Coordination behavior of the core and valence levels of low-coordinated oxygen ions on the surface of magnesium oxide

For low-coordinated (N=2,3,4,5) oxygen ions on the surface and in the bulk of magnesium oxide, the behavior of the core O1s- and valence O2s-, O2p-levels is considered. The MgO ₆ ¹⁰⁻ , OMg ₆ ¹⁰⁺ , Mg₁₃O ₁₄ ²⁻ , O₁₃Mg ₁₄ ²⁺ , Mg₄O ₇ ⁶⁻ , and OMg ₂ ²⁺ clusters are calculated by the SCF-Xα-SW method. The binding energies of oxygen 1s-, 2s-, and 2p-states decrease with coordination. This coordination dependence is explained by the greater change of the Madelung potential as compared to variations of the purely electronic terms of the binding energies of oxygen ions. The dependence of oxygen atomic charges and relaxation energies on coordination is also discussed. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 1, pp. 16–26, January–February, 1995. Translated by the authors     

A novel three-dimensional coordination polymer [Cd2(C3H2O4)2(H2O)2(μ 2-hmt)] n (hmt = hexamethylenetetramine): synthesis and crystal structure

The self-assembly of the Cd^II ion, hexamethylenetetramine (hmt) and malonate ligand yields a three-dimensional (3D) coordination polymer [Cd₂(C₃H₂O₄)₂(H₂O)₂( ₂-hmt)] _n with channels. The Cd^II ion is located in a octahedral coordination environment, composed of four oxygen atoms from three malonates, one oxygen atom of water and one nitrogen atom of hmt. Two oxygen atoms of each malonate coordinate to the same Cd^II ion and the other two oxygen atoms connect to adjacent two Cd^II ions respectively to form a two-dimensional infinite network, these networks are bridged by ₂-hmt coordinated to Cd^II ions to product a 3D architecture.     

Preparation and crystal structure of a nickel (II)-Uranyl(VI) binuclear chelate

Summary The structure of the heterobinuclear complex of Ni²⁺ and [U02₂]²⁺ with the tetraanionic ligand derived from the condensation of 1,2-diaminoethane with o-acetoacetylphenol has been determined from diffractometer data and refined to R = 7.2%. The crystals are monoclinic, P21 /a, with = 20.65(2), b = 8.58(1), c = 14.68(2) Å and = 97.78(5); Z = 4. The ligand employed has two different coordination sets of atoms, N₂O₂ and O₂O₂, two oxygen atoms being common to both donor sets. In the complex the nickel ion, which is four coordinate but not square planar, is retained in the inner N₂O₂ chamber, whilst the uranyl ion is incorporated in the outer O₂O₂ chamber. A molecule of solvent is retained to preserve the preferred seven coordination of uranium.     

Oxygen diffusion in SrCe<Subscript>0.95</Subscript>Yb<Subscript>0.05</Subscript>O<Subscript>3−δ</Subscript>

¹⁸O/¹⁶O isotope exchange depth profiling (IEDP) combined with secondary ion mass spectrometry (SIMS) has been used to measure the oxygen tracer diffusivity of SrCe_0.95Yb_0.05O_3– between 800 °C and 500 °C at a nominal pressure of 200 mbar. The values of D* (oxygen tracer diffusion coefficient) and k (surface exchange coefficient) increase steadily with increasing temperature, and the activation energies are 1.13 eV and 0.96 eV, respectively. Oxygen ion conductivities have been calculated using the Nernst–Einstein equation. The transport number for oxide ions at 769 °C, the highest temperature studied, is only ~0.05. Moreover, SrCe_0.95Yb_0.05O_3– has been studied using impedance spectroscopy under dry O₂, wet O₂ and wet H₂ (N₂/10% H₂) atmospheres, over the range 850–300 °C. Above ~550 °C, SrCe_0.95Yb_0.05O_3– shows higher conductivity in dry O₂ than in wet O₂ or wet H₂; below that temperature the results obtained for the three atmospheres are comparable. Dry O₂ shows the highest activation energy (0.77 eV); the activation energies for wet O₂ and wet H₂ are identical (0.62 eV).Abbreviations HTPC high-temperature proton conductor - IEDP isotope exchange depth profiling - SIMS secondary ion mass spectrometryPresented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

Electron attachment to oxygen and oxygen/ozone clusters studied in a high-resolution crossed beams experiment

Highly monochromatized electrons (with 30 meV FWHM) are used in a crossed beams experiment to investigate electron attachment to oxygen clusters (O₂)_n at electron energies from approximately zero eV up to 2 eV. At energies close to zero the attachment cross section for the reaction (O₂)_n +e → O ₂ ^? varies inversely with the electron energy, indicative of s-wave electron capture to (O₂)_n. Peaks in the attachment cross section present at higher energies can be ascribed to vibrational levels of the oxygen anion. The vibrational spacings observed can be quantitatively accounted for. In addition electron attachment to mixed oxygen/ozone clusters has been studied in the energy range up to 4 eV. Despite the initially large excess of oxygen molecules in the neutral clusters the dominant attachment products are undissociated cluster ions (O₃) _m ^? including the O ₃ ^? monomer while oxygen cluster ions (O₂) _n ^? appear with comparatively low intensity.     

