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Dysprosium(III)-containing single-molecule magnets (SMMs) show blocking of the molecular magnetization and hysteresis effects in one molecule. They belong to the class of the best performing SMMs at present. Here, we present first results of 161Dy-Nuclear Resonance Vibrational Spectroscopy (NRVS) experiments on the dysprosium(III) complex [Dy(H2dapp)(NO3)2](NO3) with H2dapp being 2,6-bis((E)-1-(2-(pyridine-2-yl)-hydrazineylidene)ethyl)pyridine. For the 161Dy-NRVS experiments a compact novel He flow cryostat was used at the Advanced Photon Source, Argonne National Laboratories, which enables low temperature NRVS experiments in helium vapour circumventing the often-observed difference between sensor read and "real" sample temperature in mostly used LHe and/or closed cycle cryostats with the NRVS sample being in vacuum. To explore the vibrational modes of the molecule simulations based on first density functional theory (DFT) calculations are presented. [ABSTRACT FROM AUTHOR]

Hydroxylation of wadsleyite, β-(Mg,Fe)2SiO4, is associated with divalent cation defects and well known to afect its physical properties. However, an atomic-scale understanding of the defect structure and hydrogen bonding at high pressures is needed to interpret the influence of water on the behavior of wadsleyite in the mantle transition zone. We have determined the pressure evolution of the wadsleyite crystal symmetry and structure, including all O∙∙∙O interatomic distances, up to 32 GPa using single-crystal X-ray difraction on two well-characterized, Fe-bearing (Fo90) samples containing 0.25(4) and 2.0(2) wt% H2O. Both compositions undergo a pressure-dependent monoclinic distortion from orthorhombic symmetry above 9 GPa, with the less hydrous sample showing a larger increase in distortion at increased pressures due to the diference in compressibility of the split M3 site in the monoclinic setting arising from preferred vacancy ordering at the M3B site. Although hydrogen positions cannot be modeled from the X-ray difraction data, the pressure evolution of the longer O1∙∙∙O4 distance in the structure characterizes the primary hydrogen bond length. We observe the hydrogen-bonded O1∙∙∙O4 distance shorten gradually from 3.080(1) Å at ambient pressure to about 2.90(1) Å at 25 GPa, being still much longer than is defined as strong hydrogen bonding (2.5–2.7 Å). Above 25 GPa and up to the maximum pressure of the experiment at 32.5 GPa, the hydrogen-bonded O1∙∙∙O4 distance decreases no further, despite the fact that previous spectroscopic studies have shown that the primary O-H stretching frequencies continuously drop into the regime of strong hydrogen bonding (<3200 cm–1) above ~15 GPa. We propose that the primary O1-H∙∙∙O4 hydrogen bond in wadsleyite becomes highly nonlinear at high pressures based on its deviation from frequency-distance correlations for linear hydrogen bonds. One possible explanation is that the hydrogen position shifts from being nearly on the long O1-O4 edge of the M3 site to a position more above O1 along the c-axis. [ABSTRACT FROM AUTHOR]

We have performed and analyzed the first combined 151Eu and 57Fe nuclear resonant vibrational spectroscopy (NRVS) for naturally abundant KEu(III)[Fe(II)(CN)6] and Eu(III)[Fe(III)(CN)6] complexes. Comparison of the observed 151Eu vs.57Fe NRVS spectroscopic features confirms that Eu(III) in both KEu(III)[Fe(II)(CN)6] and Eu(III)[Fe(III)(CN)6] occupies a position outside the [Fe(CN)6] core and coordinates to the N atoms of the CN− ions, whereas Fe(III) or Fe(II) occupies the site inside the [Fe(CN)6]4− core and coordinates to the C atoms of the CN− ions. In addition to the spectroscopic interest, the results from this study provide invaluable insights for the design and evaluation of the nanoparticles of such complexes as potential cellular contrast agents for their use in magnetic resonance imaging. The combined 151Eu and 57Fe NRVS measurements are also among the first few explorations of bi-isotopic NRVS experiments. [ABSTRACT FROM AUTHOR]

