Abstract: The present study illustrates the importance of the oxidation state of iron within the mesoporous iron trimesate [{Fe3O(H2O)2F0.81(OH)0.19}{C6H3(CO2)3}2] denoted MIL-100(Fe) (MIL= Material from Institut Lavoisier) during adsorption of molecules that can interact with the accessible metal sites through π-back donation. Adsorption of CO has been first followed by FTIR spectroscopy to quantify the Lewis acid sites in the dehydrated Fe(III) sample, outgassed at 150 °C, and on the partially reduced Fe(II/III), outgassed at 250 °C. The exposure of MIL-100(Fe) to CO2, propane, propene and propyne has then been studied by FTIR spectroscopy and microcalorimetry. It appears that π-back donating molecules are strongly adsorbed on reduced iron(II) sites despite the weaker Lewis acidity of cus Fe2+ sites compared to that of Fe3+ ones, as shown by pyridine adsorption.

Abstract: This contribution is both a review of different aspects of X-ray photoelectron spectroscopy that can help one determine U oxidation states and a personal perspective on how to effectively model the X-ray photoelectron spectroscopy of complicated mixed-valence U phases. After a discussion of the valence band, the focus lingers on the U4f region, where the use of binding energies, satellite structures, and peak shapes is discussed in some detail. Binding energies were shown to be very dependent on composition/structure and consequently unreliable guides to oxidation state, particularly where assignment of composition is difficult. Likewise, the spin orbit split 4f7/2 and 4f5/2 peak shapes do not carry significant information on oxidation states. In contrast, both satellite-primary peak binding energy separations, as well as intensities to a lesser extent, are relatively insensitive to composition/structure within the oxide–hydroxide–hydrate system and can be used to both identify and help quantify U oxidation states in mixed valence phases. An example of the usefulness of the satellite structure in constraining the interpretation of a complex multivalence U compound is given. Copyright © 2011 John Wiley & Sons, Ltd.

Abstract: The chemistry of the s-block metals is dominated by the +1 oxidation state for the Alkali metals (group 1) and the +2 oxidation state for the Alkaline Earth metals (group 2). In recent years, a series of stable dimeric magnesium(I) compounds has been prepared and their chemistry has started to develop. These complexes feature “deformable” Mg–Mg single bonds and are stabilised by sterically demanding and chelating anionic N-ligands that prevent their disproportionation. They have rapidly proven useful in organic and organometallic/inorganic reduction reactions as hydrocarbon soluble, stoichiometric, selective and safe reducing agents. The scope of this perspective focuses on stable molecular compounds of the general type LMgMgL and describes their synthesis, structures, theoretical and spectroscopic studies as well as their further chemistry. Also, comparisons are drawn with related complexes including magnesium(II) hydrides and dimeric zinc(I) compounds.

Abstract: Ligand noninnocence occurs for complexes composed of redox-active ligands and metals, with frontier orbitals of similar energy. Usually methods of analysis can be used to define the charge distribution, and cases where the metal oxidation state and ligand charge are unclear are unusual. Ligands derived from o-benzoquinones can bond with metals as radical semiquinonates (SQ•–) or as catecholates (Cat2–). Spectroscopic, magnetic, and structural properties can be used to assess the metal and ligand charges. With the redox activity at both the metal and ligands, reversible multicomponent redox series can be observed using electrochemical methods. Steps in the series may occur at either the ligand or metal, and ligand substituent effects can be used to tune the range of ligand-based redox steps. Complexes that appear as intermediates in a ligand-based redox series may contain both SQ and Cat ligands “bridged” by the metal as mixed-valence complexes. Properties reflect the strength of metal-mediated interligand...

Abstract: Various transition metal (TM) doped zinc oxide nanoparticles with the composition TMxZn1−xO (TM = V, Mn, Fe, Co, and Ni; x = 0.01−0.3) were prepared by a microwave-assisted nonaqueous sol−gel route in benzyl alcohol within a few minutes. The high doping levels in the range 20−30 atom % achieved for Co and Fe provide a promising opportunity to study the magnetic properties of such potential diluted magnetic semiconductors. However, only Fe0.2Zn0.8O was ferromagnetic at room temperature. The Co-doped sample showed Curie−Weiss behavior up to a doping level of 30 atom %. According to X-ray absorption fine structure (XAFS) measurements, at high doping levels the Fe-doped ZnO samples contain an increasing fraction of Fe3+ ions (in addition to Fe2+), whereas Co is predominantly in the oxidation state of +2. Clustering of Fe ions into amorphous ferromagnetic Fe3O4 within the ZnO host and the magnetic interactions between the Fe3O4 regions is a possible explanation for the ferromagnetic properties.

