Abstract: Elucidating the binding mode of carboxylate-containing ligands to gold nanoparticles (AuNPs) is crucial to understand their stabilizing role. A detailed picture of the three-dimensional structure and coordination modes of citrate, acetate, succinate and glutarate to AuNPs is obtained by C-13 and Na-23 solid-state NMR in combination with computational modelling and electron microscopy. The binding between the carboxylates and the AuNP surface is found to occur in three different modes. These three modes are simultaneously present at low citrate to gold ratios, while a monocarboxylate monodentate (1 kappa O-1) mode is favoured at high citrate: gold ratios. The surface AuNP atoms are found to be predominantly in the zero oxidation state after citrate coordination, although trace amounts of Au delta+ are observed. Na-23 NMR experiments show that Na+ ions are present near the gold surface, indicating that carboxylate binding occurs as a 2e(-) L-type interaction for each oxygen atom involved. This approach has broad potential to probe the binding of a variety of ligands to metal nanoparticles.

Abstract: X-ray absorption studies of the geometric and electronic structure of primarily heterogeneous Co, Ni, and Mn based water oxidation catalysts are reviewed. The X-ray absorption near edge and extended X-ray absorption fine structure studies of the metal K-edge, characterize the metal oxidation state, metal-oxygen bond distance, metal-metal distance, and degree of disorder of the catalysts. These properties guide the coordination environment of the transition metal oxide radical that localizes surface holes and is required to oxidize water. The catalysts are investigated both as-prepared, in their native state, and under reaction conditions, while transition metal oxide radicals are generated. The findings of many experiments are summarized in tables. The advantages of future X-ray experiments on water oxidation catalysts, which include the limited data available of the oxygen K-edge, metal L-edge, and resonant inelastic X-ray scattering, are discussed.

Abstract: Free borylenes (R-B:) have only been spectroscopically characterized in the gas phase or in matrices at very low temperatures However, in recent years, a few mono- and bis(Lewis base)-stabilized borylenes have been isolated In both of these compounds the boron atom is in the formal oxidation state +1 which contrasts with classical organoboron derivatives wherein the element is in the +3 oxidation state Mono(Lewis base)-stabilized borylenes are isoelectronic with singlet carbenes, and their reactivity mimics to some extent that of transition metals They can activate small molecules, such as H2, and coordinate an additional ligand; in other words, they are boron metallomimics Bis(Lewis base)borylene adducts are isoelectronic with amines and phosphines In contrast to boranes, which act as electron acceptors and thus Lewis acids, they are electron-rich and act as L ligands for transition metals This mini-review highlights significant developments in this emerging field of chemistry

Abstract: Phosphorene is emerging as an important two-dimensional semiconductor, but controlling the surface chemistry of phosphorene remains a significant challenge. Here, we show that controlled oxidation of phosphorene determines the composition and spatial distribution of the resulting oxide. We used X-ray photoemission spectroscopy to measure the binding energy shifts that accompany oxidation. We interpreted these spectra by calculating the binding energy shift for 24 likely bonding configurations, including phosphorus oxides and hydroxides located on the basal surface or edges of flakes. After brief exposure to high-purity oxygen or high-purity water vapor at room temperature, we observed phosphorus in the +1 and +2 oxidation states; longer exposures led to a large population of phosphorus in the +3 oxidation state. To provide insight into the spatial distribution of the oxide, transmission electron microscopy was performed at several stages during the oxidation. We found crucial differences between oxygen an...

Abstract: We demonstrate herein that Mn3+ and not Mn2+, as commonly accepted, is the dominant dissolved manganese cation in LiPF6-based electrolyte solutions of Li-ion batteries with lithium manganate spinel positive and graphite negative electrodes chemistry. The Mn3+ fractions in solution, derived from a combined analysis of electron paramagnetic resonance and inductively coupled plasma spectroscopy data, are ∼80% for either fully discharged (3.0 V hold) or fully charged (4.2 V hold) cells, and ∼60% for galvanostatically cycled cells. These findings agree with the average oxidation state of dissolved Mn ions determined from X-ray absorption near-edge spectroscopy data, as verified through a speciation diagram analysis. We also show that the fractions of Mn3+ in the aprotic nonaqueous electrolyte solution are constant over the duration of our experiments and that disproportionation of Mn3+ occurs at a very slow rate.