Jeffbenite, ideally Mg3Al2Si3O12, has been identified as inclusions in super-deep diamonds originating from depths that exceed 300 km. Although Mg-end member jeffbenite has limited stability at upper-mantle conditions, iron-bearing jeffbenite may have broader P–T stability that extends to the transition zone or uppermost lower mantle, incorporating significant amounts of ferric iron. Using synchrotron-based, single-crystal X-ray diffraction (XRD) and synchrotron Mössbauer spectroscopy (SMS) at pressures up to 29 GPa, we report the crystal structure, compressibility, and likely spin transition of iron in ferromagnesian jeffbenite (Mg2.32Al0.03Fe2+1.28Fe3+1.77Si2.85O12). High-pressure structure refinements reveal that Fe3+ substitution for Si in the T2 site, which shares edges with the M2 octahedron, likely stabilizes jeffbenite at high pressure, because it increases the cation-to-cation distance between these sites. Although ferromagnesian jeffbenite does not undergo a structural phase transition below 30 GPa, SMS hyperfine parameters suggest the onset of an electronic spin transition of iron from high-spin (HS) to low-spin (LS) at around 22 GPa, which may increase its stability at high pressures. Pressure–volume data were fit to a third order Birch–Murnaghan equation of state, resulting in V0 = 816.54(9), KT0 = 181.54(1.39), and K T 0 ′ = 2.76(14). These equation of state parameters are applicable to evaluating the encapsulation pressures of super-deep diamonds. The density and bulk modulus of ferromagnesian jeffbenite are similar to or higher than pyrope–almandine, pyrope–majorite, and skiagite–majorite solid solution garnets, further suggesting that jeffbenite may be an important ferric–iron silicate in the deeper parts of the mantle transition zone and uppermost lower mantle. However, future studies on the influence of temperature and oxidation state on the stability and equations of state of iron-bearing jeffbennite are still needed to determine what role, if any, jeffbenite plays in transition-zone mineralogy. [ABSTRACT FROM AUTHOR]

Operando nuclear resonant inelastic X‐ray scattering (NRIXS) and X‐ray absorption fine‐structure spectroscopy (XAFS) measurements were used to gain insight into the structure and surface composition of FeCu and FeAg nanoparticles (NPs) during the electrochemical CO2 reduction (CO2RR) and to extract correlations with their catalytic activity and selectivity. The formation of a core–shell structure during CO2RR for FeAg NPs was inferred from the analysis of the operando NRIXS data (phonon density of states, PDOS) and XAFS measurements. Electrochemical analysis of the FeAg NPs revealed a faradaic selectivity of 36 % for CO in 0.1 M KHCO3 at −1.1 V vs. RHE, similar to that of pure Ag NPs. In contrast, a predominant selectivity towards H2 evolution is obtained in the case of the FeCu NPs, analogous to the results obtained for pure Fe NPs, although small Cu NPs have also been shown to favor H2 production. [ABSTRACT FROM AUTHOR]

Operando nuclear resonant inelastic X‐ray scattering (NRIXS) and X‐ray absorption fine‐structure spectroscopy (XAFS) measurements were used to gain insight into the structure and surface composition of FeCu and FeAg nanoparticles (NPs) during the electrochemical CO2 reduction (CO2RR) and to extract correlations with their catalytic activity and selectivity. The formation of a core–shell structure during CO2RR for FeAg NPs was inferred from the analysis of the operando NRIXS data (phonon density of states, PDOS) and XAFS measurements. Electrochemical analysis of the FeAg NPs revealed a faradaic selectivity of 36 % for CO in 0.1 M KHCO3 at −1.1 V vs. RHE, similar to that of pure Ag NPs. In contrast, a predominant selectivity towards H2 evolution is obtained in the case of the FeCu NPs, analogous to the results obtained for pure Fe NPs, although small Cu NPs have also been shown to favor H2 production. [ABSTRACT FROM AUTHOR]

