Abstract: Ni–Fe and Ni–Fe–Co mixed-metal oxide (MMO) films were investigated as electrocatalysts for the oxygen evolution reaction (OER) in 0.1 M KOH. In an effort to optimize MMO morphology, aniline was used as a capping agent to produce high-surface-area Ni–Fe–Co films on Raney nickel supports. This catalyst exhibits enhanced mass activity in comparison to the Ni–Fe OER electrocatalysts reported to date. Cyclic voltammetry shows changes in the potential of the Ni2+/3+ transitions in Fe- or Co-containing MMO films. In situ X-ray absorption spectroscopy (XAS) analysis confirms that Fe acts to stabilize Ni in the 2+ oxidation state, while Co facilitates oxidation to the 3+ state. The results of this study support the recent claims that Fe (not Ni) is the OER active site. The OER enhancement of the ternary Ni–Fe–Co catalyst results from two effects: (1) the charge-transfer effects of Co result in the formation of the conductive NiIIIOOH phase at lower overpotential, thus activating the Fe sites which are otherwise in...

Abstract: Surface-directed corner-sharing MnO6 octahedra within numerous manganese oxide compounds containing Mn3+ or Mn4+ oxidation states show strikingly different catalytic activities for water oxidation, paradoxically poorest for Mn4+ oxides, regardless of oxidation assay (photochemical and electrochemical). This is demonstrated herein by comparing crystalline oxides consisting of Mn3+ (manganite, γ-MnOOH; bixbyite, Mn2O3), Mn4+ (pyrolusite, β-MnO2) and multiple monophasic mixed-valence manganese oxides. Like all Mn4+ oxides, pure β-MnO2 has no detectable catalytic activity, while γ-MnOOH (tetragonally distorted Mn3+O6, D4h symmetry) is significantly more active and Mn2O3 (trigonal antiprismatic Mn3+O6, D3d symmetry) is the most active. γ-MnOOH deactivates during catalytic turnover simultaneous with the disappearance of crystallographically defined corner-sharing Mn3+O6 and the appearance of Mn4+. In a comparison of 2D-layered crystalline birnessites (δ-MnO2), the monovalent Mn4+ form is catalytically inert, wh...

Abstract: The relationship between oxidation state, structure, and magnetism in many molecules is well described by first-order Jahn–Teller distortions. This relationship is not yet well defined for ligated nanoclusters and nanoparticles, especially the nano-technologically relevant gold-thiolate protected metal clusters. Here we interrogate the relationships between structure, magnetism, and oxidation state for the three stable oxidation states, −1, 0 and +1 of the thiolate protected nanocluster Au25(SR)18. We present the single crystal X-ray structures of the previously undetermined charge state Au25(SR)18+1, as well as a higher quality single crystal structure of the neutral compound Au25(SR)180. Structural data combined with SQUID magnetometry and DFT theory enable a complete description of the optical and magnetic properties of Au25(SR)18 in the three oxidation states. In aggregate the data suggests a first-order Jahn–Teller distortion in this compound. The high quality single crystal X-ray structure enables an analysis of the ligand–ligand and ligand–cluster packing interactions that underlie single-crystal formation in thiolate protected metal clusters.

Abstract: Manganese substituted cobalt ferrites, i.e., Co1−xMnxFe2O4 (0.0 ≤ x ≤ 0.4) were prepared by a solid state reaction method. XRD analysis confirmed the formation of a single-phase cubic spinel structure for all of the synthesized compositions, whereas an SEM study revealed that Mn substitution changes the microstructure. 57Fe Mossbauer spectroscopy measurements suggested that Fe3+ cations progressively migrate with Mn addition from tetrahedral (A) sites to octahedral (B) sites which have a relatively smaller covalency. Therefore, the distribution of cations between the A- and B-sites changed with increasing x. Moreover, interestingly, the Fe2+/Fe3+ cation ratio remains zero and high spin Fe3+ is the only oxidation state observed at both sites for all of the synthesized compositions. In order to explore the effects of observed variations in the microstructure and cation distribution on the dielectric and resistive properties, the prepared samples were subjected to impedance spectroscopic experiments in a wide frequency range at room temperature. Mn substitution is found to improve the resistive properties by about two orders of magnitude. This increase in the resistive properties is explained in terms of the variations in the microstructure and decrease in the mobility of the charge carriers associated with the cations redistribution. Similarly, the variation in the dielectric permittivity is also conferred in terms of the change in microstructure and cation redistribution.

