Rapid chromite dissolution using manganese dioxide-lithium-sulphate-sulphuric acid mixture-estimation of alumina in chromite for quality control assessment

Proposed in this paper is a less labour-intensive method involving a mixture (0.3 g MnO₂ + 1.0 g Li₂SO₄ + 10 mL H₂O + 20 mL of 36M H₂SO₄ for 0.2 g sample) to decompose chromites for accurate and precise estimation of alumina in chromite matrices for quality control (QC) assessment. Several international chromite samples, namely, CHR-BKg, CHR-Pt, IGS-30 and BCS-308 were analysed. Intermethod comparison studies reveal that the probability of results being different is less than (slight variation in case of CHR-BKg) 99% when two methods [ethylenediamine tetraacetic acid (EDTA) titration and spectrophotometry using ammonium aurinitricarboxylate (aluminon)] were compared. It also shows that the proposed method yields better results than the most conventional route involving HClO₄ decomposition used for similar purpose; hence can be used for QC programme and in the evaluation of reference materials.     

Localized molecular orbital studies in momentum space. I. compton profiles of 1s core electrons and hydrocarbons

The calculations of momentum space properties for the polyatomic molecules CH₄, C₂H₄ and C₂H₆ using localized molecular orbitals of double zeta quality basis sets are presented. The LMO analysis shows that localized and canonical core electrons have different momentum space properties, and that in agreement with the experimental data of Eisenberger and Marra one can distinguish the momentum properties of the CC single and double bonds. The effect of environment on a bond is seen by comparing the CH bond in these three molecules.The concept of electron pair size is introduced as a quantitative guide for interpreting momentun space properties.     

Thermodynamics of the system H2O−NaCl−Na2SO4−MgSO4 to the saturation limit of NaCl at 25°C

Isopiestic results are reported for the quaternary system H₂O–NaCl–Na₂SO₄–MgSO₄. The excess free energies for mixing the double salt Na₂ Mg(SO₄)₂ with NaCl are fairly large and negative, as also are the free energies for mixing the three salts to form the quaternary aqueous system.     

Electron correlation theories and their application to the study of simple reaction potential surfaces

This paper serves two purposes. The first is to describe an implementation of the coupled cluster theory with double substitutions (CCD ) previously developed by Cizek. The second is to apply this method and closely related fourth-order perturbation methods to some simple molecules and reaction potential surfaces. These studies show that CCD theory gives results close to those of a Møller-Plesset perturbation treatment to fourth order in the space of double and quadruple substitutions MP 4(DQ). Addition of contributions from single substitutions at fourth order makes little change in predicted relative energies. Preliminary results on the potential surfaces for 1,2-hydrogen shifts in C₂H₂, HCN, CH₂O, and N₂H₂ are discussed and compared with previous studies.     

Mononuclear oxidodiperoxido vanadium(V) complex: synthesis,structure, VHPO mimicking oxidative bromination,and potential detection of hydrogen peroxide

An oxidodiperoxidovanadium(V) complex, (NH₄)[VO(O₂)₂(phen)](H₂O)₂, has been synthesized and structurally characterized. The complex crystallizes in the P2₁/c space group. The vanadium center is seven-coordinate with pentagonal bipyramidal geometry. The compound was designed in order to develop a VHPO mimic, so it was tested for VHPO activity through the single pot bromination of phenol red to bromophenol blue whereby, it afforded positive response to establish that the complex is indeed a VHPO mimic. In addition, the compound is capable of detection of H₂O₂.     

Syntheses and structural determination of eight-coordinate Na[YbIII(Cydta)(H2O)2] · 5H2O and [YbIII(Hegta)] · 2H2O complexes

Na[Yb^III(Cydta)(H₂O)₂] · 5H₂O (1) (H₄Cydta = trans-1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid) and [Yb^III(Hegta)] · 2H₂O (2) (H₄egta = ethyleneglycol-bis-(2-aminoethylether)-N,N,N′,N′-tetraacetic acid) were prepared and their composition and structures were determined by elemental analyses and single-crystal X-ray diffraction techniques. Complex 1 crystallized in the triclinic crystal system with space group P 1; the Yb^III is eight-coordinate by a hexadentate Cydta and two water molecules. Complex 2 is a protonated egta complex, crystallized in the monoclinic crystal system with space group P 2 ₁ /c; Yb^III is coordinated only by the octadentate Hegta ligand. Both these complexes adopt a pseudo-square antiprismatic conformation.     

