Ab initio surface phase diagram of the {104} calcite surface

Electronic structure calculations, performed at the density functional theory level, were employed to study the surface termination of the {104} calcite surface in contact with a gaseous phase containing water and carbon dioxide. A surface phase diagram was generated to investigate the change in surface termination as a function of temperature, pressure, and gas-phase composition. This diagram revealed that a nonstoichiometric termination could occur in atmospheric conditions at high relative humidity, hence suggesting that nonstoichiometric surfaces can play a major role in the chemistry of calcite surfaces.     

Divalent Cd and Pb uptake on calcite {1014} cleavage faces: an XPS and AFM study

The interaction of divalent Cd and Pb with the {101 4} cleavage faces of calcite has been investigated with X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Analysis of the {101 4} cleavage planes of calcite was carried out with X-ray photoelectron spectroscopy (XPS) after exposure to divalent metal-bearing solutions in the 0.1-100 microM concentration range for times ranging from 1 to 24 h. The uptake of Cd2+ by calcite was determined to be greater than that of Pb2+ under similar experimental conditions (1 microM, pH 8.2, 24 h exposure time). In both cases, the majority of the divalent metal was postulated to exist in a surface precipitate. AFM results showed that the exposure of calcite to a 1 microM Pb2+ solution resulted in ellipsoidal surface growths that were attributed to the nucleation of a PbCO3 bulk phase. In the Cd circumstance, AFM showed comparatively flat growth features forming on the calcite surface even at concentrations down to 0.1 microM, where the solution would be expected to be undersaturated with respect to Cd bulk phases. These features were attributed to a (Ca,Cd)CO3 solid solution. The individual exposure of these Cd/CaCO3 and Pb/CaCO3 samples to water pre-equilibrated with calcite (metal free) for 1 h led to the removal of no more than 20% of the divalent metal, suggesting that if there was an adsorbed Pb or Cd complex initially on the calcite surface, it was an minority species compared to the precipitate phase. Exposure of calcite to 100 microM Cd and Pb resulted in the accumulation of precipitate on the calcite surface presumably due to the divalent metal initial solution concentrations exceeding the solubility products of CdCO3 and PbCO3, respectively.     

Controlling transformations in the assembly of polyoxometalate clusters: {Mo11V7}, {Mo17V8} and {Mo72V30}

The reaction of molybdate with vanadium(V) in the presence of sulfite anions is explored showing how, via cation control, stepwise assembly through the {Mo(11)V(7)} cluster yields a {M(25)} cluster-based compound, [Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(μ(9)-SO(3))(Mo(VI)(6)V(V)O(22))](10-) (1a), which was first discovered using cryospray mass spectrometry, whereas switching the cation away from ammonium allows the direct formation of the spherical 'Keplerate' {Mo(72)V(30)} cluster.     

Formation of gold surfaces with a strongly preferred {100}-orientation

Gold surfaces with a strongly preferential Au{100} orientation were prepared by annealing of commercial gold foil in an oven at temperatures between 400 and 900 °C. The annealing also led to an improved crystallinity and growth of grain size. A similar surface restructuring was observed upon ultrasonication of the gold foil at room temperature in a water bath.     

Nitrogen adsorption and desorption at iron pyrite FeS2{100} surfaces

We have investigated the interaction of nitrogen with single-crystal iron pyrite FeS(2){100} surfaces in ultra-high vacuum. N(2) adsorbs molecularly at low temperatures, desorbing at 130 K, but does not adsorb dissociatively even at pressures up to 1 bar. Atomic surface N can, however, be obtained with nitrogen ions and/or excited neutral species, generated by passing N(2) through an ion gun. Substantial nitrogen-induced disorder is seen with both ions and neutrals, and no ordered N overlayers form; a decrease in the S/Fe ratio is seen when exposing to nitrogen ions. Recombinative desorption leads to temperature-programmed desorption peaks at 410 and 520-560 K which we associate with interstitial atomic N and substitutional ionic N, respectively, in the surface regions. Thermal repair of sputter damage necessitates segregation of bulk S to the surface, which, over repeated experiments, leads to gross cumulative damage to the bulk crystal. The desorption temperatures associated with recombinative desorption of atomic N from FeS(2){100} are significantly lower than those measured for Fe surfaces. This is linked to the inability of FeS(2){100} to dissociate N(2), but suggests that N(ads) will be significantly more able to react with other species than it is on Fe surfaces.     