Abstract: To reduce energy losses in water electrolysers a fundamental understanding of the water oxidation reaction steps is necessary to design efficient oxygen evolution catalysts. Here we present CoOx/Ti electrocatalytic films deposited by thermal and plasma enhanced chemical vapor deposition (CVD) onto titanium substrates. We report electrochemical (EC), photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) measurements. The electrochemical behavior of the samples was correlated with the chemical and electronic structure by recording XPS spectra before and after each electrochemical treatment (conditioning and cyclovoltammetry). The results show that the electrochemical behavior of CoOx/Ti strongly depends on the resulting electronic structure and composition. The thermal deposition leads to the formation of a pure Co(II)Ox which transforms to a mixed Co(II)Co(III)Ox during the OER. This change in oxidation state is coupled with a decrease in overpotential from η = 0.57 V to η = 0.43 V at 5 mA cm−2. Plasma deposition in oxygen leads to a Co(III)-dominated mixed CoOx, that has a lower onset potential as deposited due to a higher Co(III) content in the initial deposited material. After the OER XPS results of the CoOx/Ti indicate a partial formation of hydroxides and oxyhydroxides on the oxide surface. Finally the plasma deposition in air, results in a CoOxOH2 surface, that is able to completely oxidizes during OER to an oxyhydroxide Co(III)OOH. With the in situ formed CoOOH we present a highly active catalyst for the OER (η = 0.34 at 5 mA cm−2; η = 0.37 V at 10 mA cm−2).

Abstract: The negative oxidation state of gold (Au) has drawn a great attention due to its unusual valence state that induces exotic properties in its compounds, including ferroelectricity and electronic polarization. Although monatomic anionic gold (Au–) has been reported, a higher negative oxidation state of Au has not been observed yet. Here we propose that high pressure becomes a controllable method for preparing high negative oxidation state of Au through its reaction with lithium. First-principles calculations in combination with swarm structural searches disclosed chemical reactions between Au and Li at high pressure, where stable Li-rich aurides with unexpected stoichiometries (e.g., Li4Au and Li5Au) emerge. These compounds exhibit intriguing structural features like Au-centered polyhedrons and a graphene-like Li sublattice, where each Au gains more than one electron donated by Li and acts as a 6p-element. The high negative oxidation state of Au has also been achieved through its reactions with other alkali...

Abstract: Abstract Oxidation state (OS) is defined using ionic approximation of bonds. Two principal algorithms are outlined for OS determination in a chemical compound described by a Lewis formula or bond graph. Typical origins of ambiguous OS values are pointed out, and the relationship between OS and the dn electron configuration of transition metals is commented on.