Inelastic X‐ray scattering is a powerful and versatile technique for studying lattice dynamics in materials of scientific and technological importance. In this article, the design and capabilities of the momentum‐resolved high‐energy‐resolution inelastic X‐ray spectrometer (HERIX) at beamline 30‐ID of the Advanced Photon Source are reported. The instrument operates at 23.724 keV and has an energy resolution of 1.3–1.7 meV. It can accommodate momentum transfers of up to 72 nm−1, at a typical X‐ray flux of 4.5 × 109 photons s−1 meV−1 at the sample. A suite of in situ sample environments are provided, including high pressure, static magnetic fields and uniaxial strains, all at high or cryogenic temperatures. [ABSTRACT FROM AUTHOR]

The phonon propagation and damping along the axial direction of films of aligned 40 wt % calf-thymus DNA rods are studied by inelastic x-ray scattering (IXS). The IXS spectra are analyzed with the generalized three effective eigenmode theory, from which we extract the dynamic structure factor S(Q,E) as a function of transferred energy E=hω, and the magnitude of the transferred wave vector Q. S(Q,E) of a DNA sample typically consists of three peaks, one central Rayleigh scattering peak, and two symmetric Stokes and anti-Stokes Brillouin side peaks. By analyzing the Brillouin peaks, the phonon excitation energy and damping can be extracted at different Q values from about 4 to 30 nm-1. A high-frequency sound speed is obtained from the initial slope of the linear portion of the dispersion relation below Q=4 nm-1. The high-frequency sound speed obtained in this Q range is 3100 m/s, which is about twice faster than the ultrasound speed of 1800 m/s, measured by Brillouin light scattering at Q∼0.01 nm-1 at the similar hydration level. Our observations provide further evidence of the strong coupling between the internal dynamics of a DNA molecule and the dynamics of the solvent. The effect on damping and propagation of phonons along the axial direction of DNA rods due to divalent and trivalent counterions has been studied. It is found that the added multivalent counterions introduce stronger phonon damping. The phonons at the range between ∼12.5 and ∼22.5 nm-1 are overdamped by the added counterions according to our model analyses. The intermediate scattering function is extracted and it shows a clear two-step relaxation with the fast relaxation time ranging from 0.1 to 4 ps. [ABSTRACT FROM AUTHOR]

The reaction of protein-bound iron-sulfur (Fe-S) clusters with nitric oxide (NO) plays key roles in NO-mediated toxicity and signaling. Elucidation of the mechanism of the reaction of NO with DNA regulatory proteins that contain Fe-S clusters has been hampered by a lack of information about the nature of the iron-nitrosyl products formed. Herein, we report nuclear resonance vibrational spectroscopy (NRVS) and density functional theory (DFT) calculations that identify NO reaction products in WhiD and NsrR, regulatory proteins that use a [4Fe-4S] cluster to sense NO. This work reveals that nitrosylation yields multiple products structurally related to Roussin's Red Ester (RRE, [Fe2(NO)4(Cys)2]) and Roussin's Black Salt (RBS, [Fe4(NO)7S3]. In the latter case, the absence of 32S/34S shifts in the Fe−S region of the NRVS spectra suggest that a new species, Roussin's Black Ester (RBE), may be formed, in which one or more of the sulfide ligands is replaced by Cys thiolates. [ABSTRACT FROM AUTHOR]

The reaction of protein-bound iron-sulfur (Fe-S) clusters with nitric oxide (NO) plays key roles in NO-mediated toxicity and signaling. Elucidation of the mechanism of the reaction of NO with DNA regulatory proteins that contain Fe-S clusters has been hampered by a lack of information about the nature of the iron-nitrosyl products formed. Herein, we report nuclear resonance vibrational spectroscopy (NRVS) and density functional theory (DFT) calculations that identify NO reaction products in WhiD and NsrR, regulatory proteins that use a [4Fe-4S] cluster to sense NO. This work reveals that nitrosylation yields multiple products structurally related to Roussin's Red Ester (RRE, [Fe2(NO)4(Cys)2]) and Roussin's Black Salt (RBS, [Fe4(NO)7S3]. In the latter case, the absence of 32S/34S shifts in the Fe−S region of the NRVS spectra suggest that a new species, Roussin's Black Ester (RBE), may be formed, in which one or more of the sulfide ligands is replaced by Cys thiolates. [ABSTRACT FROM AUTHOR]