Abstract: New phases of Zn–Co-layered double hydroxides (Zn–Co-LDHs) were synthesized for the first time via a co-precipitation reaction using hydrogen peroxide as an oxidant. According to powder X-ray diffraction and field emission-scanning electron microscopy, both nitrate- and sulfate-forms of the Zn–Co-LDHs crystallized with the brucite-type layer structure having interlayer nitrate and sulfate anions, respectively, and commonly showed plate-like morphology with a crystal size of several hundred nanometers. dc magnetic susceptibility measurements revealed that the Zn–Co-LDHs displayed ferromagnetic/antiferromagnetic transitions below 15 K and the magnetic moment calculated from the paramagnetic region (30–300 K) indicated the co-existence of weak field Co2+ and strong field Co3+ ions. The mixed oxidation state of Co2+/Co3+ was confirmed by the results of iodometry and X-ray absorption near-edge structure spectroscopy. The heat-treatment for the Zn–Co–LDHs at elevated temperatures produced mixed metal oxide nanocomposites composed of spinel ZnCo2O4 and wurzite ZnO phases. The colloidal suspension of exfoliated Zn–Co-LDH nanosheets could be synthesized by dispersion of the pristine LDH materials in formamide, which was confirmed by the Tyndall phenomenon, high resolution-transmission electron microscopy/selected area electron diffraction, and UV-vis spectroscopy. The Zn–Co-LDH film fabricated with the restacked nanosheets exhibited pseudocapacitive behavior with a large specific capacitance and a good capacitance retention. The present findings underscore that the newly synthesized mixed valence Zn–Co-LDH phases showed promising functionality as a supercapacitor electrode material and also showed interesting magnetic coupling behavior.

Abstract: An alternative activation method was developed to stabilize the Metal Organic Framework (MOF) MIL-47(V) material in the VIII oxidation state. This solid and the oxidized forms were investigated by in situ infrared and Raman spectroscopies, X-ray diffraction (XRD), and Complex Impedance Spectroscopy (CIS). Unlike MIL-47(VIV), MIL-47(VIII) is a flexible structure which presents μ2-hydroxyl groups acting as preferential adsorption sites for H2O or CO2. The modulation of the oxidation state of the metal center of this porous material leads to new intermediate porous solids with mixed oxidation states VIII/VIV. In these materials, the VIII and VIV centers seem to occur in close vicinity. However, the presence of VIV centers inhibits the flexibility to a large extent.

Abstract: Ce–Fe mixed oxides were prepared by urea gelation coprecipitation method and used as supports of gold catalysts. The impact of the support composition on the catalytic performance for the preferential CO oxidation (PROX) was studied by varying the Ce/(Ce + Fe) ratio. A deep characterization study by different tools such as XRD, HRTEM, TPR and FTIR spectroscopy was undertaken in order to correlate the structural characteristics of the catalysts and the gold oxidation state and dispersion with the catalytic properties. The results revealed that the variation of the support composition led to significant differences in the gold particles size (in the range 1–25 nm), which affected strongly the CO oxidation activity of Au/CeO2–Fe2O3 catalysts under PROX conditions. The following activity order was observed: Au/CeO2 ≈ Au/Ce50Fe50 > Au/Ce75Fe25 > Au/Ce25Fe75 > Au/Fe2O3. The support with composition 50 wt.% CeO2–50 wt.% Fe2O3 appeared beneficial not only for nucleation and growth of highly dispersed gold particles (1–1.8 nm), but also for activation of oxygen and its mobility. Moreover, the presence of Fe2O3 in the supports composition improved the resistance towards deactivation by CO2. The CeO2–Fe2O3 supports comprised different amount of two phases: cubic CeO2-like solid solution and hematite. The analysis of the characterization data suggested that the solid solution formation probably proceeded via a dopant interstitial compensation mechanism.

