Alkalisalze eines neuen Vanadat(IV,V)-Ions

Zusammenfassung Durch homogene Acidifizierung von NH₄-, Na- bzw. K-Thiovanadatlösungen wurden die Salze (NH₄)₂V₃O₈·1/2 H₂O, Na₃V₅O₁₂·8 H₂O und K₃V₅O₁₂·5 H₂O kristallin hergestellt. Die beiden letzteren lassen sich als Dekavanadate(IV, V) mit dem Anion [V₈ ^IVV₂ ^VO₂₄]^6– formulieren und bilden so weitere Glieder einer schon bekannten Reihe entsprechender Anionen mit dem V^IVV^V-Verhältnis 28 bis 73.

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Homogeneous acidification of solutions of NH₄-, Na-, or K-thiovanadates yield the crystalline salts (NH₄)₂V₃O₈·1/2 H₂O, Na₃V₅O₁₂·8 H₂O and K₃V₅O₁₂·5 H₂O. The latter two can be formulated as decavanadates(IV,V), containing the anion [V₈ ^IVV₂ ^VO₂₄]^6– and constituting new members of a series of already known anions with ratios of V^IVV^V from 28 to 73.

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Mit 1 Abbildung

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6. Mitt.:E. Hayek undU. Pallasser, Mh. Chem.99, 2126 (1968).     

Kryometrische Untersuchungen. IV. Lösungen von oxidischen Mo6+- und Cr6+-Verbindungen in geschmolzenem K2Cr2O7 und KNO3

The depression of freezing point of molten K₂Cr₂O₇ and KNO₃ as solvents was measured after addition of small concentrations of the following compounds: to K₂Cr₂O₇: MoO₃, CrO₃, (NH₄)₂CrO₄, K₂MoO₄, Na₂MoO₄, Li₂MoO₄, and Na₂Mo₂O₇, respectively; to KNO₃: CrO₃, (NH₄)₂Cr₂O₇ K₂Cr₂O₇, K₂CrO₄ and MoO₃, (NH₄)₆(Mo₇O₂₄) · 4 H₂O, K₂Mo₂O₇, K₂MoO₄, Na₂MoO₄ and Li₂MoO₄, respectively. It could be concluded from the measured values of the freezing point depression if a reaction between solvent and solute took place.     

Dehydrative cyclization of serine, threonine, and cysteine residues catalyzed by molybdenum(VI) oxo compounds

Commercially available molybdenum(VI) oxides such as (NH₄)₂MoO₄, (NH₄)₆Mo₇O₂₄·4H₂O, MoO₂(acac)₂, and MoO₂(TMHD)₂ are highly effective dehydrative cyclization catalysts for the synthesis of a variety of oxazolines. The reaction proceeds with a complete retention of configuration at the β-position. For the dehydrative cyclization of cysteine derivatives, bis(2-ethyl-8-quinolinolato)dioxomolybdenum(VI) shows remarkable catalytic activity and gives thiazolines without a significant loss of stereochemical integrity at the C2-exomethine positions.     

Thermal behavior of the polyoxometalates derived from H3PMo12O40 and H4PVMo11O40

The aim of this study is to investigate the influence of some monovalent counter-ions (NH₄ ⁺, K⁺ and Cs⁺) on thermal behavior of polyoxometalates derived from H₃PMo₁₂O₄₀ (HPM) and H₄PVMo₁₁O₄₀ (HPVM) by replacing the protons. The IR and UV-VIS-DRS spectra of some acid and neutral NH₄ ⁺, K⁺, Cs⁺ salts, which derived from HPM and HPVM, confirmed the preservation of Keggin units (KU) structure. The X-ray diffraction spectra clearly showed the presence of a cubic structure. The non-isothermal decomposition of studied polyoxometalates proceeds by a series of processes: the loss of crystallization water; the loss of O₂ accompanying with a reduction of V⁵⁺→V⁴⁺ and Mo⁶⁺→Mo⁵⁺; the loss of constitution water started at 360°C for HPVM salts and 420°C for HPM salts; the decomposition of ammonium ion over 420°C with NH₃, N² and H₂O elimination and simultaneous processes of reduction (V⁵⁺→ V⁴⁺ and Mo⁶⁺→ Mo⁵⁺ or Mo⁴⁺) associating with endothermic effects; reoxidation of Mo⁵⁺, Mo⁴⁺ and V⁴⁺with a strong exothermic effect; destruction of KU to the oxides: P₂O₅, MoO₃ and V₂O₅ and the crystallization of MoO₃. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mössbauer,FT-IR,and XRD study on the crystallization of highly functional tungstate and vanadate glasses

