Structure of aqueous dispersions of Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes

Behavior of hydrosilicate nanotubes of composition Mg₃Si₂O₅(OH)₄ in aqueous dispersions was studied. Experiments devoted to observation of steady-state and relaxation electro-optical effects demonstrated that, irrespective of their initial concentration in water, nanotubes form stable bulk aggregates with weak anisotropy, rather than a homogeneous system of separate suspended nanosize cylinders.     

Synthesis and study of sodium triuranate Na<Subscript>2</Subscript>(UO<Subscript>2</Subscript>)<Subscript>3</Subscript>O<Subscript>3</Subscript>(OH)<Subscript>2</Subscript>

Sodium triuranate Na₂(UO₂)₃O₃(OH)₂ was synthesized by the reaction between aqueous uranyl acetate solution and aqueous sodium nitrate solution under hydrothermal conditions at 200°C. The composition and structure of the synthesized compound were determined, and its dehydration and thermal decomposition were studied, by chemical analysis, X-ray diffraction, IR spectroscopy, and thermal analysis.     

Synthesis,characterization and very strong luminescence of a new 3 D europium sulfate Eu<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript>

A new 3 D europium sulfate Eu₂(H₂O)₄(SO₄)₃ 1 is synthesized solvothermally and characterized by single crystal X-ray diffraction, IR spectrum, TG, powder XRD, and ultraviolet excitation and emission spectrum. This compound crystallizes in the triclinic system with the space group P-1, a = 6.7520(9) Å, b = 9.1077(12) Å, c = 10.5910(14) Å, α = 94.432(2)°, β = 107.1170(10)°, γ = 99.160(2)°, V = 609.17(14) ų, Z = 2. The open framework of the title compound is an eight-membered ring channel along the crystallographic a-axis, which is built up by EuO₈ polyhedra and SO₄ tetrahedra.     

New uranyl complex with imidazolidine-2-one [UO<Subscript>2</Subscript>(Imon)<Subscript>4</Subscript>(H<Subscript>2</Subscript>O)](ClO<Subscript>4</Subscript>)<Subscript>2</Subscript>: Structure and some properties

A complex of uranyl perchlorate with imidazolidine-2-one as the molecular ligand, [UO₂(Imon)₄(H₂O)](ClO₄)₂ (I), was synthesized and structurally characterized by X-ray diffraction analysis. The coordination number of the uranium atom is 7. The nearest environment of the uranyl ion includes four O atoms of the imidazolidine-2-one molecules and one O atom of the water molecule. The perchlorate anions are outer-sphere ligands. The crystals are monoclinic: space group P2₁/c; a = 16.294(3) Å, b = 16.135(3) Å, c = 9.987(2) Å, = 97.69 (3)°, V = 2603.0 (9) ų, (calcd) = 2.117 g/cm³, Z = 4. The IR and luminescence spectra of the complex were recorded.Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 12, 2004, pp. 919–924.Original Russian Text Copyright © 2004 by Andreev, Antipin, Budantseva, Tuchina, Serezhkina, Fedoseev, Yusov.     

Glass formation in the CaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> and SrO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> systems

A physicochemical study of glasses based on the MO-Bi₂O₃-B₂O₃ and SrO-Bi₂O₃-B₂O₃ systems was performed. Glass formation regions were found. The structural and optical properties, as well as the thermal behavior of the glasses, were studied.     

Comparison of the Solubility of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> in High Temperature Water

As the solubility is a direct measure of stability, this study compares the solubilities of ZnFe₂O₄, Fe₃O₄ and Fe₂O₃ in high temperature water. Through literature analysis and formula derivation, it is shown that it is reasonable to assume ZnFe₂O₄ and Fe(OH)₃ coexist when ZnFe₂O₄ is dissolved in water. Results indicated that the solubility of ZnFe₂O₄ is much lower than that of Fe₂O₃ or Fe₃O₄. The low solubility of ZnFe₂O₄ indicates that it is more protectively stable as an anticorrosion phase. Moreover, the gap between the solubility of ZnFe₂O₄ and that of Fe₃O₄ or Fe₂O₃ was enlarged with an increase of temperature. This means that ZnFe₂O₄ is more protective at higher temperatures. Further analysis indicated that with the increase of temperature, the solubility of ZnFe₂O₄ changed little while those of Fe₂O₃ or Fe₃O₄ changed a lot. Little change of the solubility of ZnFe₂O₄ with increase of temperature showed that ZnFe₂O₄ is stable. The very low and constant solubility of ZnFe₂O₄ suggests that it is more protective than Fe₂O₃ and Fe₃O₄, especially in water at higher temperature.     