Abstract: A series of monocarbonyl iron complexes in the formal oxidation states 0, +1, and +2 are accessible when supported by a tetradentate tris(phosphino)silyl ligand (SiPiPr3 = [Si(o-C6H4PiPr2)3]−). X-ray diffraction (XRD) studies of these carbonyl complexes establish little geometrical change about the iron center as a function of oxidation state. It is possible to functionalize the terminal CO ligand of the most reduced carbonyl adduct by addition of SiMe3+ to afford a well-defined iron carbyne species, (SiPiPr3)Fe≡C—OSiMe3. Single-crystal XRD data of this iron carbyne derivative reveal an unusually short Fe≡C—OSiMe3 bond distance (1.671(2) A) and a substantially elongated C−O distance (1.278(3) A), consistent with Fe−C carbyne character. The overall trigonal bipyramidal geometry of (SiPiPr3)Fe≡C—OSiMe3 compares well with that of the corresponding carbonyls, (SiPiPr3)Fe(CO)−, (SiPiPr3)Fe(CO), and (SiPiPr3)Fe(CO)+. Details regarding the electronic structure of the carbyne complex have been explored via the co...

Abstract: A method of pH manipulation has been used to improve chemically oxidative polymerization of m-phenylenediamine (mPD) through concurrent addition of NaOH when adding oxidant (NH4)2S2O8. pH detection and open-circuit potential technique were adopted to monitor the polymerization process of mPD and to explain the oxidation state–pH and yield–pH relationships. Results from Fourier transformed infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies indicate that a low oxidation state is under control by regulating NaOH concentration. At 2.5 M NaOH, the oxidation state of poly(m-phenylenediamine) (PmPD) is 64.7 mol % (measured by molar content of quinoid imine from XPS), while the yield is 84%. The synthesized PmPD possesses better Ag+ adsorption performance when lowering its oxidation state. Moreover, the Ag+ adsorbance of PmPD can reach 1693 mg g–1. Meanwhile, Ag+ adsorption mechanism was studied by pH tracking, X-ray diffraction (XRD) patterns, and X-ray photoelectron spectroscopy. The adsorption proces...

Abstract: A significant limitation in our understanding of the molecular mechanism of biological nitrogen fixation is the uncertain composition of the FeMo-cofactor (FeMo-co) of nitrogenase. In this study we present a systematic, density functional theory-based evaluation of spin-coupling schemes, iron oxidation states, ligand protonation states, and interstitial ligand composition using a wide range of experimental criteria. The employed functionals and basis sets were validated with molecular orbital information from X-ray absorption spectroscopic data of relevant iron-sulfur clusters. Independently from the employed level of theory, the electronic structure with the greatest number of antiferromagnetic interactions corresponds to the lowest energy state for a given charge and oxidation state distribution of the iron ions. The relative spin state energies of resting and oxidized FeMo-co already allowed exclusion of certain iron oxidation state distributions and interstitial ligand compositions. Geometry-optimized...

Abstract: The family of polynuclear manganese clusters of formula [Mn12O12(O2CR)16(H2O)4] (R = Et, Ph, etc.) has been investigated in great detail over the years for their ability to function as single-molec...

Abstract: The Shilov system, a mixture of di- and tetravalent chloroplatinate salts in aqueous solution, provided the first indication of the potential of organotransition metal complexes for activating and functionalizing alkanes under mild conditions; the participation of higher-valent species plays a crucial role. In this chapter, we discuss the experimental and computational studies that have led to detailed mechanistic understanding of C-H activation and functionalization by both the original Shilov system and the many subsequent modifications that have been developed, and assess the prospects for practical, selective catalytic oxidation of alkanes using this chemistry.

Abstract: We model monomeric vanadia adspecies on the CeO2(111) surface of composition VOn·Ce12O24 (n = −1, 0, ..., 4) using the DFT+U approach and statistical thermodynamics. At low oxygen pressure (10−9 atm), VO4 is the most stable species below 400 K; in the 400−900 K range, VO2 is stable; and above 900 K, VO becomes stable. In all of these systems, vanadium is stabilized in the +5 oxidation state. Using the energies of hydrogenation and oxygen vacancy formation as reactivity descriptors, we predict an enhanced reactivity of the vanadia/ceria system in Mars−van Krevelen-type oxidation reactions. At the origin of this support effect is the ability of ceria to stabilize reduced states by accommodating electrons in localized f states. We also calculate the frequencies of the normal vibrational modes of the supported VOn species and their infrared intensity.

