Oxo Ions Research Articles

Synthesis, Structure, and Bonding of d3 Molybdenum–Oxo Complexes

AbstractReduction of d2 metal–oxo ions of the form [MO(PP)2Cl]+ (M=Mo, W; PP=chelating diphosphine) produces d3 MO(PP)2Cl complexes, which include the first isolated examples in group 6. The stability and reactivity of the MO(PP)2Cl compounds are found to depend upon the steric bulk of the phosphine ligands: derivatives with bulky phosphines that shield the oxo ligand are stable enough to be isolated, whereas those with phosphines that leave the oxo ligand exposed are more reactive and observed transiently. Magnetic measurements and DFT calculations on MoO(dppe)2Cl indicate the d3 compounds are low spin with a 2[(dxy)2(π*(MoO))1] configuration. X‐ray crystallographic and vibrational‐spectroscopic studies on d2 and d3 [MoO(dppe)2Cl]0/+ establish that the d3 compound possesses a reduced M−O bond order and significantly longer Mo−O bond, accounting for its greater reactivity. These results indicate that the oxo‐centered reactivity of d3 complexes may be controlled through ligand variation.

Effect of the Nuclearity and Coordination of Cu and Fe Sites in β Zeolites on the Oxidation of Hydrocarbons

Cu and Fe zeolites can activate oxygen for oxidative reactions of methane and stable hydrocarbon molecules. Here, we analyzed the activity of Cu and Fe sites with various nuclearities and coordinations in *BEA zeolites toward complete oxidation of methane, toluene, and ethanol by molecular oxygen. Spectral analysis of the interaction of methane with the individual Cu and Fe sites and a kinetic study show that the oxidation of methane is catalyzed by different active sites with different activation energies. In the low-temperature region (225–325 °C), the activity is primarily caused by reactive bridging oxygen atoms in dimeric Cu and Fe clusters. Isolated Fe3+-oxo ions in the octahedral coordination and Cu2+ partially charge-balanced by the framework with less rigid redox states contribute to the activity at higher temperatures of ≥350 °C. The isolated Fe3+-oxo ions tetrahedrally coordinated to the framework oxygen and the bare Cu2+ ions charge-balanced exclusively by the framework are strongly stabilized and cannot act as active sites. Oxidation of the hydrocarbons over both the dimeric and isolated Cu and Fe active sites is nonspecific with practically barrierless consecutive reactions of already activated molecules and therefore fully CO2-selective for all of the hydrocarbons in an excess of oxygen.

Structure of a Ferryl Mimic in the Archetypal Iron(II)- and 2-(Oxo)-glutarate-Dependent Dioxygenase, TauD.

Iron(II)- and 2-(oxo)-glutarate-dependent (Fe/2OG) oxygenases catalyze a diverse array of oxidation reactions via a common iron(IV)-oxo (ferryl) intermediate. Although the intermediate has been characterized spectroscopically, its short lifetime has precluded crystallograhic characterization. In solution, the ferryl was first observed directly in the archetypal Fe/2OG hydroxylase, taurine:2OG dioxygenase (TauD). Here, we substitute the iron cofactor of TauD with the stable vanadium(IV)-oxo (vanadyl) ion to obtain crystal structures mimicking the key ferryl complex. Intriguingly, whereas the structure of the TauD·(VIV-oxo)·succinate·taurine complex exhibits the expected orientation of the V≡O bond-trans to the His255 ligand and toward the C-H bond to be cleaved, in what has been termed the in-line configuration-the TauD·(VIV-oxo) binary complex is best modeled with its oxo ligand trans to Asp101. This off-line-like configuration is similar to one recently posited as a means to avoid hydroxylation in Fe/2OG enzymes that direct other outcomes, though neither has been visualized in an Fe/2OG structure to date. Whereas an off-line (trans to the proximal His) or off-line-like (trans to the carboxylate ligand) ferryl is unlikely to be important in the hydroxylation reaction of TauD, the observation that the ferryl may deviate from an in-line orientation in the absence of the primary substrate may explain the enzyme's mysterious self-hydroxylation behavior, should the oxo ligand lie trans to His99. This finding reinforces the potential for analogous functional off-line oxo configurations in halogenases, desaturases, and/or cyclases.