⁵⁷Fe-Mössbauer spectra of 38Na₂O·61WO₃·⁵⁷Fe₂O₃ glasses, heat treated at 355°C for 5–150 min, show a change of the coordination number of Fe³⁺ from 6 (FeO₆ octahedra) to 4 (FeO₄ tetrahedra), as a result of the formation of Na₂W₂O₇ (Na₂O/WO₃=1/2), Na₂WO₄ (Na₂O/WO₃=1.0), FeWO₄, and Fe₂WO₆ phases.⁵⁷Fe-Mössbauer spectra of 25K₂O·65V₂O₃·10Fe₂O₃ glasses show a drastic decrease of and after the heat treatment at 340°C for 10–2100 min, since a homogeneous crystallization took place without a phase separation. A KV₃O₈ phase with the K₂O/V₂O₅ ratio of 1/3 was precipitated, and the ratio was equal to the K₂O/(V₂O₅+Fe₂O₃) ratio of the original 25K₂O·65V₂O₃·10Fe₂O₃ glass.     

Cryoscopic studies in molten salts. Dissociation state of some alkali isopolymolybdates and some related molybdenum(VI) compounds in molten K2Cr2O7and KNO3

The dissociation state of the solutes M₂MoO₄, M₂Mo₃O₁₀, M₂Mo₄O₁₃, M₂Mo₅O₁₆ (MRb or Cs), Na₂CrO₄·MoO₃, K₂CrO₄·2 MoO₃, Cr₂Mo₃O₁₂ and V₂MoO₈ was studied cryoscopically in molten K₂ Cr₂O₇ and KNO₃ solvents. The freezing point depression, ΔT, of the solvents was obtained by measuring the cooling curves of the binary salt mixtures over unlimited range of solute concentration. The number of foreign ions obtained ν, showed that the solutes were either simply dissociated in the melt into the probable stable species (MoO₄)^2?, (Mo₃O₁₀)^2?, (Mo₄O₁₃)^2? and (Mo₅O₁₆)^2? or, in some cases after reactions and rearrangements, into (CrMo₂O₁₀)^2? heteropolyions. The solute V₂MoO₈, on the other hand, was found to dissolve without any apparent dissociation. An agreement between the experimental and calculated values of activity, a, based on the Temkin and Random Mixing models and that of Van't Hoff's equation support the proposed simple dissocia- tion scheme for K₂Cr₂O₇Cs₂MoO₄ system.     

Tetraalkylammonium fluorooxoperoxovanadates

Summary Compounds crystallizing from theMOH-HF-V₂O₅-H₂O₂-H₂O (M=N(CH₃)₄, N(C₂H₅)₄, N(C₄H₉)₄) system have been characterized by elemental analysis, vibrational spectra, and X-ray powder patterns. Besides [N(CH₃)₄]₂[VO(O₂)₂F]·2H₂O (1) and [N(CH₃)₄]₃[V₂O₂(O₂)₄F] (2) which correspond to the known compoundsM ₂[VO(O₂)₂F] (M=K, NH₄, Cs) and (NH₄)₃[V₂O₂(O₂)₄F]·2H₂O, respectively, complexes of two new types have been obtained: [N(C₂H₅)₄]₂[V₂O_5–x (O₂) _x F₂]·H₂O(x0.25,3) and the first trinuclear peroxo complex of vanadium(V), [N(C₄H₉)₄]₂[V₃O₃(O₂)₄F₃]·6H₂O(4).