Abstract: A meta-terphenyl unit was substituted with an isocyanide group on each of its two terminal aryls to afford a bidentate chelating ligand (CNtBuAr3NC) that is able to stabilize chromium in its zerovalent oxidation state. The homoleptic Cr(CNtBuAr3NC)3 complex luminesces in solution at room temperature, and its excited-state lifetime (2.2 ns in deaerated THF at 20 °C) is nearly 2 orders of magnitude longer than the current record lifetime for isoelectronic Fe(II) complexes, which are of significant interest as earth-abundant sensitizers in dye-sensitized solar cells. Due to its chelating ligands, Cr(CNtBuAr3NC)3 is more robust than Cr(0) complexes with carbonyl or monodentate isocyanides, manifesting in comparatively slow photodegradation. In the presence of excess anthracene in solution, efficient energy transfer and subsequent triplet–triplet annihilation upconversion is observed. With an excited-state oxidation potential of −2.43 V vs Fc+/Fc, the Cr(0) complex is a very strong photoreductant. The findings...

Abstract: Perovskites have attracted attention in recent years as an economic alternative to noble metals in oxidation processes. Synthesis conditions of LaCoO3 and LaMnO3 perovskites have been studied varying citrate to nitrate molar ratio in the starting solution, pH and calcination protocol, with the aim of obtaining high purity perovskites, absence of impurities, and with enhanced textural properties. Once synthesis conditions were established, strontium was incorporated in the perovskite lattice as a textural and structural promoter, by substituting lanthanum with different doping levels, i.e. La0.9Sr0.1BO3, La0.8Sr0.2BO3, La0.7Sr0.3BO3, La0.6Sr0.4BO3 and La0.5Sr0.5BO3 with B = Co or Mn. The prepared solids were characterized in terms of crystalline phase identification (XRD), specific surface area (N2 adsorption–desorption at −196 °C), reducibility and oxidation state of transition metal ions (H2-TPR), quantification of adsorbed oxygen species (O2-TPD) and surface elemental composition (XPS). Charge imbalance associated to strontium (Sr2+) incorporation in the perovskite lattice in substitution of lanthanum (La3+) was preferentially balanced by Mn4+ promotion in La1−xSrxMnO3 perovskites, whereas formation of oxygen vacancies seems to be the mechanism for charge compensation in La1−xSrxCoO3 perovskites, where Co ions remained as Co3+ ions. Strontium doped perovskites further improved NO conversion compared to the non-substituted formulations. The best NO oxidation performance was obtained with La0.7Sr0.3CoO3 and La0.9Sr0.1MnO3 samples, achieving maximum NO conversion of 83 and 65% at 300 and 325 °C, respectively. Higher oxidation capacity of La0.7Sr0.3CoO3 sample was associated to the higher oxygen mobility and exchange capacity between oxygen in the lattice and gas phase oxygen. It is worth noting that prepared perovskites presented far higher NO oxidation capacity than platinum-based NSR model catalysts, confirming perovskites as an economic alternative to catalyze NO oxidation reactions in automotive catalysis.

Abstract: Over 70 years of chemical investigations have shown that plutonium exhibits some of the most complicated chemistry in the periodic table. Six Pu oxidation states have been unambiguously confirmed (0 and +3 to +7), and four different oxidation states can exist simultaneously in solution. We report a new formal oxidation state for plutonium, namely Pu2+ in [K(2.2.2-cryptand)][PuIICp″3], Cp″ = C5H3(SiMe3)2. The synthetic precursor PuIIICp″3 is also reported, comprising the first structural characterization of a Pu–C bond. Absorption spectroscopy and DFT calculations indicate that the Pu2+ ion has predominantly a 5f6 electron configuration with some 6d mixing.

