Solubility and stability of (NH4)2SO4 · H2O2 in aqueous solutions and change in some crystallographic parameters of (NH4)2SO4 precipitates

Stability of (NH₄)₂SO₄ · H₂O₂ aqueous solutions and some structural changes in ammonium sulfate in the course of its solvation and subsequent desolvation were studied.     

Thermal stability of In2(MoO4)3 and phase equilibria in the MoO3–In2O3 system

Thermal stability of a compound forming in a binary system MoO₃?CIn₂O₃ was investigated by DTA/TG, XRD and SEM methods in this study. For the first time, the diagram of phase equilibria established in the whole range of concentrations of this system's components has been constructed. The temperature and concentration ranges of the components of MoO₃?CIn₂O₃ system in which the compound In₂(MoO₄)₃ co-exists in solid state with MoO₃ or In₂O₃ or with the liquid were determined. The composition and melting point of the eutectic mixture consisting of In₂(MoO₄)₃ and MoO₃ were found.     

Thermal stability of the β″ phase in the ZrO2-Zr3N4 system

Annealing of ZrO₂ in a nitrogen atmosphere leads to a nitrogen containing phase called phase having a trigonally distorted fluorite structure with ordered anion vacancies. DTA/TG investigations indicated that the phase decomposes intom-ZrO₂ above 500C releasing nitrogen during the reaction with oxygen. Prevention of oxygen uptake by use of closed tantalum tubes instead of open platinum crucibles enabled the detection of a new reversible phase transition at 965C. The thermoanalytical results have been confirmed by high temperature-X-ray investigation.Dedicated to Professor Dr. Roger Blachnik on the occasion of his 60^th birthday     

Phase Equilibria in the System NH4Al(SO4)2–H2SO4–H2O

Equilibrium solubility curves of the ammonium aluminium sulphate in aqueous solutions of sulphuric acid have been calculated using checked literature data and our own measurements. The concentration of sulphuric acid ranged from 0 to 23 mass%, temperature range between 20 and 60°C has been extrapolated up to 75°C by means of a thermodynamically based correlation method. The solubility correlation as well as the hydration analysis implied a possible destructuralization of solutions at higher acid concentrations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and Structure of [Pd(NH3)4][cis-Pd(NH3)2(SO3)2][Pd(NH3)3(SO3)] · H2O

A new palladium compound [Pd(NH₃)₄][cis-Pd(NH₃)₂(SO₃)₂][Pd(NH₃)₃(SO₃)] · H₂O (I) was synthesized and its structure was studied by X-ray powder diffraction method. In the course of the synthesis, the initial trans-diamminesulfite anionic complex is transformed into the cis-configuration. Further heating in aqueous solution results in isomerization of a substance into a neutral complex [Pd(NH₃)₃(SO₃)]. Crystals I are triclinic: a = 10.3297(2) Å, b = 14.1062(3) Å, c = 6.8531(1) Å, = 101.36(0)°, = 92.74(0)°, = 92.71(0)°, space group P1¯. Structure I consists of the columns with alternating cis-[Pd(NH₃)₂(SO₃)₂]^2– and [Pd(NH₃)₃(SO₃)] complexes and [Pd(NH₃)₄]²⁺ ions between the columns.     

Fe(III) extraction equilibria in the system: Fe2(SO4)3(NH4)2SO4 vs primene JM-T sulfate-toluene

Distribution coefficients for Fe(III) have been determined in the liquid-liquid extraction system Primene JM-T-toluene vs aqueous ammonium sulfate (and sodium sulfate) as a function of sulfate, acid, Fe(III) and amine sulfate concentrations. A study of loading equilibria as a function of time for this system indicates that equilibrium was largely achieved in 1 hr although some changes, possibly in the nature of the extracted species, occur up to approx. 20 hr. Extraction isotherms show a slope of 1 at low loadings, indicating the same degree of self association in both organic and aqueous phases, while the amine sulfate/iron ratio appears to approach 2.5 ± 0.25 at saturation loading. Results obtained by varying the sulfate concentration matrix indicates the formation of an aqueous complex of ferric ammonium sulfate which depresses iron distribution to the organic phase. The degree of aggregation of the amine sulfate, derived from iron distribution coefficient dependence on amine sulfate concentration data, is shown to be approx. 10.     