Preparation of monocrystalline Pt microelectrodes and electrochemical study of the plane surfaces cut in the direction of the {111} and {110} planes

2-Cyano-1-methylpyridinium ion, I, exhibits three well-defined polarographic waves in Britton-Robinson buffer at pH 5 to 8. Electrolysis at the plateau potential of the most positive wave, involving a one-electron uptake, leads to the formation of a pyridinyl radical which probably dimerizes to a 2,4′-linked structure, VIII. Electrolysis at the plateau potential of the second wave, involving a number of electrons variable between nearly 4 (at pH≈5) and ≈3 (at pH≈8), leads to the formation of a mixture of 2-aminomethyl-1-methylpyridinium ion and 1-methylpyridinium ion. At the third wave potentials the second wave products are further reduced to give basic species with catalytic activity.     

Trading templates: supramolecular transformations between {CoII13} and {CoII12} nanoclusters

"Nuclearity switching" from a {Co13} supercluster to a {Co12} species via the addition of CO(3)2- anions is reported and can be traced in solution using electrospray MS techniques. In addition, cryospray MS can be used to identify the entire cluster in solution despite the relative lability of its constituents.     

Assembly of a family of mixed metal {Mo:V} polyoxometalates templated by TeO3(2-): {Mo12V12Te3}, {Mo12V12Te2} and {Mo17V8Te}

The influence of the pyramidal heteroanion, TeO(3)(2-) in the self-assembly of mixed metal (Mo/V) systems, is demonstrated by the isolation of three novel mixed-metal, mixed-valence architectures, {Mo(12)V(12)Te(3)} (1), {Mo(12)V(12)Te(2)} (2) and {Mo(17)V(8)Te} (3) with the tellurium centres exhibiting the novel μ(8)-TeO(4) and μ(9)-TeO(3) coordination modes while compounds 1 and 2 were discovered utilizing ESI mass spectrometry.     

Infrared Spectroscopy of \hbox {CH}_4/\hbox {N}_{2} and \hbox {C}_{2}\hbox {H}_{m}/\hbox {N}_{2} ({m = 2, 4, 6}) Gas Mixtures in a Dielectric Barrier Discharge

Fourier transform infrared spectroscopy of \(\hbox {CH}_{4}/\hbox {N}_{2}\) and \(\hbox {C}_{2}\hbox {H}_{m}/\hbox {N}_2\) ( \(m = 2, 4, 6\) ) gas mixtures in a medium pressure (300 mbar) dielectric barrier discharge was performed. Consumption of the initial gas and formation of other hydrocarbon and of nitrogen-containing HCN and \(\hbox {NH}_{3}\) molecules was observed. \(\hbox {NH}_{3}\) formation was further confirmed by laser absorption measurements. The experimental result for \(\hbox {NH}_{3}\) is at variance with simulation results.     

Structural,magnetic and magnetocaloric properties of $$\hbox {Ni}_{54}\hbox {Mn}_{14}\hbox {Ga}_{27}\hbox {Fe}_{5}$$ Ni 54 Mn 14 Ga 27 Fe 5 : the impact of annealing time

Journal of Thermal Analysis and Calorimetry - The structural, magnetic and magnetocaloric properties of $$\hbox {Ni}_{54}\hbox {Mn}_{14}\, \hbox {Ga}_{27}\hbox {Fe}_{5}$$ Heusler alloy as a...     