Diagramme Polythermique Du Systeme Ternaire KCl–FeCl2–H2O Entre 0 Et 70°C

Polytherm diagram of the ternary system KCl–FeCl₂ –H₂ O between 0 and 70°C. Phase equilibria in the KCl–FeCl₂ –H₂ O system were studied over the temperature range 0–70°C by conductimetric and analytical methods. A solubility polytherm of the system was constructed. We have observed the crystallization fields of the KCl and FeCl₂ 6H₂ O (at 0°C), KCl and FeCl₂ 4H₂ O (at 15, 30 and 40°C) and KCl, FeCl₂ 4H₂ O and of a double salt KClFeCl₂ 2H₂ O are obtained at 70°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

A complete experimental approach for synthesis gas separation studies using static gravimetric and column breakthrough experiments

In this work a combination of static gravimetric and inverse chromatographic techniques is used to study the adsorption and separation of the main synthesis gas components, i.e. CO₂, CO, CH₄ and H₂. The single component adsorption isotherms of CO₂, CO, CH₄ and H₂ on faujasite NaX were measured from 303 K to 473 K and over a large range of pressures (from 0 to 1200 kPa). Breakthrough curves of CO₂ and CO and their mixtures were determined at 323 K and 373 K and 100 kPa as an illustrative example. A nice agreement was noticed between the two above-mentioned techniques for single component adsorption. Binary mixture dynamics measurements were compared to the predictions of ideal adsorption solution theory (IAST) via the previously cited single component adsorption data.     

Pulse radiolysis study of trapped electron in MgSO4.7H2O single crystal

The single crystal of MgSO₄.7H₂O is very interesting to study the structure and kinetics of trapped electron in solids, because the hydrated salt has many H₂O molecules in the crystal lattice like water. The pulse radiolysis study of the trapped electrons in MgSO₄.7H₂O single crystal was carried out based on an electron linear accelerator. Two optical absorption peaks of the trapped electron in MgSO₄.7H₂O single crystal were observed: one is at the wavelength of 600 nm with a short lifetime of 81.4 ns; another is at 400 nm with a long lifetime of 1.06 μs. The kinetics of the trapped electron in the crystal was also compared with that in the aqueous solution.     

(Z)‐2‐(3‐Methoxy­benzyl­idene)‐1‐aza­bicyclo­[2.2.2]octan‐3‐one

The crystal structure of the title compound, C₁₅H₁₇NO₂, contains two nearly identical but crystallographically independent mol­ecules, each with a double bond connecting an aza­bicyclic ring system to a 3‐methoxy­benzyl­idene moiety. The space group is triclinic P. The benzene ring is twisted by 18.44 (5) and 22.35 (4)° with respect to the plane of the double bond connected to the azabicyclic ring system for the two mol­ecules. In addition to C—H⋯π inter­actions, mol­ecules are held together in the solid state by van der Waals inter­actions.     

Applicability of quasi-degenerate many-body perturbation theory to quasi-degenerate electronic states: The H4 model revisited

The performance of the quasi-degenerate many-body perturbation theory up to the third order is investigated for the ground state, five excited states, and the first quintet of a simple four-electron H₄ model system consisting of two stretched hydrogen molecules, in which the degree of quasi-degeneracy can be continuously varied from a nondegenerate to a full degenerate situation. We employ a DZP basis set. The effect of intruder states is considered and a comparison with other multireference correlation techniques is also provided. Finally, a criterion for the model space to be quasi-degenerate will be reformulated and generalized. © 1995 John Wiley & Sons, Inc.     

