Production and collision-induced dissociation of gas-phase, water- and alcohol-coordinated uranyl complexes containing halide or perchlorate anions

Electrospray ionization was used to generate mono-positive gas-phase complexes of the general formula [UO2A(S)n]+ where A = OH, Cl, Br, I or ClO4, S = H2O, CH3OH or CH3CH2OH, and n = 1-3. The multiple-stage dissociation pathways of the complexes were then studied using ion-trap mass spectrometry. For H2O-coordinated cations, the dissociation reactions observed included the elimination of H2O ligands and the loss of HA (where A = Cl, Br or I). Only for the Br and ClO4 versions did collision-induced dissociation (CID) of the hydrated species generate the bare, uranyl-anion complexes. CID of the chloride and iodide versions led instead to the production of uranyl hydroxide and hydrated UO2+. Replacement of H2O ligands by alcohol increased the tendency to eliminate HA, consistent with the higher intrinsic acidity of the alcohols compared to water and potentially stronger UO2-O interactions within the alkoxide complexes compared to the hydroxide version.     

Determination of order parameter of YMn0.5Fe0.5O3 epitaxial thin films by anomalous X-ray scattering technique

The crystal structure of an orthorhombic YMn_0.5Fe_0.5O₃ (010) (YMFO) epitaxial films on YAlO₃(010) substrate was studied using X-ray diffraction, X-ray absorption spectroscopy, and anomalous X-ray diffraction techniques. Due to the utmost similar scattering factors of Mn and Fe atoms, it is hard to distinguish them at specific sites of the unit cell from the variations in the diffraction peak intensity. Therefore, anomalous X-ray scattering was used to determine the order or disorder structure of YMFO films. To estimate the order parameter of the YMFO film, the incident X-ray energies have been scanned around the Mn K-edge and Fe K-edge, resulting in enhanced diffraction intensities of the forbidden YMFO (010) peak by 15–20 times, respectively. This in turn revealed that YMFO films have a partially ordered structure of about 40 ± 10% in the epitaxially grown thin film.     

Electrochemical synthesis and the functionalization of few layer graphene in ionic liquid and redox ionic liquid

Electrochemical reductive exfoliation of graphite to few layered graphene(FLG) in presence of 1-ethyl-2,3-dimethyl imidazolium bis(trifluoromethylsulfonyl) imide ionic liquid and redox ionic liquid based ferrocene has been investigated. Thus, by applying a mild negative potential(-2.7 V vs. Fc/Fc~+) to carbon electrode in ionic liquid graphene flakes could be generated. The generated materials have been characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, high resolution transmission electron microscopy and atomic force microscopy. XPS and Raman analysis show that the electrochemical reductive exfoliation provides the formation of FLG. The thickness of the resulting FLG was found to be ranged between 4 and1 nm. HR-TEM images reveal the formation of few graphene layers and in some cases single graphene layer was observed.Moreover, this electrochemical route conduces to the formation of ionic liquid functionalized FLG. Finally, the reductive exfoliation was further investigated in the presence of redox ionic liquid. XPS and electrochemical measurements confirm the presence of ferrocene.     

Infrared, optical absorption, and EPR spectroscopic studies on natural gypsum

The natural gypsum has been investigated by infrared, Raman, X-ray diffraction, optical absorption and electron paramagnetic resonance spectroscopy. The fundamental stretching and bending vibrations observed in the infrared region for SO₄²⁻ and H₂O are compared with the near-infrared overtones and combinations of these vibrations. MIR and Raman spectral features are attributed to sulfate fundamentals and lattice vibrations of H₂O, SO₄²⁻. The charge transfer and ligand field transition bands were observed near 490, 630, and 800–900 nm and were compared to those of iron oxides. The optical absorption spectrum indicates the presence of ferric and ferrous ions in the mineral. The site symmetry of Fe(III) in the sample is tetragonally distorted. EPR results indicate the presence of the ferric ion in a tetragonally distorted state.     

Intrinsic hydration of monopositive uranyl hydroxide,nitrate, and acetate cations

The intrinsic hydration of three monopositive uranyl-anion complexes (UO(2)A)(+) (where A = acetate, nitrate, or hydroxide) was investigated using ion-trap mass spectrometry (IT-MS). The relative rates for the formation of the monohydrates [(UO(2)A)(H(2)O)](+), with respect to the anion, followed the trend: Acetate > or = nitrate > hydroxide. This finding was rationalized in terms of the donation of electron density by the strongly basic OH(-) to the uranyl metal center, thereby reducing the Lewis acidity of U and its propensity to react with incoming nucleophiles, viz., H(2)O. An alternative explanation is that the more complex acetate and nitrate anions provide increased degrees of freedom that could accommodate excess energy from the hydration reaction. The monohydrates also reacted with water, forming dihydrates and then trihydrates. The rates for formation of the nitrate and acetate dihydrates [(UO(2)A)(H(2)O)(2)](+) were very similar to the rates for formation of the monohydrates; the presence of the first H(2)O ligand had no influence on the addition of the second. In contrast, formation of the [(UO(2)OH)(H(2)O)(2)](+) was nearly three times faster than the formation of the monohydrate.     

A study of thermal and dielectric behavior of melaminium perchlorate monohydrate single crystals

Single crystals of melaminium perchlorate monohydrate (MPM) have been grown from aqueous solution by slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms the title crystal crystallizes in the triclinic (P-1) structure and the calculated lattice parameters are a = 5.6275 ± 0.0780 Å, b = 7.6926 ± 0.1025 Å, c = 12.0878 ± 0.2756 Å, α = 103.89 ± 1.01°, β = 94.61 ± 0.92°, γ = 110.22 ± 0.81°, and V = 468.95 Å³. The thermal decomposition behavior of MPM has been studied by means of thermogravimetric analysis at three different heating rates 5, 10, and 20 °C min^?1. The values of effective activation energy (E _a), pre-exponential factor (ln A) of each stage of thermal decomposition for all heating rates were calculated by model free method: Kissinger, Kim–Park, and Flynn–Wall method. A significant variation of effective activation energy (E _a) with conversion (α) indicates that the process is kinetically complex. The linear relationship between the A and E _a values was established (compensation effect). Dielectric study has also been carried out and it is found that both dielectric constant (ε′) and dielectric loss (ε″) decreases with increase in frequency.