An All‐Alkynyl Protected 74‐Nuclei Silver(I)–Copper(I)‐Oxo Nanocluster: Oxo‐Induced Hierarchical Bimetal Aggregation and Anisotropic Surface Ligand Orientation

The hardness of oxo ions (O2- ) means that coinage-metal (Cu, Ag, Au) clusters supported by oxo ions (O2- ) are rare. Herein, a novel μ4 -oxo supported all-alkynyl-protected silver(I)-copper(I) nanocluster [Ag74-x Cux O12 (PhC≡C)50 ] (NC-1, avg. x=37.9) is characterized. NC-1 is the highest nuclearity silver-copper heterometallic cluster and contains an unprecedented twelve interstitial μ4 -oxo ions. The oxo ions originate from the reduction of nitrate ions by NaBH4 . The oxo ions induce the hierarchical aggregation of CuI and AgI ions in the cluster, forming the unique regioselective distribution of two different metal ions. The anisotropic ligand coverage on the surface is caused by the jigsaw-puzzle-like cluster packing incorporating rare intermolecular C-H⋅⋅⋅metal agostic interactions and solvent molecules. This work not only reveals a new category of high-nuclearity coinage-metal clusters but shows the special clustering effect of oxo ions in the assembly of coinage-metal clusters.

An All‐Alkynyl Protected 74‐Nuclei Silver(I)–Copper(I)‐Oxo Nanocluster: Oxo‐Induced Hierarchical Bimetal Aggregation and Anisotropic Surface Ligand Orientation

AbstractThe hardness of oxo ions (O2−) means that coinage‐metal (Cu, Ag, Au) clusters supported by oxo ions (O2−) are rare. Herein, a novel μ4‐oxo supported all‐alkynyl‐protected silver(I)–copper(I) nanocluster [Ag74−xCuxO12(PhC≡C)50] (NC‐1, avg. x=37.9) is characterized. NC‐1 is the highest nuclearity silver–copper heterometallic cluster and contains an unprecedented twelve interstitial μ4‐oxo ions. The oxo ions originate from the reduction of nitrate ions by NaBH4. The oxo ions induce the hierarchical aggregation of CuI and AgI ions in the cluster, forming the unique regioselective distribution of two different metal ions. The anisotropic ligand coverage on the surface is caused by the jigsaw‐puzzle‐like cluster packing incorporating rare intermolecular C−H⋅⋅⋅metal agostic interactions and solvent molecules. This work not only reveals a new category of high‐nuclearity coinage‐metal clusters but shows the special clustering effect of oxo ions in the assembly of coinage‐metal clusters.

Feasibility of application of iron zeolites for high-temperature decomposition of N2O under real conditions of the technology for nitric acid production

The long-term stabilities of a group of iron zeolites with MFI, *BEA, and FER structures and similar Fe/Al ratios were evaluated to assess their performance as catalysts for N2O decomposition. Conditions relevant for the application of the catalyst at the secondary level for N2O elimination, i.e., directly after the NH3 oxidation step of the process of nitric acid production, were investigated. These conditions included reaction temperatures of up to 900°C and the presence of high concentrations of water vapour, oxygen, and NO. The focus of the study was the comparison of the MFI and *BEA zeolites with the FER-based zeolite, a catalyst established as relatively stable under such conditions. The structural analysis of the individual zeolite frameworks and iron species involved a combination of several methods, and provided insight into the framework modification as well as identification and semiquantitative determination of the individual iron species. In the zeolite catalysts, these iron species were in the form of either isolated Fe(II) and Fe(III)-oxo ions, polynuclear Fe(III)-oxo complexes, or small Fe oxide particles. None of the zeolite structures displayed a high extent of structural collapse of the framework; thus, structural collapse does not explain the observed decrease in activity. An investigation of the kinetics of the N2O decomposition, both before and after ageing under relevant reaction conditions, proved the dominant role of isolated Fe(II) ions that were accessible to the reacting gas-phase molecules. The kinetic study also identified the differences in the ability of the three zeolites to stabilize the active sites in individual framework types during long-term exposure to challenging reaction conditions. It has been shown that, while the isolated Fe(II) ions were present in adequate concentration for N2O decomposition activity at the relevant temperature region in all three zeolite-based catalysts, the MFI and *BEA zeolites were not able to effectively stabilize the active iron structure during ageing for over 12days. In contrast, the FER framework survived a test for over 24days. The iron species formed in MFI and *BEA zeolites during ageing were mostly large FeOx species and displayed very low activity that approached the activity of FeOx clusters supported on SiO2.