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Tetraalkylammonium-Fluorooxoperoxovanadate

Zusammenfassung Aus dem SystemMOH-HF-V₂O₅-H₂O₂-H₂O (M=N(CH₃)₄), N(C₂H₅)₄, N(C₄H₉)₄) kristallisierende Verbindungen wurden mittels Elementaranalyse, Schwingungsspektroskopie und Röntgendiffraktion charakterisiert. Neben [N(CH₃)₄]₂[VO(O₂)₂F]·2H₂O (1) und [N(CH₃)₄]₃][V₂O₂(O₂)₄F] (2), welche den bekannten VerbindungenM ₂[VO(O₂)₂F] (M=K, NH₄, Cs) und (NH₄)₃[V₂O₂(O₂)₄)F]·2H₂O entsprechen, wurden zwei neue Typen von Komplexen erhalten: [N(C₂H₅)₄]₂[V₂O_5–x (O₂) _x F₂]·H₂O (x0.25,3) und der erste dreikernige Peroxokomplex von Vanadium(V), [N(C₄H₉)₄]₂[V₃O₃(O₂)₄F₃]·6H₂O (4).

     

Crystal structure and magnetic properties of Li,Cr-containing molybdates Li3Cr(MoO4)3, LiCr(MoO4)2 and Li1.8Cr1.2(MoO4)3

Single crystals of LiCr(MoO₄)₂, Li₃Cr(MoO₄)₃ and Li_1.8Cr_1.2(MoO₄)₃ were grown by a flux method during the phase study of the Li₂MoO₄-Cr₂(MoO₄)₃ system at 1023 K. LiCr(MoO₄)₂ and Li₃Cr(MoO₄)₃ single phases were synthesized by solid-state reactions. Li₃Cr(MoO₄)₃ adopts the same structure type as Li₃In(MoO₄)₃ despite the difference in ionic radii of Cr³⁺ and In³⁺ for octahedral coordination. Li₃Cr(MoO₄)₃ is paramagnetic down to 7 K and shows a weak ferromagnetic component below this temperature. LiCr(MoO₄)₂ is isostructural with LiAl(MoO₄)₂ and orders antiferromagnetically below 20 K. The magnetic structure of LiCr(MoO₄)₂ was determined from low-temperature neutron diffraction and is based on the propagation vektor . The ordered magnetic moments were refined to 2.3(1) μ_B per Cr-ion with an easy axis close to the [1 1 1¯] direction. A magnetic moment of 4.37(3) μ_B per Cr-ion was calculated from the Curie constant for the paramagnetic region.The crystal structures of the hitherto unknown Li_1.8Cr_1.2(MoO₄)₃ and LiCr(MoO₄)₂ are compared and reveal a high degree of similarity: In both structures MoO₄-tetrahedra are isolated from each other and connected with CrO₆ and LiO₅ via corners. In both modifications there are Cr₂O₁₀ fragments of edge-sharing CrO₆-octahedra.     

Tripotassium trichromium (III) tetraarsenate K3Cr3(ASO4)4: synthesis, structural study, IR spectroscopy characterization and ionic behavior

The potassium chromium (III) arsenate K₃Cr₃(AsO₄)₄ is prepared by solid state reaction at 900°C from a mixture of K₂CO₃, As₂O₃ and (NH₄)₂Cr₂O₇. It is structurally characterized by single-crystal X-ray diffraction. It crystallizes in the Cmca (no. 64) space group with a=10.671(1) Å, b=20.911(5) Å, c=6.500(3) Å, V=1450.4(8) Å³, Z=4, R(F²)=0.0424 and Rω(F²)=0.1199 for 846 reflections with F²>2σ(F²). The structure consists of CrO₆ octahedra and AsO₄ tetrahedra sharing corners and edges to form a two-dimensional framework. The K⁺(2) cations are located in the interlayer space. Conductivity measurement () shows that K₃Cr₃(AsO₄)₄ is a poor ionic conductor.     