Transition metal tetramolybdate dihydrates MMo4O13·2H2O (M=Co,Ni) having a novel pillared layer structure

Hydrothermal synthesis in the M/Mo/O (M=Co,Ni) system was investigated. Novel transition metal tetramolybdate dihydrates MMo₄O₁₃·2H₂O (M=Co,Ni), having an interesting pillared layer structure, were found. The molybdates crystallize in the triclinic system with space group P−1, Z=1 with unit cell parameters of a=5.525(3) Å, b=7.058(4) Å, c=7.551(5) Å, α=90.019(10)°, β=105.230(10)°, γ=90.286(10)° for CoMo₄O₁₃·2H₂O, and a=5.508(2) Å, b=7.017(3) Å, c=7.533(3) Å, α=90.152(6)°, β=105.216(6)°, γ=90.161(6)° for NiMo₄O₁₃·2H₂O The structure is composed of two-dimensional molybdenum-oxide (2D Mo-O) sheets pillared with CoO₆ octahedra. The 2D Mo-O sheet is made up of infinite straight ribbons built up by corner-sharing of four molybdenum octahedra (two MoO₆ and two MoO₅OH₂) sharing edges. These infinite ribbons are similar to the straight ones in triclinic-K₂Mo₄O₁₃ having 1D chain structure, but are linked one after another by corner-sharing to form a 2D sheet structure, like the twisted ribbons in BaMo₄O₁₃·2H₂O (or in orthorhombic-K₂Mo₄O₁₃) are.     

A ytterbium polymer incorporating ethyl-4,5-imidazole-dicarboxylate and formate coligand: Structure, luminescent, and magnetic properties

A new lanthanide-organic coordination polymer incorporating both substituted imdazole dicarboxylate and formate auxiliary ligand, namely {[Yb₃(HEimda)₄(μ₂-HCOO) · 4H₂O] · 2H₂O} _n (I) (H₃Eimda = 1H-2-ethyl-4,5-imidazole-dicarboxylic acid), has been prepared and was structurally characterized by elemental analysis, IR and X-ray diffraction. It crystallizes in the monoclinic system, space group of C2/c. The polymer I is built from two dimensional (2D) double decker networks based on the Ln₄HEimda₄ tetranuclear basic carboxylate as secondary building unit. The extensive hydrogen bonds extend the 2D lamellar network into a 3D supramolecular aggregate. The emission spectrum of polymer I exhibits ligand-to-metal charge-transfer luminescence. Variable-temperature magnetic susceptibility measurement reveals that the end to end bridging fashion of formate group results in the depopulation of the stark levels for a single Yb³⁺ ion and/or possible antiferromagntic interactions between Yb³⁺ ions within the carboxylato bridged dinuclear unit.     

Reactivity investigations of some chosen peroxo-vanadium(V), manganese(III) and chromium(VI) compounds

An interpretative account of the results of reactions in aqueous medium of a highly peroxygenated vanadium(V) complex, K [V(O_{2 3}]·3H₂O, with different organic and inorganic substrates is presented. The reactions were monitored by solution EPR spectroscopy and isolation of products at different stages of the reactions. Redox reactions between diperoxide, K[VO(O₂)₂(H₂O)] and VOSO₄ were conducted. The results of the investigation suggest that secondary oxygen exchange-reaction occurs which not only depends on but also utilises the intermediates in the primary reaction during diperoxovanadate-dependent oxidation of VOSO₄. In an interesting reactiontris(acetylacetonato)-manganese(III), Mn(acac)₃, on being reacted with a hydrogen peroxide adduct, KF·H₂O₂, and bpy and phen afforded crystalline [Mn(acac)₂(bpy)] and [Mn(acac)₂(phen)], respectively. The X-ray structural analysis of [Mn(acac)₂(phen)] showed that the compound crystallised in orthorhombic space groupPbcn. The structure consists of a pseudooctahedral Mn(II) ion being bound to two acac⁻(C₅H₅O ₂ ⁻ ) and a phen ligand with the molecule lying on two-fold axis. Reactivity profiles of two new chromium(VI) reagents viz., pyridinium fluorochromate, C₅H₅NH[CrO₃F] (PFC), and quinolinium fluorochromate C₉H₇NH [CrO₃F] (QFC), have been presented. The compounds are capable of acting as both electron-transfer and oxygen-atom-transfer agents. The X-ray analysis of PFC crystals reveals that the compound crystallises in the orthorhombic space group CmcZ₁. The structure consists of discrete pyridinium cations and CrO₃ F anions with no significant hydrogen bonding. This results in total disorder of the pyridinium cation. The tetrahedral [CrO₃ F]⁻ ion lies on a crystallographic mirror plane.     