Experimental and Theoretical Investigation of the Anti-Ferromagnetic Coupling of CrIII Ions through Diamagnetic -O-NbV-O- Bridges.

The synthesis and properties of a novel hetero-tetranuclear compound [Cr2(bpy)4(μ-O)4Nb2(C2O4)4]·3H2O (1; bpy = 2,2'-bipyridine), investigated by single-crystal X-ray diffraction, magnetization measurements, IR, UV/visible spectroscopy, electron paramagnetic resonance (EPR; X- and Q-bands and high-field), and density functional theory (DFT) calculations, are reported. Crystal structure of 1 (orthorhombic Pcab space group) consists of a square-shaped macrocyclic {Cr2(μ-O)4Nb2} core in which CrIII and NbV ions are alternately bridged by oxo ions and three uncoordinated water molecules. The intramolecular CrIII···CrIII distances through the -O-NbV-O- bridges are 7.410(2) and 7.419(2) Å, while diagonal separation is 5.406(2) Å. The temperature dependence of magnetization M(T) evidences an anti-ferromagnetic ground state, which originates from a magnetic interaction between two CrIII ions of spin 3/2 through two triatomic -O-NbV-O- diamagnetic bridges. A spin Hamiltonian appropriate for polynuclear isolated magnetic units was used. The best-fitting curve for this model is obtained with the parameters gCr = 1.992(3), J = -12.77(5) cm-1, and |D| = 0.17(4) cm-1. The CrIII···CrIII dimer model is confirmed by EPR spectra, which exhibit a pronounced change of their shape around the temperature corresponding to the intradimer coupling J. The EPR spectra simulations and DFT calculations reveal the presence of a single-ion anisotropy that is close to being uniaxial, D = -0.31 cm-1 and E = 0.024 cm-1.

Adsorption Properties of Bentonite with In Situ Immobilized Polyaniline Towards Anionic Forms of Cr(VI), Mo(VI), W(VI), V(V)

A new composite material bentonite-PANI was synthesized by in situ immobilization of polyaniline (PANI) on the surface of natural mineral bentonite. It was established as a result of the modification of bentonite a surface area and an interlayer distance of mineral decrease and particles of bentonite transformed of irregular shape with different porosity on irregularly shaped particles of smaller size. It has been found that the total Cr(VI) ions extraction took place under the acid conditions (pH=1 – 2) and W(VI) ions have been well adsorbed in the pH range from 1 to 8 by the composite bentonite-PANI unlike the initial mineral. Whereas adsorption of oxo anions of V(V) and Mo(VI) made up some 50%. It is proved that the in situ immobilization of bentonite by polyaniline leads to increasing the value of adsorption capacity towards the investigated ions compared with the initial mineral. It was established that the adsorption properties of the synthesized composite with respect to the studied oxo ions were worse than the adsorption properties of composite vermiculite-PANI, similar to the composite Sokyryntsyy clinoptilolite-PANI and better than composites of polyaniline with Podilskyy saponite and Karelian shungite.DOI: http://dx.doi.org/10.5755/j01.ms.22.2.6976

Highly Active Gold(I)-Silver(I) Oxo Cluster Activating sp³ C-H Bonds of Methyl Ketones under Mild Conditions.