Abstract: We report comparable levels of covalency in cerium– and uranium–carbon multiple bonds in the iso-structural carbene complexes [M(BIPMTMS)(ODipp)2] [M = Ce (1), U (2), Th (3); BIPMTMS = C(PPh2NSiMe3)2; Dipp = C6H3-2,6-iPr2] whereas for M = Th the MC bond interaction is much more ionic. On the basis of single crystal X-ray diffraction, NMR, IR, EPR, and XANES spectroscopies, and SQUID magnetometry complexes 1–3 are confirmed formally as bona fide metal(IV) complexes. In order to avoid the deficiencies of orbital-based theoretical analysis approaches we probed the bonding of 1–3via analysis of RASSCF- and CASSCF-derived densities that explicitly treats the orbital energy near-degeneracy and overlap contributions to covalency. For these complexes similar levels of covalency are found for cerium(IV) and uranium(IV), whereas thorium(IV) is found to be more ionic, and this trend is independently found in all computational methods employed. The computationally determined trends in covalency of these systems of Ce ∼ U > Th are also reproduced in experimental exchange reactions of 1–3 with MCl4 salts where 1 and 2 do not exchange with ThCl4, but 3 does exchange with MCl4 (M = Ce, U) and 1 and 2 react with UCl4 and CeCl4, respectively, to establish equilibria. This study therefore provides complementary theoretical and experimental evidence that contrasts to the accepted description that generally lanthanide–ligand bonding in non-zero oxidation state complexes is overwhelmingly ionic but that of uranium is more covalent.

Abstract: The hydrogenolysis of titanium–nitrogen bonds in a series of bis(cyclopentadienyl) titanium amides, hydrazides and imides by proton coupled electron transfer (PCET) is described. Twelve different N–H bond dissociation free energies (BDFEs) among the various nitrogen-containing ligands were measured or calculated, and effects of metal oxidation state and N-ligand substituent were determined. Two metal hydride complexes, (η5-C5Me5)(py-Ph)Rh–H (py-Ph = 2-pyridylphenyl, [Rh]-H) and (η5-C5R5)(CO)3Cr−H ([Cr]R-H, R= H, Me) were evaluated for formal H atom transfer reactivity and were selected due to their relatively weak M–H bond strengths yet ability to activate and cleave molecular hydrogen. Despite comparable M–H BDFEs, disparate reactivity between the two compounds was observed and was traced to the vastly different acidities of the M–H bonds and overall redox potentials of the molecules. With [Rh]–H, catalytic syntheses of ammonia, silylamine and N,N-dimethylhydrazine have been accomplished from the corresp...

Abstract: The different oxidation states of chromium allow its bulk oxide form to be reducible, facilitating the oxygen vacancy formation process, which is a key property in applications such as catalysis. Similar to other useful oxides such as TiO2, and CeO2, the effect of substitutional metal dopants in bulk Cr2O3 and its effect on the electronic structure and oxygen vacancy formation are of interest, particularly in enhancing the latter. In this paper, density functional theory (DFT) calculations with a Hubbard + U correction (DFT+U) applied to the Cr 3d and O 2p states, are carried out on pure and metal-doped bulk Cr2O3 to examine the effect of doping on the electronic and geometric structure. The role of dopants in enhancing the reducibility of Cr2O3 is examined to promote oxygen vacancy formation. The dopants are Mg, Cu, Ni, and Zn, which have a formal +2 oxidation state in their bulk oxides. Given this difference in host and dopant oxidation states, we show that to predict the correct ground state two metal ...

Abstract: The chemistry of lanthanides (Ln=La-Lu) is dominated by the low-valent +3 or +2 oxidation state because of the chemical inertness of the valence 4f electrons. The highest known oxidation state of the whole lanthanide series is +4 for Ce, Pr, Nd, Tb, and Dy. We report the formation of the lanthanide oxide species PrO4 and PrO2 (+) complexes in the gas phase and in a solid noble-gas matrix. Combined infrared spectroscopic and advanced quantum chemistry studies show that these species have the unprecedented Pr(V) oxidation state, thus demonstrating that the pentavalent state is viable for lanthanide elements in a suitable coordination environment.

Abstract: We report measurements of the oxidation state of Fe nanoparticles within lunar soils that experienced varied degrees of space weathering. We measured >100 particles from immature, submature, and mature lunar samples using electron energy-loss spectroscopy (EELS) coupled to an aberration-corrected transmission electron microscope. The EELS measurements show that the nanoparticles are composed of a mixture of Fe0, Fe2+, and Fe3+ oxidation states, and exhibit a trend of increasing oxidation state with higher maturity. We hypothesize that the oxidation is driven by the diffusion of O atoms to the surface of the Fe nanoparticles from the oxygen-rich matrix that surrounds them. The oxidation state of Fe in the nanoparticles has an effect on modeled reflectance properties of lunar soil. These results are relevant to remote sensing data for the Moon and to the remote determination of relative soil maturities for various regions of the lunar surface.