Intermolecular hydrogen bonding in the binary mixture [(C2H5)2CO + CH3OH] probed by polarized Raman measurements and DFT calculations

The Raman spectra of neat (C₂H₅)₂CO (pentanone) and its binary mixtures with hydrogen donor solvent (CH₃OH), [(C₂H₅)₂CO + CH₃OH] having different mole fractions of the reference system, (C₂H₅)₂CO in the range 0.1-0.9 at a regular interval of 0.1 were recorded in the CO stretching region. In neat liquid, the Raman peak appears asymmetric. The asymmetric nature of the peak has been attributed to the CO stretching mode of the two conformers of (C₂H₅)₂CO having C₂ and C_2v point groups and the corresponding bands at ∼1711 and ∼1718 cm⁻¹, respectively. A careful analysis of the I_iso (isotropic component of the Raman scattered intensity) at different concentrations reveals that upon dilution with methanol, at mole fraction C = 0.6, an additional peak in the CO stretching region is observed at ∼1703 cm⁻¹ which is attributed to the hydrogen bonding with methanol. A peculiar feature in this study is that upon dilution, the peak at ∼1718 cm⁻¹ shows a minimum at C = 0.6, but on further dilution it shows a blue shift. However, the other peak at ∼1711 cm⁻¹ shows a continuous red shift with dilution as well as a maximum at C = 0.7 in the linewidth vs. concentration plot, which is essentially due to competition between motional narrowing and diffusion phenomena. A significant amount of narrowing in the Raman band at ∼1718 cm⁻¹ can be understood in terms of caging effect of the reference molecule by the solvent molecules at high dilution. A density functional theoretic (DFT) calculation on optimized geometries and vibrational frequencies of two conformers of neat (C₂H₅)₂CO in C₂ ad C_2v forms and the complexes with one and two CH₃OH molecules with both the conformers was performed. The experimental results and theoretical calculations together indicate a co-existence of two conformers as well as hydrogen bonded complex with methanol in the binary mixture, [(C₂H₅)₂CO + CH₃OH] at intermediate concentrations.     

Performance of single-reference coupled-cluster methods for quasidegenerate problems: The H4 model

Summary Several coupled-cluster methods based on a single-determinantal reference function have been applied to the model system composed of four hydrogen atoms in a trapezoidal arrangement. For nondegenerate regions all methods with the exception of CCD provide results within 1 mhartree of the exact (FCI) value. For degenerate regions such an accuracy can be achieved with the inclusion of theT ₃ andT ₄ clusters, in an iterative and in a noniterative manner. We report results for CCSDT, CCSDTQ-1, CCSD+TQ*(CCSD), CCSD+Q(CCSDT) plus other methods. In particular, the ACP method which has been proposed to indirectly account forT ₄ terms is critically analyzed by including allT ₃ contributions.     