Abstract: For the first time, we suggest VO1.52(OH)0.77 and Al-doped VO1.52(OH)0.77 as possible candidate electrode materials for aqueous zinc-ion batteries (ZIBs). Structural analysis data indicate successful doping of Al into the hollandite VO1.52(OH)0.77 tunnel structure, as confirmed by Rietveld refinement of the X-ray diffraction data (XRD) and X-ray absorption near edge structure (XANES) spectroscopy data. Al is preferred to replace V3+, such that the resulting average oxidation state of V increases with increasing Al content in V1−xAlxO1.52(OH)0.77. Electrochemical test results indicate significant improvement in capacity and retention in the Al-doped V1−xAlxO1.52(OH)0.77 due to the presence of strong Al–O bonds, which stabilizes the crystal structure. This is confirmed from the post-cycled data that show less variation in the lattice parameters. Combining the XRD and XANES data, we suggest that the present V1−xAlxO1.52(OH)0.77 is activated by the V4+/3+ redox reaction, accompanied by Zn2+ insertion into the tunnel structure upon reduction and Zn2+ extraction upon oxidation.

Abstract: Across the periodic table the trans-influence operates, whereby tightly bonded ligands selectively lengthen mutually trans metal–ligand bonds. Conversely, in high oxidation state actinide complexes the inverse-trans-influence operates, where normally cis strongly donating ligands instead reside trans and actually reinforce each other. However, because the inverse-trans-influence is restricted to high-valent actinyls and a few uranium(V/VI) complexes, it has had limited scope in an area with few unifying rules. Here we report tetravalent cerium, uranium and thorium bis(carbene) complexes with trans C=M=C cores where experimental and theoretical data suggest the presence of an inverse-trans-influence. Studies of hypothetical praseodymium(IV) and terbium(IV) analogues suggest the inverse-trans-influence may extend to these ions but it also diminishes significantly as the 4f orbitals are populated. This work suggests that the inverse-trans-influence may occur beyond high oxidation state 5f metals and hence could encompass mid-range oxidation state actinides and lanthanides. Thus, the inverse-trans-influence might be a more general f-block principle. The inverse-trans-influence has been shown to operate in high oxidation state actinide complexes. Here, the authors report tetravalent cerium, uranium and thorium bis(carbene) complexes with trans C=M=C cores where experimental and theoretical data also suggest the presence of an inverse-trans-effect.

Abstract: This article highlights recent advances in the development of transition metal-based catalysts for formaldehyde oxidation, particularly the enhancement of their catalytic activity for low-temperature oxidation. Various factors that enhance low-temperature activity are reviewed, such as morphology and tunnel structures, synthesis methods, specific surface area, amount and type of active surface oxygen species, oxidation state, and density of active sites are discussed. In addition, catalyst immobilization for practical air purification, reaction mechanism of formaldehyde oxidation, and the reaction parameters affecting the overall efficiency of the reaction are also reviewed.

Abstract: Terminal iron nitrides (Fe≡N) have been proposed as intermediates of (bio)catalytic nitrogen fixation, yet experimental evidence to support this hypothesis has been lacking. In particular, no prior synthetic examples of terminal Fe≡N species have been derived from N2. Here we show that a nitrogen-fixing Fe–N2 catalyst can be protonated to form a neutral Fe(NNH2) hydrazido(2−) intermediate, which, upon further protonation, heterolytically cleaves the N–N bond to release [FeIV≡N]+ and NH3. These observations provide direct evidence for the viability of a Chatt-type (distal) mechanism for Fe-mediated N2-to-NH3 conversion. The physical oxidation state range of the Fe complexes in this transformation is buffered by covalency with the ligand, a feature of possible relevance to catalyst design in synthetic and natural systems that facilitate multiproton/multielectron redox processes.