Abstract: We developed a new technique for mitigating catalyst deactivation caused by SO2 in exhaust gases. A series of 0.1 wt %-Pt/TiO2 catalysts with different surface, crystal, and pore structures were prepared and tested for CO oxidation activity in the presence of SO2 and H2O. The order of the CO oxidation activity under the influence of SO2 was much different from that in the absence of SO2. Catalysts with a high ratio of larger pores exhibited higher catalytic activity under the influence of SO2 and H2O in the temperature range of 250–300 °C, whereas other parameters, such as BET surface area and crystal structure of the TiO2 support, had minor effects on the CO oxidation activity. The oxidation state of Pt differed significantly depending on the kind of TiO2 support. Some catalysts were less active without H2 reduction pretreatment due to the presence of oxidized Pt species.

Abstract: The properties of Ni/Co/Co-Ni/MgAl 2 O 4 catalysts in the steam reforming of acetone (SRA) were investigated regarding the metallic composition and nature of catalytic site. The catalysts were characterized by nitrogen physisorption, X-ray diffraction, X-ray absorption spectroscopy, transmission electron microscopy, and temperature programmed reduction and desorption of acetone. Experimental data revealed that the acetone conversion pathway on the Co, Co-Ni, or Ni catalysts was strongly dependent on the nature of the metal, reaction temperature, and the oxidation state of the metal atoms in nanoparticles surface atoms. Reaction data indicated that the acetone decomposition on reduced metal catalysts at high temperatures (>350 °C) occurred mainly via the H C and C CO bonds cleavage, leading to the formation of CO, H 2 , and C on the metal surface. At low temperatures (200 °C) and in the presence of H 2 in the reactor feed, the Ni catalyst catalyzed the hydrogenation of the CO and CH x species formed from acetone activation on the metallic sites, producing CH 4 . For Co-containing catalysts, at low temperatures (200–350 °C) the metal nanoparticles surface was in a higher oxidation degree and promoted the oxidation of acetone. At high temperatures (>350 °C), the hydrogenation of CH x and CO species to CH 4 was determined by the nanoparticle oxidation degree, which decreased in the order Ni > Co-Ni > Co. With increased temperature, the CH x species decomposed to C and H 2 , instead of being hydrogenated to CH 4 . The oxidation of C by H 2 O was favored on Co-containing catalysts. The reaction pathways are discussed based on theoretical data obtained from the literature.

Abstract: In all heme proteins for which crystal struc- tures are available, the NE of a histidyl residue is bonded to the heme iron and Nb is hydrogen bonded to a carbonyl oxygen of the peptide backbone. We investigate here the possibility that a change in oxidation state of the iron or a change in the ge- ometry of this hydrogen bond might change the hydrogen bond strength in a functionally significant way. Dimerization ener- gies obtained from ab initio molecular orbital calculations on the hydrogen-bonded dimer of imidazole and planar formamide are used to represent the strength of this hydrogen bond in heme proteins. The effect of a change in iron oxidation state is mod- eled by varying the positive charge on imidazole. The effect of a change in hydrogen bond geometry is studied by employing x-ray coordinates for reduced and oxidized cytochrome c, deoxy- and metmyoglobin, and deoxy- and methemoglobin. Our con- clusions are that the strength of this hydrogen bond in heme proteins is sensitive to both the oxidation state of the iron atom and to geometry changes on the order of those obtained from the x-ray coordinates. We speculate that the changes in oxida- tion state may be functionalfy coupled with changes in hydrogen bond geometry and that this hydrogen bond represents a feasi- ble pathway to link protein conformation with redox potential or reactivity of the iron atom. Imidazole rings of histidyl residues are bound to the metal in a large number of metalloproteins (1). In those proteins for which high resolution x-ray crystal structural data are available, the metal-bound imidazole rings are invariably found to be hydrogen bonded to electronegative groups on the apoprotein (2-4). The possibility that this hydrogen bond might link the tertiary structure of the protein with the reactivity of the metal has been recognized by several investigators, particularly in the case of heme proteins (5-12) in which the electronegative group is a backbone carbonyl oxygen.