Kinetics of phase formation upon the treatment of La<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript> and La<Subscript>2</Subscript>O<Subscript>2</Subscript>SO<Subscript>4</Subscript> in a hydrogen flow

The sequence of phases occurring during treatment of lanthanum sulfate, La₂(SO₄)₃ and lanthanum oxysulfate, La₂O₂SO₄ in a hydrogen flow is established. The temperature ranges in which homogeneous La₂O₂S is produced are revealed: when La₂(SO₄)₃ is a precursor, the range is 770–1220 K; in the case of La₂O₂SO₄, the interval is 950–1220 K. The kinetic curves showing the time dependence of the yield of La₂O₂S is constructed and treated using the Avrami-Erofeev and contracting volume equations. The activation energies of the reactions are determined.     

Dissymmetrization of crystal structures of grossular-andradite garnets Ca<Subscript>3</Subscript>(Al,Fe)<Subscript>2</Subscript>(SiO<Subscript>4</Subscript>)<Subscript>3</Subscript>

The crystal structures of three birefringent grossular-andradite natural garnets Ca₃(Al,Fe)₂(SiO₄)₃ were investigated using single-crystal X-ray diffraction data (MoK_α, number of reflections measured 8065, 10619, 9213; R = 2.81, 2.74, 3.26%). According to the values of unit cell constants, inconsistent intensities of reflections and appearance of additional (forbidden) reflections explored garnets have different symmetry: cubic, sp. gr. (Fe/(Fe + Al) = 0.078, Δn = 0.0002); orthorhombic, sp. gr. Fddd (Fe/(Fe + Al) = 0.58, Δn = 0.0089); triclinic, sp. gr. or I1 and pseudo-orthorhombic (Fe/(Fe + Al) = 0.23, Δn = 0.0066). Careful refinement of all crystal structures in space groups , Fddd and has confirmed the symmetry reduction detected on the diffraction patterns and shown that dissymmetrization of cubic garnets connects with partial ordering of trivalent cations over Y-sites. Direct linear relationship between Fe-occupancy, an average Y–O bond lengths and octahedral O–O edges has been revealed. Cluster models of dissymmetrization have been regarded. Evidence for the “growth dissymmetrization” phenomena (kinetic phase transformations) as the reasons of the symmetry reduction of cubic garnets has been discussed. The reasonable assumption that the garnets crystal structures described as orthorhombic are triclinic, but the deviations from the orthorhombic symmetry so small, that cannot be manifested by of X-ray diffraction study has been taken.     

Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> phase diagram

Phase relations in the Y₂O₃-Ga₂O₃ system were studied by the anneal-and-quench technique in air within 1000–2300°C, and a phase diagram was plotted. Three compounds were found to form: Y₃GaO₆, Y₄Ga₂O₉, and Y₃Ga₅O₁₂; the temperature and concentration bounds of stability were determined for these compounds. Indexing results for Y₃GaO₆ are given.     

Palladium clusters Pd<Subscript>4</Subscript>(SR)<Subscript>4</Subscript>(OAc)<Subscript>4</Subscript> and Pd<Subscript>6</Subscript>(SR)<Subscript>12</Subscript> (R = Bu,Ph): Structure and properties