Thermodynamic properties and phase transitions of Tutton salt (NH4)2Co(SO4)2·6H2O crystals

The thermodynamic properties and phase transitions of Tutton salt (NH₄)₂Co(SO₄)₂·6H₂O single crystals were investigated with TG, DSC, and NMR. The first mass loss occurs in the vicinity of 360?K (T _d), which is interpreted as the onset of partial thermal decomposition. Phase transitions were found at 384?K?=?T _C1, 415?K?=?T _C2, and 443?K?=?T _C3. The temperature dependence of the spin?Clattice relaxation time, T ₁, for the H nuclei undergoes slight changes near T _C1 and T _C2. These changes are associated with changes in the geometry of the arrangement of water and five SO₄ oxygens and with proton hopping or the breaking of hydrogen bonds.     

Mechanochemical synthesis and thermal stability of phases in the Y2O3–Yb2O3 system

Substitutional, continuous solid solution of the general formula Y_2–xYb_xO₃ was obtained from the mixture of Y₂O₃ and Yb₂O₃ oxides, for the first time by the mechanochemical method in a high-energy ball milling. The monophasic samples of nanocrystalline solid solution for x?>?0.00 and x?<?2.00 were examined by the methods: XRD, DTA, SEM, IR and UV–Vis–DR. As follows from the results, the solid solution crystallizes in cubic system and is isostructural with Y₂O₃ and Yb₂O₃. The solution is stable in the air atmosphere up to at least 900°C, and its decomposition temperature decreases with the increase in x, that is, with decreasing number of Yb³⁺ ions replacing Y³⁺ ions in the crystal lattice of Y₂O₃. The energy band gap estimated for the solid solution varies from?~?5.30 eV for x?=?0.50 to?~?4.90 eV for x?=?1.50, which means that it is an insulator.

     

Structure,synthesis, and thermal properties of trans-[Ru(NO)(NH3)4(SO4)]NO3·H2O

In treatment of trans-[Ru(NO)(NH₃)₄(OH)]Cl₂ with concentrated sulfuric acid on heating trans-[Ru(NO)(NH₃)₄(SO₄)](HSO₄)·H₂O (I) is obtained with a yield close to quantitative. In the interaction of the saturated solution of I with a saturated NaNO₃ solution a trans-[Ru(NO)(NH₃)₄(SO₄)]NO₃·H₂O (II) precipitate forms whose structure is determined by single crystal XRD: space group P2₁2₁2₁, a = 6.8406(3) Å, b = 12.6581(5) Å, c = 13.3291(5) Å. A monodentately coordinated sulfate ion is in the trans-position to the nitroso group. Compound II is characterized by IR spectroscopy, powder XRD, and diffuse reflectance spectroscopy. The process of its thermolysis is studied; by differential scanning calorimetry the thermal effect of the dehydration reaction occurring on heating to 120°C (ΔH = 58.9 ± 1.5 kJ/mol) is estimated. The final product of the thermolysis of II is a mixture of Ru and RuO₂.     

Temperature dependence of the substrate selectivity in the hydroxylation of alkylbenzenes in the H2O2−H2SO4 system

The substrate selectivity in the hydroxylation of methylbenzenes in the H₂O₂−H₂SO₄ (70 wt.%) system was studied at 15–55 °C. The activation entropy correlates with the basicity of the arenes, while the substrate selectivity and activation enthalpy correspond both with the basicity and ionization potentials of ArH. We concluded that the structure of the reaction transition state is intermediate between a charge transfer complex and σ-complex. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 39–43, January–February, 1999.     