Density functional theory study of the structures and stabilities of CuO\documentclass{article}\pagestyle{empty}\begin{document}$_{3}^{-}$\end{document} and CuO3

Hybrid density functional theory calculations on the structures, vibrational frequencies, electron binding and dissociation energies, and bonding properties of CuO$_{3}^{-}$ and CuO₃ species have been carried out. Stable isomers containing an O₃ subunit and composed of O₂ bound to CuO have been located on the potential energy hypersurfaces of CuO$_{3}^{-}$ and CuO₃. The isomers formed by O₂ bonded to CuO in side‐on and end‐on coordination are more stable than those containing an O₃ subunit. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 162–168, 2001     

Synthesis and Characterization of 1,3,2‐Bis (arylamino) phospholidine, 2‐oxide Derivatives: Crystal Structures of $\rm Cl(O)\overline{PN(p-Me-C_{6}H_{4})CH_{2}CH_{2}N}(p-Me-C_{6}H_{4})$ and $\rm ((CH_{2}C_{6}H_{5})(O)\overline{PN(p-Me-C_{6}H_{4})CH_{2}CH_{2}N}(p-Me-C_{6}H_{4})$

Using phosphoryl chloride as a substrate, a family of 1,3,2‐bis(arylamino) phospholidine, 2‐oxide of the general formula ; (X=Cl, 6a ; X=NMe₂, 1b ; X=N(CH₂C₆H₅)(CH₃), 2b ; X=NHC(O)C₆H₅, 3b ; X=4Me‐C₆H₄O, 4b ; X=C₆H₅O, 5b ; X=NHC₆H₁₁, 6b ; X=OC₄H₈N, 7b ; X=C₅H₁₀N, 8b ; X=NH₂, 9b ; X=F, 10b and Ar=4Me‐C₆H₄) was prepared and characterized by ¹H, ¹⁹F, ³¹P and ¹³C NMR and IR spectroscopy, and elemental analysis. A general and practical method for the synthesis of these compounds was selected. The structures of 6a and 2b were determined by single‐crystal X‐ray diffraction techniques. The low temperature NMR spectra of 2b revealed the restricted rotation of P‐N bond according to two independent molecules in crystalline lattice.     

On the calculation of arbitrary multielectron molecular integrals over Slater‐type orbitals using recurrence relations for overlap integrals. III. Auxiliary functions \documentclass{article}\pagestyle{empty}\begin{document}$Q_{nn'}^{q}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$G_{-nn'}^{q}$\end{document}

The auxiliary functions $Q_{nn'}^{q}(p,pt)$ and $G_{-nn'}^{q}(p_{a},p,pt)$ which are used in our previous paper [Guseinov, I. I.; Mamedov, B. A. Int J Quantum Chem 2001, 81, 117] for the computation of multicenter electron‐repulsion integrals over Slater‐type orbitals (STOs) are discussed in detail, and the method is given for their numerical computation. The present method is suitable for all values of the parameters p_a, p, and pt. Three‐ and four‐center electron‐repulsion integrals are calculated for extremely large quantum numbers using relations for auxiliary functions obtained in this paper. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Kinetics of dissociative adsorption on stepped surfaces of platinum

The kinetics of dissociative adsorption of oxygen was studied by the Monte Carlo method for a model which supposed that absorption occurs with a high rate only on steps and that O_ads may migrate from steps onto terraces and backward. At the relatively low activation energy of diffusion from steps onto terraces E_dif∼ 75 kJ/mol (E_dif is lower by 4 kJ/mol in the back direction), the function log(s(θ)), wheres is the sticking coefficient and θ is the surface coverage by oxygen atoms, is almost linear at 300 K; that is, the Roginskii-Elovich adsorption equation is obeyed. If it is supposed that the bonding energy of adatoms on terraces is slightly higher than that on steps, and the sticking coefficient is constant and equal to s₀ up to high degrees of coverage as well as in the model of the kinetics of adsorption with a precursor state. Deceased.