The activation of C(sp(3))-H bonds is challenging, due to their high bond dissociation energy, low proton acidity, and highly nonpolar character. Herein we report a unique gold(I)-silver(I) oxo cluster protected by hemilabile phosphine ligands [OAu3Ag3(PPhpy2)3](BF4)4 (1), which can activate C(sp(3))-H bonds under mild conditions for a broad scope of methyl ketones (RCOCH3, R = methyl, phenyl, 2-methylphenyl, 2-aminophenyl, 2-hydroxylphenyl, 2-pyridyl, 2-thiazolyl, tert-butyl, ethyl, isopropyl). Activation happens via triple deprotonation of the methyl group, leading to formation of heterometallic Au(I)-Ag(I) clusters with formula RCOCAu4Ag4(PPhpy2)4(BF4)5 (PPhpy2 = bis(2-pyridyl)phenylphosphine). Cluster 1 can be generated in situ via the reaction of [OAu3Ag(PPhpy2)3](BF4)2 with 2 equiv of AgBF4. The oxo ion and the metal centers are found to be essential in the cleavage of sp(3) C-H bonds of methyl ketones. Interestingly, cluster 1 selectively activates the C-H bonds in -CH3 rather than the N-H bonds in -NH2 or the O-H bond in -OH which is traditionally thought to be more reactive than C-H bonds. Control experiments with butanone, 3-methylbutanone, and cyclopentanone as substrates show that the auration of the C-H bond of the terminal methyl group is preferred over secondary or tertiary sp(3) C-H bonds; in other words, the C-H bond activation is influenced by steric effect. This work highlights the powerful reactivity of metal clusters toward C-H activation and sheds new light on gold(I)-mediated catalysis.

Electrochemical determination of low levels of uranyl by a vibrating gold microelectrode.

In this work we report the sensitive electroanalytical detection of uranium(VI) in aqueous solutions. Uranium commonly exists in aqueous solutions in the form of its oxo ion, uranyl (U(VI)O2(2+)). The detection of uranyl has been accomplished by us through its deposition upon reduction by two electrons to the insoluble UO2 using a bare disk gold macroelectrode and anodic stripping voltammetry (ASV). This gave an unsatisfactory detection limit of ca. 1 × 10(-5) M uranyl. Moreover, the evolution of hydrogen bubbles blocked the electrode surface as a result of water reduction at negative deposition potential (-0.7 V vs Ag/AgCl). The application of a 25 μm diameter Au microwire electrode on which UO2 precipitated at negative potential (-1.2 V) improved substantially the detection limit. Further improvement was accomplished by vibrating the microwire working electrode, which increased the amounts of UO2 deposition due to decreasing the diffusion layer. The effect of the vibrating amplitude and frequency on the electroanalytical response was studied and optimized. Eventually, a detection limit of ca. 1 × 10(-9) M uranyl was achieved using a 5 min deposition time, -1.2 V deposition potential, and vibrating the electrode at frequency of 250 Hz and amplitude of 6 V.

The Oxidation of Sulfur Dioxide by Single and Double Oxygen Transfer Paths

The oxidation of SO2 by nonmetal oxoanions in the gas phase is investigated in an experimental and theoretical study of the structure of the species involved and the reaction kinetics and mechanism. SO3 , SO3(.-) and SO4(.-) are efficiently produced by reaction of On XO(-) anions (X=Cl, Br, and I; n=0 and 1) with SO2 ; XO(-) ions mainly react to give SO3 by oxygen-atom transfer, whereas OXO(-) ions mainly give SO3(.-) by oxygen-anion transfer. On descending the halogen group from chlorine to iodine, the SO3 /SO3(.-) ratio decreases and increases for reactions involving XO(-) and OXO(-) anions, respectively, whereas the formation of SO4(.-) is particularly significant with OIO(-). Kinetic factors play a major role in the reactions of On XO(-), depending on the halogen atom and its oxidation state.