The revised phase diagram of the Ca3(PO4)2–YPO4 system. The temperature and concentration range of solid-solution phase fields

A revised version of the Ca₃(PO₄)₂–YPO₄ phase diagram has been proposed on the basis of results obtained by thermal analysis (DTA/DSC/TG) and X-ray diffraction methods. A limited solid solution with the structure of β-Ca₃(PO₄)₂ exists in the system. At 1,100 °C the maximal concentration of YPO₄ in the solid solution is ~15 mass%. The solid-solution phase field exists in the temperature range upto ~1,380 °C. Two high-temperature solid solutions with the structure of α′ and α-Ca₃(PO₄)₂ form in system as well, however only the α phase can be obtained by quenching from high temperatures. The Ca₃Y(PO₄)₃ compound with the structure of eulytite forms in the Ca₃(PO₄)₂–YPO₄ system at temperatures exceeding 1,255 °C and does not show any polymorphic transition.     

Etude vibrationnelle de la phase II des hydrogénodisulfates de triammonium, (NH4)3H(SO4)2 et (ND4)3D(SO4)2

The i.r. and Raman spectra of room temperature phase (phase II) of (NH₄)₃H(SO₄)₂ and (ND₄)₃D(SO₄)₂ as polycrystalline samples and single crystals have been investigated between 4000 and 30 cm⁻¹. An assignment of internal and external modes is given in terms of group frequencies and symmetry types. This crystal contains non-centrosymmetric dimers (SO₄HSO₄)³⁻ where sulphate ions are associated by strong asymmetric OH … O hydrogen bonds; they are characterized by two strong Raman bands at 1078 and 966 cm⁻¹, and a νOH frequency at about 1250 cm⁻¹. The acidic proton is statistically disordered around the crystallographic symmetry centre while all of the NH⁺₄ ions show an important dynamical orientational disorder.     

Thermochemical investigations of the systems KCl−KBr−H2O,K2SO4−(NH4)2SO4−H2O and KNO3−NH4NO3−H2O at 298.15 K

For the equilibrium solid phases occurring in the systems: KCl?KBr?H₂O, K₂SO₄?(NH₄)₂SO₄?H₂O and KNO₃?NH₄NO₃?H₂O, the concentration dependencies of differential solution enthalpies, Δ_sol H ₂ for several crystallization paths, were measured. The limiting differential solution enthalpies, Δ_sol H ₂ ⁰ , were determined by extrapolation of the above dependencies to the ionic strength,I _m ⁰ , corresponding to the appropriate binary solutions. For KCl?KBr?H₂O system only, the clear dependence between Δ_sol H ₂ ⁰ andI _m ⁰ values was found and discussed.     

Kinetics, substrate selectivity and mechanisms of the first step in the oxidation of alkylbenzenes in the HVO3−H2SO4 system

The kinetics, kinetic isotope effects, and substrate selectivity were studied for the oxidation of alkylbenzenes in the HVO₃−H₂SO₄ system at 30°C. The reaction proceeds by an electrophilic substitution mechanism through a slow step involving formation of a charge transfer complex between the arene and VO ₂ ⁺ cation and is similar to nitration by the NO ₂ ⁺ cation. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 6, pp. 349–353, November–December, 1999.     

Study of the solubility of components in the system Mg(ClO3)2-2NH2C2H4OH · H3C6H5O7-H2O

The solubility of components in the system Mg(ClO₃)₂-2NH₂C₂H₄OH · H₃C₆H₅O₇-H₂O was studied from the complete freezing temperature ?59.4°C to 20.0°C. A polythermal solubility diagram was constructed, in which the crystallization fields were determined for ice, Mg(ClO₃)₂ · 16H₂O, Mg(ClO₃)₂ · 12H₂O, Mg(ClO₃)₂ · 6H₂O, 2NH₂C₂H₄OH · H₃C₆H₅O₇ · H₂O, 2NH₂C₂H₄OH · H₃C₆H₅O₇, and two new compounds, [(HOC(CH₂COOH)₂COO)₂Mg · 2H₂O] and [HOC(CH₂COO)₂MgCOOH · 2H₂O], which were identified by chemical and physicochemical analysis methods.     