Abstract: Atomistic simulations were carried out to characterize the coordination environments of U incorporated in three Fe-(hydr)oxide minerals: goethite, magnetite, and hematite. The simulations provided information on U−O and U−Fe distances, coordination numbers, and lattice distortion for U incorporated in different sites (e.g., unoccupied versus occupied sites, octahedral versus tetrahedral) as a function of the oxidation state of U and charge compensation mechanisms (i.e., deprotonation, vacancy formation, or reduction of Fe(III) to Fe(II)). For goethite, deprotonation of first shell hydroxyls enables substitution of U for Fe(III) with a minimal amount of lattice distortion, whereas substitution in unoccupied octahedral sites induced appreciable distortion to 7-fold coordination regardless of U oxidation states and charge compensation mechanisms. Importantly, U−Fe distances of ∼3.6 A were associated with structural incorporation of U and cannot be considered diagnostic of simple adsorption to goethite surfac...

Abstract: We have studied the electronic properties of single crystal based ceria and magnesia−ceria model catalysts, the CO2 adsorption, and the CO2-induced reoxidation of these systems by synchrotron radiation photoelectron spectroscopy (SR-PES). All model systems were prepared starting from a fully stoichiometric and well-ordered CeO2(111) film grown on Cu(111). Different magnesia−ceria mixed oxide films were prepared by physical vapor deposition (PVD) of magnesium, oxygen treatment, and subsequent annealing. The preparation procedure was varied to obtain samples with different oxidation state, structure, and surface composition. Different carbon-containing species were identified, including surface carbonates formed in the vicinity of Mg2+ and Ce3+/4+ and surface carboxylates. The presence of Mg2+ was observed to strongly enhance carbonate formation but suppress the formation of carboxylates. Changes in the oxidation state of ceria upon CO2 exposure were monitored with highest sensitivity by resonant photoelect...

Abstract: The Fe oxidation state, coordination geometry, and distances have been determined by Fe K -edge XANES and EXAFS for a set of silicate glasses of phonolite composition produced at different oxygen fugacity conditions with the aim of determining the effect of iron oxidation state and local structural environment on the viscosity of the corresponding melts. Comparison of the pre-edge peak data with those of Fe model compounds with known oxidation state and coordination number allowed for determination of the Fe oxidation state and coordination number for all the glasses analyzed. The Fe3+/(Fe3++Fe2+) ratio varies from 0.44 to 0.93 (±0.05) in the glasses studied. The determined values are in excellent agreement (within 0.03 difference) with those independently measured by the titration method. Moreover, pre-edge peak data clearly indicate that Fe3+ is in fourfold coordination, whereas Fe2+ exists both in fourfold and fivefold coordination for this phonolitic composition, although the presence of minor amounts of sixfold-coordinated Fe cannot be ruled out by XANES data alone. EXAFS data of the most oxidized sample indicate that Fe3+ is in tetrahedral coordination with = 1.85 A (±0.01). This value compares well with literature data for [4]Fe3+ (e.g., in tetra-ferriphlogopite or rodolicoite). Calculated NBO/T ratios decrease with Fe oxidation (from 0.23 to 0.19). For phonolitic glasses of this study, going from reducing to oxidizing conditions results in a higher fraction of network-forming Fe, thus increasing the polymerization of the tetrahedral network and producing shorter (and stronger) bond distances. Both the polymerization increase and the structural variations in the Fe local environment can qualitatively explain the strong increase in melt viscosity observed at higher oxygen fugacity.