The structures of the Pd₄(SBu)₄(OAc)₄ (I) and Pd₆ (SBu)₁₂ (II) palladium clusters are determined by the X-ray diffraction method. For cluster I: a = 8.650(2), b = 12.314(2), c = 17.659(4) Å, α = 78.03(3)°, β = 86.71(2)°, γ = 78.13(3)°, V = 1800.8(7) ų, ρcalcd = 1.878 g/cm³, space group P \(\bar 1\), Z = 4, N = 3403, R = 0.0468; for structure II: a = 10.748(2), b = 12.840(3), c = 15.233(3) Å, α = 65.31(3)°, β = 70.10(3)°, γ = 72.91(3)°, V = 1767.4(6) ų, ρ calcd = 1.605 g/cm³, space group P \(\bar 1\), Z = 1, N = 3498, R = 0.0729. In cluster I, four Pd atoms form a planar cycle. The neighboring Pd atoms are bound by two acetate or two mercaptide bridges (Pd…Pd 2.95–3.23 Å, Pd…Pd angles 87.15°–92.85°). In cluster II, the Pd atoms form a planar six-membered cycle with Pd···Pd distances of 3.09–3.14 Å, the PdPdPd angles being 118.95°–120.80°. The Pd atoms are linked in pairs by two mercaptide bridges. The formation of clusters I and II in solution is proved by IR spectroscopy and calorimetry. Analogous clusters are formed in solution upon the reaction of palladium(II) diacetate with thiophenol.     

The synthesis and thermochemical study of (Mg,Fe)<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes

Nanotubular (Mg,Fe²⁺,Fe³⁺)₃Si₂O₅(OH)₄ hydrosilicates with a chrysotile structure were synthesized under hydrothermal conditions. The phases prepared were studied thermochemically on a high-temperature Tian-Calvet microcalorimeter by solution calorimetry. The standard enthalpies of formation of magnesium-iron nanotubular hydrosilicates were determined. The formation of iron-containing nanotubes was shown to be lass favorable energetically than the formation of magnesium nanotubes.     

Mechanism of the initiation of combustion in CH<Subscript>4</Subscript>(C<Subscript>2</Subscript>H<Subscript>2</Subscript>)/Air/O<Subscript>3</Subscript> mixtures by laser excitation of the O<Subscript>3</Subscript> molecules

The possibility of enhancing the ignition and combustion of the CH₄/air/O₃ and C₂H₂/air/O₃ mixtures by exciting the asymmetric vibrations of the O₃ molecule with CO₂ laser radiation is considered. Even the admixture of small amounts of O₃ (2.5–5.0 vol %) into the hydrocarbon/air mixtures intensifies ignition and shortens the induction period. The excitation of the O₃ molecules with 9.7-μm radiation speeds up the chain process and further reduces the induction period and the ignition temperature. The induction period can be shortened by a factor of 10–100 even at low radiation energies absorbed by the gas (E _S = 10^?3-10^?2 J/cm³).     

Thermal synthesis of the (Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>1–x</Subscript>(Er<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>x</Subscript> pigments

The synthesis of new compounds based on Bi₂O₃ is investigated because they can be used as new environmentally friendly inorganic pigments. Chemical compounds of the (Bi₂O₃)_1–x(Er₂O₃)_x type were synthetized. The host lattice of these pigments is Bi2O3 that is doped by Er³⁺ ions. The incorporation of doped ions provides interesting colours and contributes to an increase in the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments.     

Synthesis,structural, spectral,thermal and comparative biological activity studies of [V<Subscript>2</Subscript>O<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>]

The hydrothermal reaction of a mixture of V₂O₅, VCl₃, 2,5-pyridinedicarboxylic acid and diluted H₂SO₄ for 68 h at 180°C gives a blue colored solution which yields prismatic blue crystals of IV ₂ ^IV O₂(SO₄)₂(H₂O)₆] (1) in 32% yield (based on V). Complex 1 was investigated by means of elemental analysis (C, H and S), TGA, FT-IR, manganometric titration, Single Crystal X-ray Diffraction Methods and also comparative antimicrobial activities. Crystal data for the compound: monoclinic space group P2₁/c and unit cell parameters are a = 7.3850(12) Å, b = 7.3990(7) Å, c = 12.229(2) Å, β = 108.976(12)° and Z = 2. Although structure of 1 as a natural mineral has been previously determined, this work covers new preparation method and full characterization of 1 along with comparison of antibacterial activity between 1 and the commercial vanadium(IV) oxide sulfate hydrate compounds, VOSO₄ · xH₂O (Riedel-de Haën and Alfa Aesar brand names). 1 was evaluated for the antimicrobial activity against gram-positive, gram-negative bacteria, yeasts and mould compared with the commercial VOSO₄ · xH₂O compounds. 1 showed weak activity against bacteria Bacillus cereus, Nocardia asteroides and yeast Candida albicans. A good antimicrobial activity was recorded against Cirtobacter freundii (15 mm). There are only a few reproducible well-defined vanadium(IV) starting materials to use for exploring the synthesis of new materials. VCl₄, VO(acac)₂, VOSO₄ · xH₂O and [V(IV)OSO₄(H₂O)₄] · SO₄ · [H₂N(C₂H₄)₂NH₂] are common starting materials for such applications. In addition to these compounds, 1 can be used as an oxovanadium precursor.     