Theoretical studies of the g factors and local structures of the Ni3+ centers in Na2Zn(SO4)2·4H2O and K2Zn(SO4)2·6H2O crystals

The local structures and the g factors g_i (i = x, y, z) for Ni³⁺ centers in Na₂Zn(SO₄)₂·4H₂O (DPPH) and K₂Zn(SO₄)₂·6H₂O (PHZS) crystals are theoretically studied by using the perturbation formulas of the g factors for a 3d⁷ ion with low spin (S = 1/2) in orthorhombically compressed octahedra. In these formulas, the contributions to g factors from both the spin-orbit coupling interactions of the central ion and ligands are taken into account, and the required crystal-field parameters are estimated from the superposition model and the local geometry of the systems. Based on the calculations, the Ni-O bonds are found to suffer the axial compression δz (or Δz) of about 0.111 Å (or 0.036 Å) along the z-axis for Ni³⁺ centers in DPPH (or PHZS) crystals. Meanwhile, the Ni-O bonds may experience additional planar bond length variation δx (≈0.015 Å) along x- and y-axes for the orthorhombic Ni³⁺ center in DPPH. The theoretical g factors agree well with the experimental data. The obtained local structural parameters for both Ni³⁺ centers are discussed.     

A theoretical investigation on the structures of (NH3)·(H2SO4)·(H2O)0-14 clusters

Ternary clusters (NH₃)·(H₂SO₄)·(H₂O)_n have been widely studied. However, the structures and binding energies of relatively larger cluster (n > 6) remain unclear, which hinders the study of other interesting properties. Ternary clusters of (NH₃)·(H₂SO₄)·(H₂O)_n, n = 0-14, were investigated using MD simulations and quantum chemical calculations. For n = 1, a proton was transferred from H₂SO₄ to NH₃. For n = 10, both protons of H₂SO₄ were transferred to NH₃ and H₂O, respectively. The NH₄⁺ and HSO₄⁻ formed a contact ion-pair [NH₄⁺-HSO₄⁻] for n = 1-6 and a solvent separated ion-pair [NH₄⁺-H₂O-HSO₄⁻] for n = 7-9. Therefore, we observed two obvious transitions from neutral to single protonation (from H₂SO₄ to NH₃) to double protonation (from H₂SO₄ to NH₃ and H₂O) with increasing n. In general, the structures with single protonation and solvated ion-pair were higher in entropy than those with double protonation and contact ion-pair of single protonation and were thus preferred at higher temperature. As a result, the inversion between single and double protonated clusters was postponed until n = 12 according to the average binding Gibbs free energy at the normal condition. These results can serve as a good start point for studies of the other properties of these clusters and as a model for the solvation of the [H₂SO₄-NH₃] complex in bulk water.     

Crystal growth, structural, thermal, and dielectric characterization of Tutton salt (NH4)2Fe(SO4)2·6H2O crystals

A good quality single crystal of Tutton salt, (NH₄)₂Fe(SO₄)₂·6H₂O, with dimensions 6 × 7 × 3 mm³ was successfully grown by the slow evaporation growth technique at ambient temperature. The grown crystal was subjected to single crystal X-ray diffraction study which confirms that the grown crystal is monoclinic in nature with the space group P2₁/c. Optical absorption spectrum reveals that the grown crystal has good optical transparency in the entire visible region and its energy band gap was determined. The thermal behavior of the grown crystal was investigated by thermogravimetric and differential thermal analysis. The dielectric measurements were carried out to determine the dielectric behavior of the crystal.     

A theoretical study of the H2SO4+H2O → HSO4 −+H3O+ reaction at the surface of aqueous aerosols

The surface region of sulfate aerosols (supercooled aqueous concentrated sulfuric acid solutions) is the likely site of a number of important heterogeneous reactions in various locations in the atmosphere, but the surface region ionic composition is not known. As a first step in exploring this issue, the first acid ionization reaction for sulfuric acid, H₂SO₄ + H₂O HSO₄^– + H₃O⁺, is studied via electronic structure calculations at the Hartree–Fock level on an H₂SO₄ molecule embedded in the surface region of a cluster containing 33 water molecules. An initial H₂SO₄ configuration is selected which could produce H₃O⁺ readily available for heterogeneous reactions, but which involves reduced solvation and is consistent with no dangling OH bonds for H₂SO₄. It is found that at 0 K and with zero-point energy included, the proton transfer is endothermic by 3.4 kcal/mol. This result is discussed in the context of reactions on sulfate aerosol surfaces and, further, more complex calculations.Contribution to the Jacopo Tomasi Honorary Issue