The iron(III)-modified natural zeolitic tuff as an adsorbent and carrier for selenium oxyanions

Se(IV) and Se(VI) anions are the dominant species of Se existing in aqueous systems. In this study, the iron(III)-modified natural zeolitic tuff (Fe-CLI) from the Serbian deposit Zlatokop has been investigated as an adsorbent for the Se oxyanions. Fe-CLI shows adsorption activity for both Se(IV) and Se(VI) which decreases with increasing pH. The adsorption capacity of Fe-CLI is found to be higher for Se(IV) than for Se(VI). Kinetics data follow the pseudo-second-order model and the obtained parameters k indicate that the rates of adsorption and desorption are higher for Se(VI). Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) analyses reveal that Se is bound at the zeolite surface forming not only the Se–O–Fe but also Se–O–Si bonds. The adsorption mechanism depends of the type of oxo ions. Samples of zeolitic tuff which contain Se were tested as soil supplements for the cultivation of Pleurotus ostreatus mushrooms. The fungus adsorbed the inorganic Se from zeolitic tuff transforming it to a more valuable organically bound form.

Geminal Tetraauration of Acetonitrile: Hemilabile-Phosphine-Stabilized Au8Ag4 Cluster Compounds

Unprecedented geminal tetraauration of acetonitrile has been realized through C-H activation by Au(I)-Ag(I) clusters under mild conditions. The reaction of [OAu3Ag(dppy)3](BF4)2 (dppy = diphenylphosphino-2-pyridine) (1), AgBF4, and acetonitrile in the presence of methanol at room temperature resulted in the isolation of the novel cluster [(CCN)2Au8Ag4(dppy)8(CH3CN)2](BF4)6 (2). The centrosymmetric structure consists of two Au4Ag2 motifs stabilized by hemilabile phosphines. Triply deprotonated acetonitrile (CCN(3-)) is found in a Au4Ag environment with the terminal carbon bridging four Au(I) centers and the nitrogen donor linking a Ag(I) ion, which is the first example of a μ5-CCN(3-) coordination mode. A concerted metalation/deprotonation process for the C-H activation of acetonitrile that indicates the importance of the oxo ion of the oxonium Au(I) cluster is proposed. Cluster 2 emits bright green light in the solid state at room temperature upon UV irradiation.

Synthesis, crystal structure, and spectroscopic characterization of two new binuclear complexes of manganese(II) and vanadium(V) with dipicolinate ligands containing 2-aminopyrimidinium as a counter cation

Two new binuclear complexes, formulated as [(Hamp)[Mn(μ-dipic)Cl(H2O)2]]2 and [(Hamp)[V(μ-O)(O)(dipic)]·H2O]2 (dipicH2 = pyridine-2,6-dicarboxylic (dipicolinic) acid; amp = 2-aminopyrimidine), were synthesized by a hydrothermal process and characterized by elemental analysis, IR spectroscopy, thermal analysis, and X-ray single crystal diffraction. Both compounds contain two Hamp cations and a dinuclear manganese(II) or vanadium(V) anion complex. In addition, the vanadium complex contains two lattice water molecules. Two manganese(II) ions are bridged by pyridine-2,6-dicarboxylate ions in the manganese complex, and they are both coordinated by O,N,O of the tridentate dipicolinate ligand, one oxygen of another dipicolinate ligand, one chlorine, and two water molecules in a distorted pentagonal-bipyramidal geometry. Vanadium(V) ions are coordinated octahedrally by O,N,O of the tridentate dipicolinate ligand, one oxo ion, and two bridging μ-O ions in cis position in the vanadium complex. The crystal structures of both complexes are stabilized by a complex network of hydrogen bonds comprising water molecules, counter ion, and carboxyl groups of dipic2−.

