specifically developed analytical procedure that is based on the calculation of the integrated spectral intensities in selected energy-transfer ranges, as a function of mass of standard reference materials and calibrants, such as ZrH2, 2,5-diiodothiophene, and low-density polyethylene. The analysis shows that the blank, that is, the instrument setup without the analyte, plays a critical role in the measurement performance, especially for small specimen quantities. The results point that TOSCA enables detection of 128 μmol (LODH) and quantitation of 428 μmol (LOQH) of elemental hydrogen analytes in ZrH2. The determined values for this and other standards allow for the assessment of the calibration curve design and instrument sensitivity and define a method to be used for inelastic neutron scattering spectrometers such as TOSCA, or VESPA, the new beamline under construction at the European Spallation Source in Lund (Sweden).
The production of MOFs at large scale in a sustainable way is key if these materials are to be exploited for their promised widespread application. Much of the published literature has focused on ...demonstrations of preparation routes using difficult or expensive methodologies to scale. One such MOF is nano-zeolitic imidazolate framework-8 (ZIF-8) - a material of interest for a range of possible applications. Work presented here shows how the synthesis of ZIF-8 can be tracked by a range of methods including X-ray diffraction, thermo gravimetric analysis and inelastic neutron scattering - which offer the prospect of in-line monitoring of the synthesis reaction. Herein we disclose how the production of nano-ZIF-8 can be conducted at scale using the intermediate phase ZIF-L. By understanding the economics and demonstrating the production of 1 kg of nano-ZIF-8 at pilot scale we have shown how this once difficult to make material can be produced to specification in a scalable and cost-efficient fashion.
Incorporation of mesopores and active sites into metal-organic framework (MOF) materials to uncover new efficient catalysts is a highly desirable but challenging task. We report the first example of ...a mesoporous MOF obtained by templated electrosynthesis using an ionic liquid as both electrolyte and template. The mesoporous Cu(II)-MOF MFM-100 has been synthesised in 100 seconds at room temperature, and this material incorporates crystal defects with uncoupled Cu(II) centres as evidenced by confocal fluorescence microscopy and electron paramagnetic resonance spectroscopy. MFM-100 prepared in this way shows exceptional catalytic activity for the aerobic oxidation of alcohols to produce aldehydes in near quantitative yield and selectivity under mild conditions, as well as having excellent stability and reusability over repeated cycles. The catalyst-substrate binding interactions have been probed by inelastic neutron scattering. This study offers a simple strategy to create mesopores and active sites simultaneously via electrochemical formation of crystal defects to promote efficient catalysis using MOFs.
Selective adsorption of SO2 is realized in a porous metal–organic framework material, and in‐depth structural and spectroscopic investigations using X‐rays, infrared, and neutrons define the ...underlying interactions that cause SO2 to bind more strongly than CO2 and N2.
Ammonia (NH3) is a promising energy resource owing to its high hydrogen density. However, its widespread application is restricted by the lack of efficient and corrosion-resistant storage materials. ...Here, we report high NH3 adsorption in a series of robust metal–organic framework (MOF) materials, MFM-300(M) (M = Fe, V, Cr, In). MFM-300(M) (M = Fe, VIII, Cr) show fully reversible capacity for >20 cycles, reaching capacities of 16.1, 15.6, and 14.0 mmol g–1, respectively, at 273 K and 1 bar. Under the same conditions, MFM-300(VIV) exhibits the highest uptake among this series of MOFs of 17.3 mmol g–1. In situ neutron powder diffraction, single-crystal X-ray diffraction, and electron paramagnetic resonance spectroscopy confirm that the redox-active V center enables host–guest charge transfer, with VIV being reduced to VIII and NH3 being oxidized to hydrazine (N2H4). A combination of in situ inelastic neutron scattering and DFT modeling has revealed the binding dynamics of adsorbed NH3 within these MOFs to afford a comprehensive insight into the application of MOF materials to the adsorption and conversion of NH3.
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