Abstract: The critical role of the Auger parameter in providing insight into both initial state and final state factors affecting measured XPS binding energies is illustrated by analysis of Ni 2p3/2 and L3M45M45 peaks as well as the Auger parameters of nickel alloys, halides, oxide, hydroxide and oxy-hydroxide. Analyses of the metal and alloys are consistent with other works, showing that final state relaxation shifts, ΔR, are determined predominantly by changes in the d electron population and are insensitive to inter-atomic charge transfer. The nickel halide Auger parameters are dominated by initial state effects, Δe, with increasing positive charge on the core nickel ion induced by increasing electronegativity of the ligands. This effect is much greater than the final state shifts; however, the degree of covalency is reflected in the Wagner plot where the more polarizable iodide and bromide have greater ΔR. The initial state shift for NiO is much smaller than those of Ni(OH)2 or NiOOH and the effective oxidation state is much less than that inferred from the average electronegativity of the ligand(s). Auger parameter analysis indicates that the bonding in NiO appears to have stronger contributions from initial state charge transfer from the oxygen ligands than that in the hydroxide and oxyhydroxide consistent with the considerable differences in the Ni–O bond lengths in these compounds with some relaxation of this state occurring during final state phenomena. The Auger parameter of NiOOH is, however, shifted positively, like the iodide, indicating greater polarizability of the ligands and covalency in this bonding. There is support for more direct use of relative bond lengths in interpreting differences between related compounds rather than more general electronegativity or similar parameters.

Abstract: Catecholates and 2-amidophenoxides are prototypical “noninnocent” ligands which can form metal complexes where the ligands are best described as being in the monoanionic (imino)semiquinone or neutral (imino)quinone oxidation state instead of their closed-shell dianionic form. Through a comprehensive analysis of structural data available for compounds with these ligands in unambiguous oxidation states (109 amidophenolates, 259 catecholates), the well-known structural changes in the ligands with oxidation state can be quantified. Using these correlations, an empirical “metrical oxidation state” (MOS) which gives a continuous measure of the apparent oxidation state of the ligand can be determined based on least-squares fitting of its C–C, C–O, and C–N bond lengths to this single parameter (a simple procedure for doing so is provided via a spreadsheet in the Supporting Information). High-valent d0 metal complexes, particularly those of vanadium(V) and molybdenum(VI), have ligands with unexpectedly positive, a...

Abstract: Arsenic (As) is an element belonging to the group V-A, and it demonstrates characteristics of a metalloid. Because arsenic more easily forms anions, its non-metal properties dominate. When arsenic is in an oxidation state of +5, it acts similar to phosphorus, a fact that has many implications for the way in which it reacts in soil, as well as its potential toxicity in plants. The most common oxidation states of As are −3, 0, +3, and +5. Arsines and metal arsines are those in which As has an oxidation state of −3, and these forms are very unstable under oxidizing conditions. Under aerobic conditions, the oxidation state of As tends to be +5, and when this occurs at a pH between 2 and 3, arsenic acid (H3AsO4) is formed. When the pH rises to values between 3 and 11, this compound disassociates to H2AsO 4 − and HAsO 4 2− (Smedley and Kinninburgh 2002). Under anaerobic conditions, the predominant As species is H3AsO3.

Abstract: Trivalent cerium ions in CeO2 are the key active species in a wide range of catalytic and electro-catalytic reactions. We employed ambient pressure X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy to quantify simultaneously the concentration of the reactive Ce3+ species on the surface and in the bulk of Sm-doped CeO2(100) in hundreds of millitorr of H2–H2O gas mixtures. Under relatively oxidizing conditions, when the bulk cerium is almost entirely in the 4+ oxidation state, the surface concentration of the reduced Ce3+ species can be over 180 times the bulk concentration. Furthermore, in stark contrast to the bulk, the surface’s 3+ oxidation state is also highly stable, with concentration almost independent of temperature and oxygen partial pressure. Our thermodynamic measurements reveal that the difference between the bulk and surface partial molar entropies plays a key role in this stabilization. The high concentration and stability of reactive surface Ce3+ over wide ranges of...