Syntheses, structures and magnetic properties of dinuclear oxo-bridged iron(III) complexes

The reaction of tris(2-pyridylmethyl)amine (TPyA)/N,N-bis(2-pyridylmethyl)-2-aminoethanol (bpaeOH), H2DHBN/Na2C2O4/NaN3 and Fe(II/III) ions in MeOH leads to the isolation of three iron(III) dimeric complexes, namely [(TPyA)(DHBN)FeIIIOFeIII(TPyA)(DHBN)]·2H2O (1), [(bpaeOH)(C2O4)FeIIIOFeIII(C2O4)(bpaeOH)]·2H2O (2) and [(TPyA)(N3)FeIIIOFeIII(N3)(TPyA)](ClO4)2 (3) (H2DHBN=3,4-dihydroxybenzonitrile). These complexes have been investigated by single crystal X-ray diffractometry and magnetochemistry. Complexes 1–3 show dimeric structures with a bridging oxo (O2−) ion, and all the iron(III) ions have a distorted octahedral geometry. Complexes 1 and 3 have offset face-to-face π–π interactions between the dimers and possess a supramolecular structure, while 2 has O–H···O hydrogen bonding interactions between the dimers, which gives rise to a 1-D chain structure. These (μ-oxo)diiron(III) complexes exhibit antiferromagnetic interactions [1: g=2.0, J/kB=−112K (−78cm−1), θ=−0.29K, ρ=0.035; 2: g=2.0, J/kB=−141K (−98cm−1), θ=−0.3K, ρ=0.01; 3: g=2.0, J/kB=−130K (−90cm−1), θ=−0.5K, ρ=0.009]. These indicate that very strong antiferromagnetic interactions occur via the oxo bridge within the iron(III) dimer and weak antiferromagnetic interactions exist between the dimers.

Two New Neptunyl(V) Selenites: A Novel Cation–Cation Interaction Framework in (NpO2)3(OH)(SeO3)(H2O)2·H2O and a Uranophane-Type Sheet in Na(NpO2)(SeO3)(H2O)

Dark green crystals of (NpO(2))(3)(OH)(SeO(3))(H(2)O)(2)·H(2)O (1) have been prepared by a hydrothermal reaction of neptunyl(V) and Na(2)SeO(4) in an aqueous solution at 150 °C, while green plates of Na(NpO(2))(SeO(3))(H(2)O) (2) have been synthesized by evaporation of a solution of neptunyl(V), H(2)SeO(4), and NaOH at room temperature. Both compounds have been characterized by single-crystal X-ray diffraction. The structure of compound contains three crystallographically unique Np atoms that are bonded to two O atoms to form a nearly linear O═Np═O NpO(2)(+) cation. Neighboring Np(5+) ions connect to each other through a bridging oxo ion from the neptunyl unit, a configuration known as cation-cation interactions (CCIs), to build a complex three-dimensional network. More specifically, each Np(1)O(2)(+), Np(2)O(2)(+), and Np(3)O(2)(+) cation is involved in three, five, and four CCIs with other units, respectively. The framework of neptunyl(V) pentagonal bipyramids is decorated by selenite trigonal pyramids with one-dimensional open channels where uncoordinated waters are trapped via hydrogen bonding interactions. Compound adopts uranophane-type [(NpO(2))(SeO(3))](-) layers, which are separated by Na(+) cations and water molecules. Within each layer, neptunyl(V) pentagonal bipyramids share equatorial edges with each other to form a single chain that is further connected by both monodentate and bidentate selenite trigonal pyramids. Crystallographic data: compound, monoclinic, P2(1)/c, Z = 4, a = 6.6363(8) Å, b = 15.440(2) Å, c = 11.583(1) Å, β = 103.549(1)°, V = 1153.8(2) Å(3), R(F) = 0.0387 for I > 2σ(I); compound (2), monoclinic, C2/m, Z = 4, a = 14.874(4) Å, b = 7.271(2) Å, c = 6.758(2) Å, β = 112.005(4)°, V = 677.7(3) Å(3), R(F) = 0.0477 for I > 2σ(I).