Abstract: Carbon supported γ-Fe2O3 nanoparticle (γ-Fe2O3/C) possessing both superparamagnetism and activating molecular oxygen properties were prepared by an ammonia-assisted precipitation method. It could catalyze the selective oxidation of various benzyl alcohols with air as oxidant source, and could be easily recycled with an external magnet separation. The correlation between the intrinsic properties of γ-Fe2O3 nanoparticles and the catalytic performance was investigated with a series of characterizations. It shows that the oxidation state of γ-Fe2O3 nanoparticles were facile to be changed, which should be related to its inverse spinel type crystal structure with vacant cation sites. These γ-Fe2O3 nanoparticles should be the active sites and responsible for the high activity of γ-Fe2O3/C in the air oxidation of alcohols. The formation of γ-Fe2O3 nanoparticle was controlled by precipitation agent and carbon support. Using ammonia ethanol solution as precipitation agent, the hydrolysis rate of iron species could be decreased. The surface functional groups of carbon support could act as chelating sites for iron species, controlling the nucleation and growth of the γ-Fe2O3 nanoparticles in the preparation process. Dr. Xiang Wang gratefully acknowledges the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division for themore » support of this work.« less

Abstract: The oxidation/reduction behaviours of lattice oxygen and transition metals in a Li-rich manganese-based layered oxide Li[Li0.25Ni0.20Mn0.55]O1.93 are investigated by using hard X-ray photoelectron spectroscopy (HAX-PES). By making use of its deeper probing depth rather than in-house XPS analyses, we clearly confirm the formation of O− ions as bulk oxygen species in the active material. They are formed on the 1st charging process as a charge compensation mechanism for delithiation and decrease on discharging. In particular, the cation–anion dual charge compensation involving Ni and O ions is suggested during the voltage slope region of the charging process. The Ni ions in the material are considered to increase the capacity delivered by a reversible anion redox reaction with the suppression of O2 gas release. On the other hand, we found structural deterioration in the cycled material. The O− species are still observed but are electrochemically inactive during the 5th charge–discharge cycle. Also, the oxidation state of Ni ions is divalent and inactive, although that of Mn ions changes reversibly. We believe that this is associated with the structural rearrangement occurring after the activation process during the 1st charging, leading to the formation of spinel- or rocksalt-like domains over the sub-surface region of the particles.

Abstract: One-electron oxidation of organoboron L2PhB: 1 (L = oxazol-2-ylidene) afforded a dicationic diborane(6) species [L2PhB–BPhL2]·2X (X = OTf, BF4, AlCl4) 3, representing a new strategy to construct a B(sp3)–B(sp3) covalent bond. Each boron atom in 3 is in the formal oxidation state +II, and tetracoordinate with a Ph group and two oxazol-2-ylidenes. The cyclic voltammetry of 3 shows irreversible reduction and oxidation. Indeed, two-electron reduction of 3 with potassium graphite (KC8) afforded 1, making a fully reversible 1 ↔ 3 redox system, whereas two-electron oxidation with AuCl produced a boronium [L2PhBCl]OTf 4. Moreover, the reactions of 3 with isonitrile derivatives RNC: under heating conditions gave a cyano-substituted boronium [L2PhBCN]BF4 5 and a 2-boranyl-indole derivative 6, depending on the substituent R. The proposed reaction mechanism involves a borinylium radical 1•+ which is generated via a homolytic cleavage of the B–B bond of 3.