Abstract: Extensive quantum chemical DFT calculations were performed on the high-resolution (1.9 A) crystal structure of photosystem II in order to determine the protonation pattern and the oxidation states of the oxygen-evolving Mn cluster. First, our data suggest that the experimental structure is not in the S1-state. Second, a rather complete set of possible protonation patterns is studied, resulting in very few alternative protonation patterns whose relevance is discussed. Finally, we show that the experimental structure is a mixture of states containing highly reduced forms, with the largest contribution (almost 60%) from the S–3-state, Mn(II,II,III,III).(1)

Abstract: In situ spatially resolved X-ray absorption near edge structure (μ-XANES) spectra are obtained for natural Cu-In-bearing sphalerite. Copper K -edge spectral data show that, in Cu-In-bearing sphalerite, in which an excellent correlation between the Cu and In contents is noted, Cu is present in the Cu + state. This offers indirect proof for the coupled substitution 2 Zn 2+ ↔ Cu + + In 3+ , which allows indium to enter the sphalerite structure. The study clearly demonstrates the utility of synchrotron radiation to accurately determine oxidation state in small volumes of mineral in which the concentration of the element of interest is low or very low. The study also demonstrates that good quality μ-XANES spectra can be collected on TEM foils prepared in situ at a chosen position on the surface of a polished sample using the focused ion beam–scanning electron microscope method.

Abstract: The ability of Mo (Cr) impurities in a CaO (MgO) matrix to act as charge donors to adsorbed gold has been investigated by means of scanning tunneling microscopy and density functional theory. Whereas CaO(Mo) features a robust donor characteristic, as deduced from a charge-transfer-driven crossover in the Au particles' geometry in the presence of dopants, MgO(Cr) is electrically inactive. The superior performance of the CaO(Mo) system is explained by the ability of the Mo ions to evolve from a +2 oxidation state in ideal CaO to a +5 state by transferring up to three electrons to the Au adislands. Cr ions in MgO, on the other hand, are stable only in the +2 and +3 charge states and can provide a single electron at best. Since this electron is likely to be captured by cationic vacancies or morphological defects in the real oxide, no charge transfer to Au particles takes place in this case. On the basis of our findings, we have developed general rules on how to optimize the electron donor characteristics of doped oxide materials.

Abstract: We present a density-functional study of the adsorption and reactions of oxygen and water with the (100) surface of pyrite. We find that dissociative adsorption is energetically favorable for oxygen, forming ferryl-oxo, Fe(4+)═O(2-), species. These transform easily to ferric-hydroxy, Fe(3+)-OH(-), in the presence of coadsorbed water, and the latter fully covers the surface under room conditions. A mechanism for surface oxidation is identified, which involves successive reactions with molecular oxygen and water, and leads to the complete oxidation of a surface sulfur to SO4(2-). The crucial recurring process is the surface O(2-) and OH(-) species acting as proton acceptors for incoming water molecules. Using a recently proposed method, we examine the oxidation state changes of the surface ions and the electron flow during the adsorption and oxidation processes. The oxidation mechanism is consistent with isotopic labeling experiments, suggesting that the oxygens in SO4(2-) from gas-phase oxidation are derived from water.

Abstract: There are provided methods and systems for an electrochemical cell including an anode and a cathode where the anode is contacted with a metal ion that converts the metal ion from a lower oxidation state to a higher oxidation state. The metal ion in the higher oxidation state is reacted with hydrogen gas, an unsaturated hydrocarbon, and/or a saturated hydrocarbon to form products.

Abstract: TiO2-supported manganese oxide catalysts formed using different calcination temperatures were prepared by using the wet-impregnation method and were investigated for their activity in the low-temperature selective catalytic reduction (SCR) of NO by NH3 with respect to the Mn valence and lattice oxygen behavior. The surface and bulk properties of these catalysts were examined using Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and temperature-programmed desorption (TPD). Catalysts prepared using lower calcination temperatures, which contained Mn4+, displayed high SCR activity at low temperatures and possessed several acid sites and active oxygen. The TPD analysis determined that the Bronsted and Lewis acid sites in the Mn/TiO2 catalysts were important for the low-temperature SCR at 80∼160 and 200∼350 °C, respectively. In addition, the available lattice oxygen was important for attaining high NO to NO2 oxidation at low temperatures. Implications:...

Abstract: The hydrothermal stability of Fe−BEA as a selective catalytic reduction (SCR) catalyst was experimentally studied. Cordierite supported Fe−BEA samples were hydrothermally treated at 600 and 700 °C for 3−100 h to capture the effect of aging time and temperature. Before and after aging the samples were characterized with BET, XPS, XRD, and NH3-TPD. The catalytic performance of the samples with respect to NO oxidation, NH3 oxidation, and NO reduction (NH3-SCR) was studied by flow reactor experiments to correlate changes of the catalytic performance with structural changes of the zeolite and the iron phases. The NH3-SCR experiments did not show any significant decrease in activity after a short time of aging (3 h at 700 °C)even though the ammonia storage capacity decreased by 40% and the oxidation state of iron slightly increased. A longer time of aging resulted in decreased activity for NO reduction during low temperatures (150−300 °C), while at higher temperatures (400−500 °C) the activity remained high. The results indicate that the NO reduction is more sensitive at low temperatures to changes in the oxidation state of iron caused by hydrothermal aging than at higher temperatures. Furthermore, a maximum in activity for NO oxidation and increased oxidation state of iron (Fe3+) indicate Fe2O3 particle growth.