Synthesis,crystal structure,and biological properties of the complex [Co(DmgH)<Subscript>2</Subscript>(Seu)<Subscript>1.4</Subscript>(Se-Seu)<Subscript>0.5</Subscript>(Se<Subscript>2</Subscript>)<Subscript>0.1</Subscript>][BF<Subscript>4</Subscript>]

A new Co(III) dioxime complex with selenocarbamide was obtained by the reaction of Co(BF₄)₂ ? 6H₂O, DmgH₂, and Seu (DmgH2 = dimethylglyoxime, Seu = selenocarbamide). According to X-ray diffraction (CIF file CCDC no. 1485732), the product was an ionic coordination compound with unusual composition, [Co(DmgH)₂(Seu)_1.4(Se-Seu)_0.5(Se₂)_0.1][BF₄] (I). Apart from two monodeprotonated DmgH￣ molecules, the central atom coordinates neutral Seu, Se-Seu, and Se₂ molecules. Thus, the crystal contains the complex cations [Co(DmgH)₂(Seu)₂]⁺, [Co(DmgH)₂(Seu)(Se-Seu)]⁺, and [Co(DmgH)₂(Seu)(Se₂)]⁺. Each [BF₄]￣ anion is linked to the cations not only by electrostatic forces but also by intermolecular N–H···F hydrogen bonds (H-bonds). The complex cations are combined by intermolecular N–H···O H-bonds. The new coordination compound was found to possess biological activity. Treatment of the garlic (Allium sativum L.) foliage with an aqueous solution of I optimizes the content of selenium in the leaves and cloves and enhances the growth and plant productivity. The organs of treated plants are characterized by enhanced antioxidant protection owing to increasing activity of antioxidant enzymes and contents of proline and assimilation pigments, and decreasing lipid peroxidation.     

Synthesis and structure of [UO<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>){CONH<Subscript>2</Subscript>N(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>}<Subscript>2</Subscript>]

The single crystals of [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] were synthesized and studied by X-ray diffraction. The crystals are monoclinic, a = 7.461(2) Å, b = 8.828(2) Å, c = 11.756(2) Å, β = 107.21(3)°, space group Pc, Z = 2, R = 2.94%. The structure comprises infinite chains [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] extended along [001] and corresponding to the AT¹¹M ₂ ¹ crystallochemical group (A = UO ₂ ²⁺ , T¹¹ = C₂O ₄ ^2? , M¹ = N,N-CONH₂N(CH₃)₂) of uranyl complexes. The chains are connected into a three-dimensional framework by hydrogen bonds involving the oxygen atoms of oxalate and uranyl ions and the N,N-dimethylcarbamide methyl groups.     

Promoted porous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia decomposition

Transition metal catalysts have been considerably used for NH₃ decomposition because of the potential application in CO_x-free H₂ generation for fuel cells. However, most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components. Here, we adopted an efficient method, aerosol-assisted self-assembly approach (AASA), to prepare the optimized cobalt-alumina (Co₃O₄-Al₂O₃) catalysts. The Co₃O₄-Al₂O₃ catalysts exhibited excellent catalytic performance in the NH3 decomposition reaction, which can reach 100% conversion at 600 °C and maintain stable for 72 h at a gaseous hourly space velocity (GHSV) of 18000 cm³ g_cat^?1 h^?1. The catalysts were characterized by various techniques including transmission electron microscope (TEM), scanning electron microscope (SEM), nitrogen sorption, temperature-programmed reduction by hydrogen (H₂-TPR), ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction (XRD) to obtain the information about the structure and property of the catalysts. H₂-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species, which influences the redox properties of the catalysts. It is found that even a low content of alumina (10 at%) is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components, which ensures the high activity and superior stability of the cobalt-alumina catalysts.     