The thermal decomposition of (NH4)[VO(O2)2(NH3)]

The compound, (NH₄)[VO(O₂)₂(NH₃)], thermally decomposes to ammonium metavanadate, which then decomposes to vanadium pentoxide. Using a heating rate of 5 deg·min^–1, the first decomposition step occurs between 74° and 102°C. The transformation degree dependence of the activation energy (-E) is shown to follow a decreasing convex form, indicating that the first decomposition step is a complex reaction with a change in the limiting stage of the reaction. Infrared spectra indicated that the decomposition proceeds via the gradual reduction of the ratio of the (NH₄)₂O to V₂O₅ units from the original 11 ratio in ammonium metavanadate, which may be written as (NH₄)₂O·V₂O₅, to V₂O₅.The assistance of Professor A. M. Heyns (University of Pretoria) and Professor K. L. Range (University of Regensburg) is gratefully acknowledged as well as the financial assistance of the University of Pretoria and the FRD.     

Synthesis,structure and the e.s.r. spectrum of the mixed-valence molybdovandate Na2(NH4)4[(VIVVV8Mo)O28] · 10H2O

The mixed-valence molybdovanadate compound Na₂(NH₄)₄[V^IVV^V ₈Mo)O₂₈] · 10H₂O [Vanadata(6-)tetradeca--oxotetra-₃-oxodi-₆-oxoheptaoxo(oxomolybdate) nonatetrammonium disodium, decahydrate] has been synthesized from sodium molybdate(VI) dihydrate and sodium metavanadate dihydrate in aqueous solution by adding NH₂OH · HCl. The molecular structure has been determined by X-ray diffraction and is based on the isopolydecavanadate structure. The molybdate atom is crystallographically disordered over 6MO₆ octahedral sites. The e.s.r. spectrum clearly indicates that one vanadium atom has the oxidation number +4.     

Copper(I) π-Complexes with Alkyne Ligands: Synthesis and Crystal Structure of M[CuCl2(HOCH2C≡CCH2OH)] (M = K+, NH+ 4)

Crystals of anionic complexes of the composition M[CuCl₂(HOCH₂CCCH₂OH)], where M = NH₄ ⁺ (I), K⁺ (II), were isolated from concentrated aqueous solutions of CuCl and MCl (M = NH₄ ⁺, K⁺) in the presence of 2-butyne-1,4-diol. Their structures were studied by X-ray diffraction analysis. Isostructural crystals I and II are orthorhombic; Z = 8, space group Ibam; a = 6.735(1) and 6.666(2) Å, b = 17.206(3) and 16.874(6) Å, c = 15.172(3) and 15.032(4) Å, V = 1758(1) and 1691(1) ų, respectively. The compounds are built of individual [CuCl₂(HOCH₂CCCH₂OH)] anions; the NH₄ ⁺ (I) or K⁺ (II) cations are arranged in the voids between the anions. The -coordinated Cu(I) atoms have trigonal-planar environment of two chlorine atoms and CC bond of the 2-butyne-1,4-diol molecule. The Cu–(CC) distances in the -core are 1.892(4) and 1.887(6) Å, CC are 1.233(5) and 1.228(5) Å in I and II, respectively. In complex I, additional hydrogen bonds Cl···H–NH₃ (Cl···H 2.43(4) Å) and O···H–NH₃ (O···H 1.97(3) Å) stabilize the structure.     