We have applied 57Fe nuclear resonance vibrational spectroscopy (NRVS) for the first time to study the dynamics of Fe centers in Iron-sulfur protein crystals, including oxidized wild type rubredoxin crystals from Pyrococcus furiosus, and the MoFe protein of nitrogenase from Azotobacter vinelandii. Thanks to the NRVS selection rule, selectively probed vibrational modes have been observed in both oriented rubredoxin and MoFe protein crystals. The NRVS work was complemented by extended X-ray absorption fine structure spectroscopy (EXAFS) measurements on oxidized wild type rubredoxin crystals from Pyrococcus furiosus. The EXAFS spectra revealed the Fe-S bond length difference in oxidized Pf Rd protein, which is qualitatively consistent with the crystal structure. [ABSTRACT FROM AUTHOR]

Nuclear inelastic scattering of 57Fe labeled [NiFe] hydrogenase is shown to give information on different states of the enzyme. It was thus possible to detect and assign FeCO and FeCN bending and stretching vibrations of the active site outside the spectral range of the FeS cluster normal modes. [ABSTRACT FROM AUTHOR]

Blick ins Zentrum: Die Methode der inelastischen kernresonanten Streuung (NRVS) wurde genutzt, um 57Fe ‐ markierte [NiFe] ‐ Hydrogenase in unterschiedlichen Zuständen des Enzyms zu untersuchen. Damit gelang es, die Fe ‐ CO ‐ und Fe ‐ CN ‐ Beuge ‐ und ‐ Streckschwingung außerhalb des Spektralbereichs der Normalmoden der Fe ‐ S ‐ Cluster zu detektieren und zuzuordnen (siehe Spektrum). [ABSTRACT FROM AUTHOR]

The electronic spin and valence states of iron in lower-mantle silicate perovskite have been previously investigated at high pressures using various experimental and theoretical techniques. However, experimental results and their interpretation remain highly debated. Here we have studied a well-characterized silicate perovskite starting sample [(Mg0.9,Fe0.1)SiO3] in a chemically inert Ne pressure medium at pressures up to 120 GPa using synchrotron Mössbauer spectra. Analyses of the Mössbauer spectra explicitly show a high-spin to low-spin transition of the octahedral-site Fe3+ occurring at ~13--24 GPa, as evidenced from a significant increase in the hyperfine quadrupole splitting. Two quadrupole doublets of the A-site Fe2+, with extremely high-QS values of 4.1 and 3.1 mm/s, occur simultaneously with the spin transition of the octahedral-site Fe3+ and continue to develop to 120 GPa. It is conceivable that the spin-pairing transition of the octahedral-site Fe3+ causes a volume reduction and a change in the local atomic-site configurations that result in a significant increase of the quadrupole splitting in the dodecahedral-site Fe2+ at 13--24 GPa. Our results here provide a coherent explanation for recent experimental and theoretical results on the spin and valence states of iron in perovskite, and assist in comprehending the effects of the spin and valence states of iron on the properties of the lower-mantle minerals. [ABSTRACT FROM AUTHOR]

Pressure, together with temperature, composition, or external fields, alone or in combination, can be used as principal variables in directing and controlling matter as well as for the synthesis of revolutionary new materials. The impact of extreme conditions to science, however, has been previously limited by the available vessels and probes. The last decade has witnessed a significant surge in extreme conditions science, thanks to the development of in situ synchrotron radiation (SR) probes and high-pressure (HP) instrumentation. Extreme conditions directly alter chemical, structural, mechanical, electronic, magnetic, and phonon properties of materials, revealing intriguing behaviors across boundaries between insulators and metals, ferromagnets and superconductors, ordered and disordered, and vigorously reactive and inert compounds. In Earth and planetary sciences, research from simulating experiments at high pressure and high temperature provides key information in understanding processes, dynamics, and formation of the deep interiors. For materials applications such as the search for new energy materials and superhard materials, extreme conditions remain a vast, unexplored field. [ABSTRACT FROM AUTHOR]