Abstract: Single-atom catalysts have attracted much interest recently because of their excellent stability, high catalytic activity, and remarkable atom efficiency. Inspired by the recent experimental discovery of a highly efficient single-atom catalyst Pd1/γ-Al2O3, we conducted a comprehensive DFT study on geometries, stabilities and CO oxidation catalytic activities of M1/γ-Al2O3 (M=Pd, Fe, Co, and Ni) by using slab-model. One of the most important results here is that Ni1/Al2O3 catalyst exhibits higher activity in CO oxidation than Pd1/Al2O3. The CO oxidation occurs through the Mars van Krevelen mechanism, the rate-determining step of which is the generation of CO2 from CO through abstraction of surface oxygen. The projected density of states (PDOS) of 2p orbitals of the surface O, the structure of CO-adsorbed surface, charge polarization of CO and charge transfer from CO to surface are important factors for these catalysts. Although the binding energies of Fe and Co with Al2O3 are very large, those of Pd and Ni are small, indicating that the neighboring O atom is not strongly bound to Pd and Ni, which leads to an enhancement of the reactivity of the O atom toward CO. The metal oxidation state is suggested to be one of the crucial factors for the observed catalytic activity.

Abstract: The role of molecular oxygen dissolved in the solvent is often discussed as being an influential factor on particle oxidation during pulsed laser ablation in liquids. However, the formation of the particles during laser synthesis takes place under extreme conditions that enable the decomposition of the liquid medium. Reactive species of the solvent may then affect particle formation due to a chemical reaction in the reactive plasma. Experimental results show a difference between the role of dissolved molecular oxygen and the contribution from the oxygen in water molecules. Using a metallic Cu target in air-saturated water, laser ablation led to 20.5 wt % Cu, 11.5 wt % Cu2 O, and 68 wt % CuO nanoparticles, according to X-ray diffraction results. In contrast to particles obtained in air-saturated water, no CuO was observed in the colloid synthesized in a Schlenk ablation chamber in completely oxygen-free water. Under these conditions, less-oxidized nanoparticles (25 wt % Cu and 75 wt % Cu2 O) were synthesized. The results show that nanoparticle oxidation during laser synthesis is mainly caused by reactive oxygen species from the decomposition of water molecules. However, the addition of molecular oxygen promotes particle oxidation. Storage of the Cu colloid in the presence of dissolved oxygen leads, due to aging, to nanostructures with a higher oxidation state than the freshly prepared colloid. The XRD pattern of the sample prepared in air-saturated acetone showed no crystalline phases, which is possibly due to small crystallites or low particle concentration. Concentration of the particles by centrifugation showed that in the large fraction (>20 nm), even less oxidized nanoparticles (46 wt % Cu and 54 wt % Cu2 O) were present, although the solubility of molecular oxygen is higher in acetone than in water. The nanoparticles in acetone were stable due to a Cu-catalyzed graphite layer formed on their surfaces. The influence of the solvent on alloy synthesis is also crucial. Laser ablation of PtCu3 in air-saturated water led to separated large CuO and Pt-rich spherical nanoparticles, whereas homogeneous PtCu3 alloy nanoparticles were formed in acetone.

Abstract: A pair of coordination polymers of composition (NBu4)2[M2(fan)3] (fan = fluoranilate; M = Fe and Zn) were synthesized and structurally characterized. In each case the compound consists of a pair of interpenetrating three-dimensional, (10,3)-a networks in which metal centers are linked by chelating/bridging fluoranilate ligands. Tetrabutylammonium cations are located in the spaces between the two networks. Despite the structural similarity, significant differences exist between (NBu4)2[Fe2(fan)3] and (NBu4)2[Zn2(fan)3] with respect to the oxidation states of the metal centers and ligands. For (NBu4)2[Fe2(fan)3] the structure determination as well as Mossbauer spectroscopy indicate the oxidation state for the Fe is close to +3, which contrasts with the +2 state for the Zn analogue. The differences between the two compounds extends to the ligands, with the Zn network involving only fluoranilate dianions, whereas the average oxidation state for the fluoranilate in the Fe network lies somewhere between −2 and ...