Two Ce(SO4)2·4H2O polymorphs: Crystal structure and thermal behavior

Syntheses, crystal structures and thermal behavior of two polymorphic forms of Ce(SO₄)₂·4H₂O are reported. The first modification, α-Ce(SO₄)₂·4H₂O (I), crystallizes in the orthorhombic space group Fddd, with a=5.6587(1), b=12.0469(2), c=26.7201(3) Å and Z=8. The second modification, β-Ce(SO₄)₂·4H₂O (II), crystallizes in the orthorhombic space group Pnma, with a=14.6019(2), b=11.0546(2), c=5.6340(1) Å and Z=4. In both structures, the cerium atoms have eight ligands: four water molecules and four sulfate groups. The mutual position of the ligands differs in (I) and (II), resulting in geometrical isomerism. Both these structures are built up by layers of Ce(H₂O)₄(SO₄)₂ held together by a hydrogen bonding network. The dehydration of Ce(SO₄)₂·4H₂O is a two step (I) and one step (II) process, respectively, forming Ce(SO₄)₂ in both cases. During the decomposition of the anhydrous form, Ce(SO₄)₂, into the final product CeO₂, intermediate xCeO₂·yCe(SO₄)₂ species are formed.     

Comparison of decomposition procedures for analysis of titanium dioxide using inductively coupled plasma optical emission spectrometry

The determination of impurities in titanium dioxide pigments, such as Al, Cd, Cr, Fe, Mn, P, Zn and Zr, is relevant because trace elements affect pigment properties. The critical step in the analysis of this pigment is the conversion of the solid sample to a representative solution. This study compared four acid decomposition procedures for TiO₂ for the determination of Al, P and trace impurities using inductively coupled plasma optical emission spectrometry. The decomposition procedures investigated involved acid digestion with: (i) (NH₄)₂SO₄/H₂SO₄; (ii) HF/H₂SO₄; (iii) H₃PO₄; and (iv) HCl/HNO₃/HF. This latter mixture was tested in a microwave-assisted procedure with closed vessels. Comparing the procedures using conventional conductive heating, the procedure using (NH₄)₂SO₄/H₂SO₄ was the most suitable for complete decomposition of TiO₂ samples, requiring approximately 30 min. Applying a paired t-test, it was shown that all strategies led to results in agreement at a 95% confidence level with those obtained using X-ray fluorescence. The accuracy for Cr, Fe, P and Zr was also checked using a certified reference material, and again all results were in agreement at a 95% confidence level. The performance of two ICP-OESs, one based on a mini-torch using a radial view configuration, and the other based on an axial view configuration, were compared. Both plasmas are intensely affected by matrix constituents. The mini-torch plasma is less able to cope with high amounts of solids; however this parameter also negatively affects the background level when using axial-viewed ICP-OES.     

Chromium doped γ-Al2O3 powders. Features of the electrical double layer and state of the surface species

γ-Al₂O₃ samples, both pure and Cr doped, were prepared by heating at 470°C sol–gel precursors obtained by using aluminum tri-sec-butoxide [Al(OC₄H₉)₃] as the starting compound. The samples were characterised for phase composition (X-ray diffraction) and surface area (BET). Electrochemical determinations of the double layer reactivity of the pure and doped oxides were performed both by surface charge and by electrokinetic sonic amplitude (ESA) determinations. The interfacial electrostatic response is discussed and analysed also with reference to the sample surface state obtained by X-ray photoelectron spectroscopy (XPS).     

Supramolecular aggregation in new crystals with nonlinear optical properties: 2-aminophenol-HClO4, 3-aminophenol-HClO4 and 4-aminophenol-HClO4

Three new hybrid crystals of 2-aminophenol-HClO₄ (2-AP-HClO₄, 1), 3-aminophenol-HClO₄ (3-AP-HClO₄, 2) and 4-aminophenol-HClO₄ (4-AP-HClO₄, 3) were obtained and their crystal structures determined. The 1 crystallises in centrosymmetric space group C2/c of monoclinic system while the other two (2 and 3) crystallise in the non-centro symmetric space group P2₁ and P2₁2₁2₁, respectively. The oppositely charged units of the crystals, i.e. positively charged 2-APH⁺, 3-APH⁺ and 4-APH⁺ and ClO₄⁻, interact via weak N⁺–HO and O–HO hydrogen bonds forming 3D-supramolecular network. Relative to KDP the SHG efficiencies are 0.62 for 2 and 0.33 for 3, measured at 1064 nm using the Kurtz–Perry method.