Abstract: The oxidation state of vanadium in natural and synthetic Fe–Ti oxides is determined using high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS). Eleven natural magnetite-bearing samples from a borehole of the Main Magnetite Layer of the Bushveld Complex (South Africa), five synthetic Fe oxide samples, and three natural hematite-bearing samples from Dharwar supergroup (India) are investigated. V K edge spectra were recorded on the ID26 beamline at the European Synchrotron Radiation Facility (Grenoble, France), and the pre-edge features were used to determine the local environment and oxidation state of vanadium. In the case of the magnetite samples (natural and synthetic), we show that vanadium is incorporated in the octahedral site of the spinel structure under two oxidation states: +III and +IV. The variations of the pre-edge area are interpreted as various proportions in V3+ and V4+ (between 9.5 and 16.3% of V4+), V3+ being the main oxidation state. In particular, the variations of the V4+/V3+ ratio along the profile of the Main Magnetite Layer seem to follow the crystallization sequence of the layer. In the case of the hematite samples from India, the pre-edge features indicate that vanadium is substituted to Fe and mainly incorporated as V4+ (between 40 and 72% of V4+). We also demonstrate the potentiality of HERFD-XAS for mineralogical studies, since it can filter out the unwanted fluorescence and give better resolved spectra than conventional XAS.

Abstract: X-ray powder diffraction (XRPD), Infrared, Raman, and UV/Vis spectroscopy have been used to investigate the structural, vibrational, and optical properties of Ti and Mg chloride tetrahydrofuranates as precursors of heterogeneous Ziegler-Natta catalysts for polyethylene production; as well as their interaction compound (pro-catalyst) and the final catalyst obtained after interaction with the AlR(3) activator. Although the structure of the precursors and of the pro-catalyst were well known, that of the catalyst (obtained by reaction of the pro-catalyst with AlR(3)) was not easily obtainable from XRPD data. IR and Raman spectroscopy provided important information on tetrahydrofuran (thf) coordination and on the ν(M-Cl) region; whereas UV/Vis spectroscopy gave the direct proof on both the formal oxidation state and the coordination environment of the active Ti sites. Those presented herein are among the first direct experimental data on the structure of the active Ti sites in Ziegler-Natta catalysts, and can be used to validate the many computational studies that have been increasing exponentially in the last few decades.

Abstract: Electrochemical adsorption of SO2 on platinum is complicated by the change in sulfur oxidation state with potential. Here, we attempt to identify SO2 adsorption products on catalyst coated membrane...

Abstract: Layered monodiphosphate Li9V3(P2O7)3(PO4)2 can be synthesized by direct solid-state reaction using either hydrogen or carbon as the reducing agent at the sintered temperature of 750 °C When the temperature is higher than 800 °C, Li9V3(P2O7)3(PO4)2 begins to decompose into Li3V2(PO4)3 and Li4P2O7 The measurement results of electronic conductivity, magnetization, and electrochemical impedance spectroscopy are reported for the first time After carbon coating, the electronic conductivity comes to 207 × 10−3 S cm−1, which is the same order of magnitude as that of carbon-coated LiFePO4 and Li3V2(PO3)4 Li-ion diffusion coefficient (419 × 10−10 cm2 s−1) for carbon-uncoated Li9V3(P2O7)3(PO4)2 is close to that of LiCoO2 and much higher than that of LiFePO4 Li9V3(P2O7)3(PO4)2 exhibits a paramagnetic behavior in the temperature range of 5−300 K, which is consistent with the result from our X-ray photoelectron spectroscopy analysis where the oxidation state of vanadium is +3 in the Li9V3(P2O7)3(PO4)2 compound

Abstract: Platinum supported on a mixed metal oxide, NbRu{sub y}O{sub z} (8Nb:1Ru), was evaluated as an electrocatalyst for the ethanol oxidation reaction (EOR) in 0.1 M HClO{sub 4} and 1 M KOH. The support was synthesized from a liquid precursor solution of metal chlorides that was aerosolized and thermally decomposed into a powder via the spray pyrolysis (SP) process. Two samples were of primary interest: 30%Pt deposited onto the support by dry impregnation and 60%Pt as part of the precursor solution that underwent in situ SP Pt dispersion. TEM, SEM, and XRD were used to confirm morphology and deposition of Pt. XPS and XAS studies confirmed elemental distribution and oxidation state of Pt catalyst. In situ IRRAS studies in 0.1 M HClO{sub 4} show that these electrocatalysts are capable of facilitating the complete oxidation pathway of EOR, involving scission of the C-C bond and CO oxidation.