Production and isolation of ligated metal(IV)‐oxo ions by tandem mass spectrometry

High valent metal(IV)-oxo species, [M(==O)(MeIm)(n)(OAc)](+) (M = Mn-Ni, MeIm = 1-methylimidazole, n = 1-2), which are relevant to biology and oxidative catalysis, were produced and isolated in gas-phase reactions of the metal(II) precursor ions [M(MeIm)(n)(OAc)](+) (M = Mn-Zn, n = 1-3) with ozone. The precursor ions [M(MeIm)(OAc)](+) and [M(MeIm)(2)(OAc)](+) were generated via collision-induced dissociation of the corresponding [M(MeIm)(3)(OAc)](+) ion. The dependence of ozone reactivity on metal and coordination number is discussed.

Hydroxylation of TiO2-B: insights from density functional calculations

Density functional calculations are carried out to investigate the interaction of water with the low-index stoichiometric surfaces of the TiO2-B polymorph of titanium dioxide. Dissociative adsorption is predicted for the (100) surface, whereas mixed dissociative/molecular adsorption is favored on both the (010) and (110) surfaces. On the (001) surface, water is able to stabilize the type-II termination, which is metastable in a dry environment, by converting the oxo ions into hydroxyls. At high temperature, water desorption is likely to convert the hydroxylated type-II surface to a type-I termination, whereas the reverse type-I → type-II transition is not allowed when re-adsorption occurs. This could explain the experimental observation that surface hydroxyls on TiO2-B surfaces are not fully regenerated upon successive heating and cooling cycles.

Influence of the local atomic structure in the X-ray absorption near edge spectroscopy of neptunium oxo ions

Experimental L(III) X-ray absorption near edge structure (XANES) spectra of the distorted octahedral neptunium oxo ions NpO(2)(OH)(4)(2-), NpO(4)(OH)(2)(3-), and NpO(6)(6-) are interpreted using relativistic full multiple scattering calculations of the X-ray absorption process. In this series of compounds, the neptunium cation exhibits two different oxidation states, VI and VII, with coordination spheres from di- to tetra oxo for the first two compounds. The comparison between calculated XANES spectra using the feff code and experimental ones shows that the main features in the spectra are determined by the local coordination around the actinide metal center. Furthermore, the projected density of electronic states (DOS) calculated from the XANES simulations using the feff code are compared to calculations using ADF code. They are both discussed in terms of molecular orbitals and qualitative evolution of bonding within this series of compounds.

Adsorption properties of oxidized gallium-modified zeolite ZSM-5 from diffuse-reflectance IR-spectroscopic and quantum-chemical data: II. Interaction with carbon monoxide and water

Diffuse-reflectance IR spectroscopy was used to study the adsorption and subsequent high-temperature transformations of water and carbon monoxide molecules on the oxidation-treated gallium-modified zeolite Ga/HZSM-5. The results were correlated with the corresponding quantum-chemical calculation data. Usually, it is thought that the oxo ions [Ga=O]+ are formed in the oxidation of Ga/HZSM-5. Based on the experimental and calculated data, the possible reactions of the gallium oxo ions with the above molecules are considered. The oxo ions were found highly reactive, and it is likely that polynuclear gallium oxide nanoclusters were formed in the oxidation of the gallium-substituted zeolite Ga/HZSM-5. The Ga+ ions, which appeared in the course of Ga/HZSM-5 reduction, were partially oxidized by water at 573 K; in turn, this could initiate the formation of polynuclear nanoclusters. It was found that ∼25% of the Ga+ ions were oxidized in the interaction with water to liberate molecular hydrogen. The thermal reduction of a nitrous oxide-preoxidized Ga/HZSM-5 sample with carbon monoxide was studied, and a conclusion on dissimilar states of oxygen bound to gallium was drawn.