Synthesis,structure, and properties of V<Subscript>2</Subscript>O<Subscript>3</Subscript>(XO<Subscript>4</Subscript>)<Subscript>2</Subscript> (X = S,Se)

Compounds described as V₂O₃(XO₄)₂, where X = S or Se, were prepared from vanadium(V) oxide mixtures with concentrated sulfuric and selenic acids. The physicochemical properties of the products were studied; for V₂O₃(SeO₄)₂, the crystal structure was determined by powder X-ray diffraction and neutron diffraction, and its key differences from the structure of V₂O₃(SO₄)₂ were identified. V₂O₃(SeO₄)₂ crystallizes in the monoclinic system with the unit cell parameters a = 15.3831(2)Å, b = 5.54096(5)Å, c = 9.71644(7)Å, β = 111.886(1)°, V = 768.51ų, space group C2/c (no. 15).     

Antiferromagnetic coupling in [Mn<Subscript>12</Subscript>O<Subscript>12</Subscript>(O<Subscript>2</Subscript>CMe)<Subscript>6</Subscript>(<Emphasis Type="Italic">p</Emphasis>-CO<Subscript>2</Subscript>-phenyl nitronyl

The synthesis of [Mn₁₂O₁₂(O₂CMe)₆(p-CO₂-phenyl nitronyl nitroxide)₁₀(H₂O)₄]· 4H₂O, (1), by direct replacement of some of the acetate groups in [Mn₁₂O₁₂(O₂CMe)₁₆(H₂O)₄] · 4H₂O · 2MeCO₂H, (2), with the organic radical p-HO₂C-phenyl nitronyl nitroxide, (3), is reported. E.p.r. spectra show exchange narrowing in (1) due to coupling between the manganese ions and radicals. The isotropic hyperfine splitting constant from the manganese ions is a = 96 Oe at 5.5K. The magnetic susceptibility indicates antiferromagnetic exchange interactions between the manganese ions and the radicals with the Weiss constant = -25 K. The spin was determined to be S = 6 from magnetization data in the 2--30 K temperature range at 50 kOe, suggesting a mixture of ground state with excited states.     

Synthesis and crystal structure of a Cu(II) complex Cu<Subscript>2</Subscript>(Endc)<Subscript>2</Subscript>(Bipy)<Subscript>2</Subscript> and its photoluminescence properties

A novel Cu(II) complex Cu₂(Endc)₂(Bipy)₂ has been synthesized by the reaction of Cu(NO₃)₂ · 3H₂O, Endc (endo-norbornene-cis-5,6-dicarboxylic acid), and Bipy (2,2-bipyridine) at room temperature. Elemental analysis, IR spectra, and X-ray single-crystal diffraction were carried out to determine the composition and crystal structure. Crystal data for this complex: triclinic, P \(\bar 1\) with a = 9.0373(10), b = 10.1637(11), c = 10.5574(12) Å, α = 65.78(1)°, β = 72.32(2)°, β = 73.23(2)°, Z = 1, V = 827.46(16) ų, ρ _c = 2.160 g/cm³, F(000) = 410.0, R = 0.0483 and wR = 0.0958 independent reflections for 4468 observed ones (I > 2 σ(I)).The Cu²⁺ ion is coordinated by two nitrogen atoms from the Bipy molecule and three oxygen atoms from two Endc, giving a distorted squarepyramidal coordination geometry. Two neighboring Cu²⁺ ions are bridged by a pair of bimonodentate carboxyl groups of different Endc acids, giving a centrosymmetrical binuclear structure which a Cu…Cu distance of 3.2946 Å. The photoluminescence properties of the complex were studied at room temperature. The complex displays an obvious photoluminescent emission upon excitation at 390 nm in the solid state.