Mechanisms of anion formation in O2, O2/Ar and O2/Ne clusters; the role of inelastic electron scattering

Measurements are reported on the formation of negative ions in O₂, O₂/Ar and O₂/Ne clusters aimed at establishing the mechanisms of anion formation and the role of inelastic electron scattering by the cluster constituents on negative ion formation in clusters. In the case of pure O₂ clusters the main anions we detected are of two types: O^–(O₂) _n0 and (O₂) _n ^1– . The yields of O^–(O₂) _n showed maxima at 6.3, 8.0 and 14.0 eV and the data suggest O^– as their precursor; the maxima at 8 and 14 eV are due to the production of O^– via symmetry forbidden dissociative attachment processes in O₂ at these energies which become allowed in clusters. The yields of (O₂) _n ^– showed a strong maximum at near-zero energy (0.5 eV) and also at 6.3, 8 and 14 eV. With the exception of the near-zero energy resonance, the (O₂) _n ^– anions at 6.3, 8 and 14 eV are attributed to nondissociative attachment of near-zero energy secondary electrons to O₂ clusters. The slow secondary electrons result predominantly from scattering via the O ₂ ^– negative ion states of incident electrons with energies in their respective regions. Similar results were obtained for the mixed O₂/rare gas clusters except that now a feeble and distinctly structured contribution in the yields of O^–(O₂) _n , (O₂) _n ^– (and Ar(O₂) _n ^– ) was observed at energies >10 eV. These anions are believed to have the lowest negative ion states of Ar*^– (Ne*^–) as their precursors.     

The reduction of oxygen in molten lithium carbonate

Oxygen reduction on immersed gold electrodes has been studied in Li₂CO₃ melt under steady-state conditions and by the potential-sweep method. Reaction order measurements have established that the species being reduced is not molecular oxygen, but the peroxide ion. The latter is in chemical equilibrium with molecular oxygen and oxide ions. The rate-determining step is the primary charge transfer

where (O^?) is a transient species. The exchange current densities and activation energies have been determined. Under conditions where O₂^2? diffusion is not limiting (e.g. meniscus electrodes) the rate of neutralization of oxide by CO₂ at the electrode surface is probably rate-determining.     

Zur Struktur von zwei Hydraten des Natriumphenolats: C6H5ONa · H2O und C6H5ONa · 3 H2O

The Structures of two Hydrates of Sodium Phenoxide: C₆H₅ONa · H₂O and C₆H₅ONa · 3 H₂O In the monohydrate of sodium phenoxide sodium is coordinated by 4 oxygen atoms having an average distance Na? O of about 2.631 Å being arranged in form of a distorted tetrahedron. The oxygen atoms of water and phenoxid serve as bridging ligands. Hence, the structure can be considered as a network with a general formula [Na^[4]O]. Moreover, the oxygen atoms are linked via hydrogen bonding. In the trihydrate of sodium phenoxide sodium is surrounded with 5 oxygen atoms with an average distance of 2.39 Å forming a tetragonal pyramide. The oxygen of the phenoxide, however, does not participate in the coordination of the sodium ion. The coordination polyhedrons are connected by sharing edges and verteces. The resulting layer can be described by the general formula [Na^[5]O₂^[2]O^[2]O^[1]]. Via hydrogen bonding the phenoxide ions are attached to this layer.     

Quantum-chemical investigation of the localization and hydration of Ca<Superscript>2+</Superscript> and Mg<Superscript>2+</Superscript> cations in eight- and ten-fold structural rings in the clinoptilolite structure

The hydration of Ca²⁺ and Mg²⁺ exchange cations in solution and in 10- and 8-membered silicon—oxygen rings of the clinoptilolite was studied by ab initio and MNDO quantum-chemical methods. The coordination numbers of these cations with respect to water molecules and their hydration energies were determined. It is shown that the localization of Ca²⁺ and Mg²⁺ in the clinoptilolite structure was different for the dehydrated state and the partially hydrated state. The ion exchange sorption energy calculated for the Ca²⁺—Mg-Cli system was in satisfactory agreement with the experimental data.Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 40, No. 6, pp. 357–362, November–December, 2004.