This article reports that a group from the University of Michigan, Ann Arbor, Michigan directly measured the transient strain in an ultrafast laser-excited germanium single crystal using time-resolved X-ray anomalous transmission at the MHATT/XOR sector 7-ID undulator beamline. Scientific research in the time domain using the pulsed structure of the X-ray beams from a third-generation synchrotron source, such as the Advanced Photon Source has become a major interest among synchrotron users. The traditional materials science, chemistry, and biology communities are getting an early glimpse of the potential impact of fast time-resolved X-ray studies. Technically, the turn-key-type femtosecond optical lasers with high peak power, used as pumps in many X-ray pump-probe experiments, have only recently become available.

The elastic properties of compressed Fe and FeO are examined using density of states measured by nuclear resonant inelastic X-ray scattering. We analyze the data both from non-hydrostatic and nearly hydrostatic experiments. The effects of preferred orientation in non-hydrostatic experiments could be substantial. We present also evidence in favor of strong softening of the Debye sound velocity due to the magnetoelastic coupling in iron oxide near the Nèel transition. The geophysical implications resulting from the elastic and magnetoelastic properties of these and related materials under compression are discussed. [ABSTRACT FROM AUTHOR]

Thermoelectrics are promising by directly generating electricity from waste heat. However, (sub-)room-temperature thermoelectrics have been a long-standing challenge due to vanishing electronic entropy at low temperatures. Topological materials offer a new avenue for energy harvesting applications. Recent theories predicted that topological semimetals at the quantum limit can lead to a large, non-saturating thermopower and a quantized thermoelectric Hall conductivity approaching a universal value. Here, we experimentally demonstrate the non-saturating thermopower and quantized thermoelectric Hall effect in the topological Weyl semimetal (WSM) tantalum phosphide (TaP). An ultrahigh longitudinal thermopower S x x ~ 1.1 × 1 0 3 μ V K − 1 and giant power factor ~ 525 μ W cm − 1 K − 2 are observed at ~40 K, which is largely attributed to the quantized thermoelectric Hall effect. Our work highlights the unique quantized thermoelectric Hall effect realized in a WSM toward low-temperature energy harvesting applications. Theories predict a large thermopower and a quantized thermoelectric Hall conductivity in topological semimetals. Here, the authors observe an ultrahigh longitudinal thermopower and a giant power factor attributed to the quantized thermoelectric Hall effect in a Weyl semimetal TaP. [ABSTRACT FROM AUTHOR]

Highlights the workshop on inelastic x-ray scattering, held on May 4-6, 2004 at Argonne National Laboratory in Chicago, Illinois. Purpose of the workshop; Keynote speakers; Topics discussed.

The active site of [NiFe] hydrogenase is an excellent catalyst for hydrogen conversion with an intriguing ability to recover from exposure to dioxygen. In their Communication on page 724 ff., W. Lubitz, S. P. Cramer, and co‐workers use the synchrotron technique of nuclear resonance vibrational spectroscopy to identify normal modes associated with active‐site FeCN and FeCO motion. [ABSTRACT FROM AUTHOR]

Das aktive Zentrum der [NiFe] ‐ Hydrogenase ist ein exzellenter Katalysator der Wasserstoffumsetzung mit der faszinierenden Fähigkeit, sich nach Sauerstoffexposition zurückzubilden. W. Lubitz, S. P. Cramer et al. nutzen in ihrer Zuschrift auf S. 752 ff. die Synchrotrontechnik der kernresonanten inelastischen Streuung, um Normalmoden der Fe ‐ CN ‐ und Fe ‐ CO ‐ Bewegung im aktiven Zentrum zu identifizieren. [ABSTRACT FROM AUTHOR]