Abstract: The geometric constraints imposed by a tetradentate P4N2 ligand play an essential role in stabilizing square planar Fe complexes with changes in metal oxidation state. The square pyramidal Fe0(N2)(P4N2) complex catalyzes the conversion of N2 to N(SiR3)3 (R = Me, Et) at room temperature, representing the highest turnover number of any Fe-based N2 silylation catalyst to date (up to 65 equiv N(SiMe3)3 per Fe center). Elevated N2 pressures (>1 atm) have a dramatic effect on catalysis, increasing N2 solubility and the thermodynamic N2 binding affinity at Fe0(N2)(P4N2). A combination of high-pressure electrochemistry and variable-temperature UV–vis spectroscopy were used to obtain thermodynamic measurements of N2 binding. In addition, X-ray crystallography, 57Fe Mossbauer spectroscopy, and EPR spectroscopy were used to fully characterize these new compounds. Analysis of Fe0, FeI, and FeII complexes reveals that the free energy of N2 binding across three oxidation states spans more than 37 kcal mol–1.

Abstract: Charge transfer is a general phenomenon observed for all endohedral mono-metallofullerenes Since the detection of the first endohedral metallofullerene (EMF), La@C82, in 1991, it has always been observed that the oxidation state of a given encapsulated metal is always the same, regardless of the cage size No crystallographic data exist for any early actinide endohedrals and little is known about the oxidation states for the few compounds that have been reported Here we report the X-ray structures of three uranium metallofullerenes, U@D3h-C74, U@C2(5)-C82 and U@C2v(9)-C82, and provide theoretical evidence for cage isomer dependent charge transfer states for U Results from DFT calculations show that U@D3h-C74 and U@C2(5)-C82 have tetravalent electronic configurations corresponding to U4+@D3h-C744- and U4+@C2(5)-C824- Surprisingly, the isomeric U@C2v(9)-C82 has a trivalent electronic configuration corresponding to U3+@C2v(9)-C823- These are the first X-ray crystallographic structures of uranium EMFs and this is first observation of metal oxidation state dependence on carbon cage isomerism for mono-EMFs

Abstract: A series of novel CrOx-ZrO2 mixed oxide catalysts are prepared via a sol-gel method. Within a range of Cr/Zr atomic ratios, the mixed oxides maintain high surface area, homogeneous amorphous phases. As compared to CrOx-only catalysts formed using the same method, the addition of zirconia greatly enhances the catalytic performance for ambient-temperature, low-concentration NO oxidation. X-ray Photoelectron Spectroscopy (XPS) and Electron Paramagnetic Resonance (EPR) analyses indicate an electronic effect of ZrO2 addition to the oxidation state of Cr. That is, ZrO2 addition induces an increase in surface concentrations of Cr6+. Rapid deactivation of a pre-reduced catalyst, coupled with the fact that a deactivated catalyst contains lower concentrations of surface Cr6+, provide rather strong evidence for a Mars-van Krevelen NO oxidation mechanism. Such a mechanism is also consistent with in situ DRIFTS observations.

Abstract: Herein, we report the synthesis of a non-precious metal dual-doped catalyst. Melamine and lipoic acid were used as precursors for the nitrogen and sulfur dopant atoms, respectively, which were mixed with iron precursors and carbon black and pyrolyzed at 700 °C to yield the catalyst Fe-M-LA/C. Fe-M-LA/C shows high oxygen reduction reaction (ORR) capability, with an almost-ideal electron transfer number of 3.99. It shows almost no degradation after potential cycling for 30 000 cycles, and the structural analysis indicates that a graphene-like structure of Fe-M-LA/C can improve its ORR activity, electrical conductivity, and corrosion resistance. X-ray photoelectron spectroscopy (XPS) results show that the catalyst has high contents of pyridinic- and quaternary N atoms and thiophene S atoms that can significantly enhance the ORR performance of Fe-M-LA/C. X-ray absorption spectroscopy (XAS) data show that the oxidation state of iron and the interatomic distance of the heteroatoms in Fe-M-LA/C play an important role in determining the ORR ability. These data confirm that the presence of a nitrogen and sulfur dual-doped –Fe–N–S– structure can enhance the ORR kinetics.