Abstract: A large series of doped cerias have been prepared by the coprecipitation method combined with impregnation and completely characterized in order to have an overall understanding of the structural, oxygen vacancy concentration, and transport properties relationships. Several lanthanides were incorporated in the fluorite structure, and the effects of the final sintering temperature (1073 and 1573 K) and the addition of cobalt oxide on the structural properties were studied. The chosen lanthanides (Gd, La, Tb, Pr, Eu, Er, Yb and Nd) included a large range of ionic radii and different metals exhibiting variable oxidation states under the typical operating conditions for these materials. The materials have been characterized by powder XRD, high-temperature XRD, micro-Raman spectroscopy, helium pycnometry, and dc conductivity. Transport properties were correlated with structural features induced by the different ionic radii and variable oxidation state of the dopants. The highest ionic conductivity was obtained...

Abstract: As part of our interest in novel redox-active main group/transition metal platforms for energy applications, we have synthesized the chloride salt of [TeIIIPtICl(o-dppp)2]+ ([1]+, o-dppp = o-(Ph2P)C6H4) by reaction of the new bis(phosphino) telluroether (o-(Ph2P)C6H4)2Te with (Et2S)2PtCl2. Complex [1]+ is chemically robust and undergoes a clean two-electron oxidation reaction in the presence of PhICl2 to afford ClTeIIIPtIIICl3(o-dppp)2 (2), a complex combining a hypervalent four-coordinate tellurium atom and an octahedral platinum center. While the Te–Pt bond length is only slightly affected by the oxidation state of the TePt platform, DFT and NBO calculations show that this central linkage undergoes an umpolung from Te→Pt in [1]+ to Te←Pt in 2. This umpolung signals an increase in the electron releasing ability of the tellurium center upon switching from an eight-electron configuration in [1]+ to a hypervalent configuration in 2. Remarkably, the two-electron redox chemistry displayed by this new dinuclea...

Abstract: The development of innovative metal catalysis for selective bond formation is an important task in organic chemistry. The group 13 metal indium is appealing for catalysis because indium-based reagents are minimally toxic, selective, and tolerant toward various functional groups. Among elements in this group, the most stable oxidation state is typically +3, but in molecules with larger group 13 atoms, the chemistry of the +1 oxidation state is also important. The use of indium(III) compounds in organic synthesis has been well-established as Lewis acid catalysts including asymmetric versions thereof. In contrast, only sporadic examples of the use of indium(I) as a stoichiometric reagent have been reported: to the best of our knowledge, our investigations represent the first synthetic method that uses a catalytic amount of indium(I).Depending on the nature of the ligand or the counteranion to which it is coordinated, indium(I) can act as both a Lewis acid and a Lewis base because it has both vacant p orbital...

Abstract: Iron oxidation state and coordination geometry have been determined by Fe K-edge X-ray absorption near edge spectroscopy (XANES) for three sets of silicate glasses of peralkaline rhyolitic composition with different peralkalinity values. These compositions were chosen to investigate the effect of alkali content (and oxygen fugacity) on the Fe oxidation state. The samples were produced by means of hydrothermal vessels at 800 °C with oxygen fugacity conditions ranging from NNO-1.61 to NNO+2.96 log units. Comparison of the pre-edge peak data with those of Fe model compounds of known oxidation state and coordination number allowed determination of the Fe oxidation state and coordination number in all glasses analyzed. Within each group of samples, Fe tends to oxidize with increasing oxygen fugacity as expected. However, alkali content is shown to have a strong effect on the Fe3+/(Fe3++Fe2+) ratio at constant oxygen fugacity: this ratio varies from 0.25 to 0.55 (±0.05) for the least peralkaline series, and from 0.45 to 0.80 (±0.05) for the most peralkaline series. Moreover, pre-edge peak data clearly indicate that Fe3+ is in fourfold coordination in the most peralkaline glasses. Extrapolation of pre-edge peak data suggests the presence of both fourfold and fivefold coordination for trivalent Fe in the other two series. Divalent Fe is suggested to be mainly in fivefold coordination in all the three glass series. The presence of minor amounts of sixfold- and fourfold-coordinated Fe cannot be ruled out by XANES data alone. XANES data suggest that the amount of alkalis also affects the Fe3+ coordination environment resulting in a decrease in the average coordination numbers. Extended X-ray absorption fine structure (EXAFS) data of the most oxidized and peralkaline sample indicate that Fe3+ is in tetrahedral coordination with = 1.85 A (±0.02). This value compares well with literature data for [4]Fe3+ in crystalline phases (e.g., in tetra-ferriphlogopite or rodolicoite) or in silicate glasses (e.g., phonolite glasses) supporting the XANES-determined coordination number obtained for the most peralkaline glasses. Calculated NBO/T ratios decrease slightly with Fe oxidation because of the higher fraction of network forming Fe, thus increasing the polymerization of the tetrahedral network.