Abstract: The development of economical heterogeneous catalysts for the activation of methane is a major challenge for the chemical industry. Screening potential candidates becomes more feasible using rational catalyst design to understand the activity of potential catalysts for CH 4 activation. The focus of the present paper is the use of density functional theory to examine and elucidate the properties of doped CeO 2 . We dope with Cu and Zn transition metals having variable oxidation state (Cu), and a single oxidation state (Zn), and study the activation of methane. Zn is a divalent dopant and Cu can have a +1 or +2 oxidation state. Both Cu and Zn dopants have an oxidation state of +2 after incorporation into the CeO 2 (111) surface; however a Hubbard +U correction (+U = 7) on the Cu 3d states is required to maintain this oxidation state when the surface interacts with adsorbed species. Dissociation of methane is found to occur locally at the dopant cations, and is thermodynamically and kinetically more favorable on Zn-doped CeO 2 than Cu-doped CeO 2 . The origins of this lie with the Zn(II) dopant moving towards a square pyramidal geometry in the sub surface layer which facilitates the formation of two-coordinated surface oxygen atoms, that are more beneficial for methane activation on a reducible oxide surface. These findings can aid in rational experimental catalyst design for further exploration in methane activation processes.

Abstract: The charge and spin-state evolution of manganese and cobalt in the LaMn1–xCoxO3 (x = 0.00, 0.25, 0.50, 0.75, and 1.00) perovskite nanoparticles have been studied with soft X-ray absorption spectroscopy. The results show a gradual increase in the average oxidation state of both Mn and Co ions with cobalt doping. The average valence of the LaMn1–xCoxO3 samples remains close to 3.0, with the Mn valence increasing from 3.1 to 4.0 and the Co valence increasing from 2.0 to 3.0. The symmetry of Mn and Co was determined using multiplet calculations. Calculating the intensity-area of the oxygen K pre-edge feature confirmed an increase in covalency with increasing Mn and Co oxidation state. The ground-state composition of Mn3+ in LaMnO3, and Co3+ in LaCoO3, was investigated, and it was found that Mn3+ (D4h) and Co3+ (Oh) are mainly in their low-spin state, with 10–20% admixture of high-spin state contributions into a mixed spin ground state.

Abstract: APbI3 alkali lead iodides were prepared from aqueous (A= Na, Cs, ammonium NH4+, and methyl­ammonium CH3NH3+) and acetone (A= Li, K) solutions by a self-organization low temperature process. Diffraction analysis revealed that the methylammonium-containing system (MAPbI3) crystallizes into a tetragonal perovskite structure, whereas the alkali and NH4+ systems adopt orthorhombic structures. Morphological inspection confirmed the influence of the cation on the growth mechanism: for A = Cs and NH4+, needle-like crystallites with lengths up to 3–4 mm; for A = K, thin stripes with lengths up to 5–6 mm; and for A = MA+, dodecahedral crystallites were observed. For A = Li and Na, the APbI3 systems typically resulted in polycrystalline aggregates. Optical absorption measurements demonstrated large energy band gaps for the alkali and ammonium systems with values between 2.19 and 2.40 eV. For electronic and chemical characterization by photoelectron spectroscopy, the as-prepared powders were dissolved in di-methylformamide and re-crystallized as thin films on F:SnO2 substrates by spin-coating. The binding energy differences between Pb4f and I3d core levels are highly similar in the investigated systems and close to the value measured for PbI2, indicating similar relative partial charges and formal oxidation states. The binding energies of the alkali ions are in accordance with oxidation state +1. The X-ray excited valence band spectra of the investigated APbI3 systems exhibited similar line shapes in the region between the valence band maximum and 4.5 eV higher binding energy due to common PbI6 octahedra which dominate the electronic structure. While the ionization energy values are quite similar (6.15 ± 0.25 eV), the Fermi-level positions of the unintentionally doped materials vary for different cations and different batches of the same material, which indicates that the position of the Fermi level can be influenced by changing the process parameters.