Abstract: P2-type manganese-based oxide materials have received attention as promising cathode materials for sodium ion batteries because of their low cost and high capacity, but their reaction and failure mechanisms are not yet fully understood. In this study, the reaction and failure mechanisms of β-Na0.7[Mn1–xLix]O2+y (x = 0.02, 0.04, 0.07, and 0.25), α-Na0.7MnO2+y, and β-Na0.7MnO2+z are compared to clarify the dominant factors influencing their electrochemical performances. Using a quenching process with various amounts of a Li dopant, the Mn oxidation state in β-Na0.7[Mn1–xLix]O2+y is carefully controlled without the inclusion of impurities. Through various in situ and ex situ analyses including X-ray diffraction, X-ray absorption near-edge structure spectroscopy, and inductively coupled plasma mass spectrometry, we clarify the dependence of (i) reaction mechanisms on disordered Li distribution in the Mn layer, (ii) reversible capacities on the initial Mn oxidation state, (iii) redox potentials on the Jahn–Tel...

Abstract: Mixed oxidation states of manganese oxides are widely used as the electrodes in supercapacitors due to their high theoretical pseudocapacitances. However, their charge storage mechanisms are not yet fully understood. In this work, the charge storage mechanism of Mn3O4 or Mn2+(Mn3+)2O4 nanofibres was investigated using a synchrotron-based X-ray absorption spectroscopy (XAS) technique and an in situ electrochemical quartz crystal microbalance (EQCM). The average oxidation state of the Mn in the as-synthesized Mn3O4 is +2.67. After the first charge, the average oxidation states of Mn at the positive and negative electrodes are +2.61 and +2.38, respectively. The significant change in the oxidation state of Mn at the negative electrode is due to phase transformation of Mn3O4 to NaδMnOx·nH2O. Meanwhile, the charge storage mechanism at the positive electrode mainly involves the adsorption of counter ions or solvated SO42−. After the first discharge, the calculated Mn average oxidation numbers are +2.51 and +2.53 at the positive and negative electrodes, respectively. At the negative electrode, the solvated Na+ is desorbed from the electrode surface. At the same time, the solvated SO42− is desorbed from the positive electrode. The mass change of solvated Na+ during charging/discharging is ca. 80 ng per cm2 of the Mn3O4 electrode. A symmetric supercapacitor constructed from Mn3O4 nanofibres in 0.5 M Na2SO4 provides a working potential of 1.8 V, a specific energy of 37.4 W h kg−1 and a maximum specific power of 11.1 kW kg−1 with 98% capacity retention over 4500 cycles. The understanding of the charge storage mechanism of the mixed oxidation states of Mn2+(Mn3+)2O4 presented in this work could lead to further development of metal oxide-based pseudocapacitors.

Abstract: The role of trivalent rare-earth dopants on the cerium oxidation state has been systematically studied by in situ photoemission spectroscopy with synchrotron radiation for 10 mol % rare-earth doped epitaxial ceria films. It was found that dopant rare-earths with smaller ionic radius foster the formation of Ce3+ by releasing the stress strength induced by the cation substitution. With a decrease of the dopant ionic radius from La3+ to Yb3+, the out-of-plane axis parameter of the crystal lattice decreases without introducing macroscopic defects. The high crystal quality of our films allowed us to comparatively study both the ionic conductivity and surface reactivity ruling out the influence of structural defects. The measured increase in the activation energy of films and their enhanced surface reactivity can be explained in terms of the dopant ionic radius effects on the Ce4+ → Ce3+ reduction as a result of lattice relaxation. Such findings open new perspectives in designing ceria-based materials with tail...