Abstract: Protein metalation processes are crucial for the mechanism of action of several anticancer metallodrugs and warrant deeper characterisation. We have explored the reactions of three cytotoxic gold(III) compounds—namely [(bipy2Me)2Au2(μ-O)2][PF6]2 (where bipy2Me is 6,6′-dimethyl-2,2′-bipyridine) (Auoxo6), [(phen2Me)2Au2(μ-O)2][PF6]2 (where phen2Me is 2,9-dimethyl-1,10-phenanthroline) (Au2phen) and [(bipydmb-H)Au(OH)][PF6] [where bipydmb-H is deprotonated 6-(1,1-dimethylbenzyl)-2,2′-bipyridine] (Aubipyc)—with two representative model proteins, i.e. horse heart cytochrome c and hen egg white lysozyme, through UV–visible absorption spectroscopy and electrospray ionisation mass spectrometry (ESI MS) to characterise the inherent protein metalation processes. Notably, Auoxo6 and Au2phen produced stable protein adducts where one or more “naked” gold(I) ions are protein-coordinated; very characteristic is the case of cytochrome c, which upon reaction with Auoxo6 or Au2phen preferentially forms “tetragold” adducts with four protein-bound gold(I) ions. In turn, Aubipyc afforded monometalated protein adducts where the structural core of the gold(III) centre and its +3 oxidation state are conserved. Auranofin yielded protein derivatives containing the intact auranofin molecule. Additional studies were performed to assess the role played by a reducing environment in protein metalation. Overall, the approach adopted provides detailed insight into the formation of metallodrug–protein derivatives and permits trends, peculiarities and mechanistic details of the underlying processes to be highlighted. In this respect, electrospray ionisation mass spectrometry is a very straightforward and informative research tool. The protein metalation processes investigated critically depend on the nature of both the metal compound and the interacting protein and also on the solution conditions used; thus, predicting with accuracy the nature and the amounts of the adducts formed for a given metallodrug–protein pair is currently extremely difficult.

Abstract: An Au/CeO2 model catalyst was prepared by deposition–precipitation, with the aim of obtaining a sample suitable for a detailed X-ray absorption fine structure (XAFS) analysis of the gold–ceria interface structure. The results demonstrate the existence of a large interface between the gold particle and the support oxide, characterized by well-defined Au–O and Au–Ce interactions extending up to ∼6.4 A. The complex interface structure is retained after CO treatment up to 250 °C and subsequent reoxidation at 400 °C. The analysis of the XANES spectra, and the Au–O distance of 2.21 A, longer than Au–O bond lengths previously reported for Au/ceria catalysts, suggest a low oxidation state for the gold atoms placed at the interface between Au and ceria.

Abstract: Lattice oxygen of TiO2 is activated by the substitution of Pd ion in its lattice. Ti1–xPdxO2–x (x = 0.01–0.03) have been synthesized by solution combustion method crystallizing in anatase TiO2 structure. Pd is in +2 oxidation state and Ti is in +4 oxidation state in the catalyst. Pd is more ionic in TiO2 lattice compared to Pd in PdO. Oxygen storage capacity defined by “amount of oxygen that is used reversibly to oxidize CO” is as high as 5100 μmol/g of Ti0.97Pd0.03O1.97. Oxygen is extracted by CO to CO2 in absence of feed oxygen even at room temperature which is more than 20 times compared to pure TiO2. Rate of CO oxidation is 2.75 μmol g–1 s–1 at 60 °C over Ti0.97Pd0.03O1.97 and C2H2 gets oxidized to CO2 and H2O at room temperature. Catalyst is not poisoned on long time operation of the reactor. Such high catalytic activity is due to activated lattice oxygen created by the substitution of Pd ion as seen from first-principles density functional theory (DFT) calculations with 96 atom supercells of Ti32O64...