Abstract: Gold in the +III oxidation state (AuIII) has been proposed as a promising species to mediate challenging chemical reactions. However, it is difficult to characterize the chemistry of individual AuIII species in condensed-phase systems mainly due to the interference from the AuI counterpart. Herein, by doping Au atoms into gas-phase vanadium oxide clusters, we demonstrate that the AuIII cation in the AuV2O6+ cluster is active for activation and transformation of methane, the most stable alkane molecule, into formaldehyde under mild conditions. In contrast, the AuV2O6+ cluster isomers with the AuI cation can only absorb CH4. The clusters were generated by laser ablation and mass selected to react with CH4, CD4, or CH2D2 in an ion trap reactor. The reactivity was characterized by mass spectrometry and quantum chemistry calculations. The structures of the reactant and product ions were identified by using collision-induced and 425 nm photo-induced dissociation techniques.

Abstract: We study the water oxidation mechanism of the cobalt aqua complex [Co(H2O)6]2+ in a photocatalytic setup by means of density functional theory. Assuming a water-nucleophilic-attack or radical coupling mechanism, we investigate how the oxidation state and spin configuration change during the catalytic cycle. In addition, different ligand environments are employed by substituting a water ligand with a halide, pyridine, or derivative thereof. This allows exploration of the effect of such ligands on the frontier orbitals and the thermodynamics of the water oxidation process. Moreover, the thermodynamically most promising water oxidation catalyst can be identified by comparing the computed free energy profiles to the one of an “ideal catalyst”. Examination of such simple (hypothetical) water oxidation catalysts provides a basis for the derivation of design guidelines, which are highly sought for the development of efficient homogeneous water oxidation catalysts.

Abstract: Laser ablation generated RhAl3O4+ heteronuclear metal oxide cluster cations have been mass-selected using a quadrupole mass filter and reacted with CH4 or CD4 in a linear ion trap reactor under thermal collision conditions. The reactions have been characterized by state-of-the-art mass spectrometry and quantum chemistry calculations. The RhAl3O4+ cluster can activate four C–H bonds of a methane molecule and convert methane to syngas, an important intermediate product in methane conversion to value-added chemicals. The Rh atom is the active site for activation of the C–H bonds of methane. The high electron-withdrawing capability of Rh atom is the driving force to promote the conversion of methane to syngas. The polarity of Rh oxidation state is changed from positive to negative after the reaction. This study has provided the first example of methane conversion to syngas by heteronuclear metal oxide clusters under thermal collision conditions. Furthermore, the molecular level origin has been revealed for th...

Abstract: The addition of Lewis or Bronsted acids (LA = Zn(OTf)2, B(C6F5)3, HBArF, TFA) to the high-valent manganese–oxo complex MnV(O)(TBP8Cz) results in the stabilization of a valence tautomer MnIV(O-LA)(TBP8Cz•+). The ZnII and B(C6F5)3 complexes were characterized by manganese K-edge X-ray absorption spectroscopy (XAS). The position of the edge energies and the intensities of the pre-edge (1s to 3d) peaks confirm that the Mn ion is in the +4 oxidation state. Fitting of the extended X-ray absorption fine structure (EXAFS) region reveals 4 N/O ligands at Mn–Nave = 1.89 A and a fifth N/O ligand at 1.61 A, corresponding to the terminal oxo ligand. This Mn–O bond length is elongated compared to the MnV(O) starting material (Mn–O = 1.55 A). The reactivity of MnIV(O-LA)(TBP8Cz•+) toward C–H substrates was examined, and it was found that H• abstraction from C–H bonds occurs in a 1:1 stoichiometry, giving a MnIV complex and the dehydrogenated organic product. The rates of C–H cleavage are accelerated for the MnIV(O-LA)(T...