Umsetzung des Silberamidoselenates mit Ammoniak und Darstellung von Imidodiselenaten

Zusammenfassung Im Unterschied zu AgSO₃NH₂, das sich in flüssigem NH₃ glatt auflöst und quantitativ in den Aminkomplex [Ag(NH₃)₂] SO₃NH₂ übergeht, reagiert AgSeO₃NH₂ stark exotherm, wobei neben [Ag(NH₃)₂]SeO₃NH₂, NH₄SeO₃NH₂ und sehr kleinen Mengen einer bisher nicht identifizierten Substanz durch Kondensation, die etwa zu 60% verläuft, auch das Trisilbersalz der Imidodiselensäure als Aminkomplex [Ag(NH₃)₂]₃[O₃Se–N–SeO₃] entsteht.Nach einem einfachen Reinigungsverfahren wurde aus diesem Komplex Ag₃[O₃Se–N–SeO₃] erhalten und daraus die Imidodiselenate Na₃[O₃Se–N–SeO₃] · 3 H₂O, K₃[O₃Se–N–SeO₃] · H₂O, (NH₄)₃[O₃Se–N–SeO₃] und Ba₃[O₃Se–N–SeO₃]₂ · 5H₂O als kristalline Substanzen dargestellt, die näher charakterisiert und thermogravimetrisch und differentialthermoanalytisch untersucht wurden.

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Reaction of silver amidoselenate with ammonia and preparation of imidodiselenates

Contrary to AgSO₃NH₂, which dissolves in liquid NH₃ with quantitat. conversion to [Ag(NH₃)₂]SO₃NH₂, AgSeO₃NH₂ in a strongly exothermic reaction yields several products: [Ag(NH₃)₂]SeO₃NH₂, NH₄SeO₃NH₂, small amounts of an as yet unidentified compound, and in a condensation reaction to about 60% the amine complex of the trisilver salt of imido-diselenic acid.A simple purification gives Ag₃[O₃Se–N–SeO₃], and from this the crystalline imido-diselenates Na₃[O₃Se–N–SeO₃] · 3 H₂O, K₃[O₃Se–N–SeO₃] · H₂O, (NH₄)₃[O₃Se–N–SeO₃] and Ba₃[O₃Se–N–SeO₃]₂ · 5 H₂O where prepared and characterized thermogravimetrically, and by the method of differential thermoanalysis.

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Mit 3 Abbildungen

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K. Dostál undA. Rika, Z. Chem.8, 153 (1968). (Vorläufige kurze Mitteilung).     

Selected-control hydrothermal synthesis and formation mechanism of 1D ammonium vanadate

Selective-controlled structure and shape of ammonium vanadate nanocrystals were successfully synthesized by a simple hydrothermal method without the presence of catalysts or templates. It was found that tuning the pH of the growth solution was a crucial step for the control of the phase-compositional, structure and morphology transformation. The final products were NH₄V₄O₁₀ nanobelts, (NH₄)₂V₆O₁₆·1.5H₂O nanowires, and (NH₄)₆V₁₀O₂₈·6H₂O nanobundles, respectively, when the pH of the growth solution varied from 2.5 to 1.5, then to 0.5. The hydrogen bonding interaction and the surface free energies were responsible for the formation of the ammonium vanadates with the different structure and morphology. The conductivity measurements showed the one-dimensional (1D) ammonium vanadates were semiconductors at room temperature. The conductivity of 1D ammonium vanadates varied from 1.95×10⁻⁴ to 2.45×10⁻³ S cm⁻¹ due to the different structures.     

Decavanadates with [Et3NH] and [Me2HN(CH2)2NHMe2]: Variation in protonation state and self-assembly

Synthesis, thermal behaviour and crystal structures of [Et₃NH]₄[V₁₀O₂₆(OH)₂] (1) and [Me₂HN(CH₂)₂NHMe₂]₃[V₁₀O₂₈] · 4H₂O (2) are reported. In the crystal lattice of 1, the anions form discrete dimers via O–H···O hydrogen bonds and the cations are connected to the respective anions through N–H···O hydrogen bonds. On the other hand, 2 forms a complex three-dimensional network due to involvement of the cations, the anions and the lattice water in O–H···O and N–H···O hydrogen bonds.     

Potentiometrische säure-base-titrationen in alkalisulfatschmelzen

Using the Pt-(O₂) electrode as an indicator electrode for the O^2? concentration of a sulphate melt, potentiometric acid-base titrations have been carried out at 625°C in the eutectic Li₂SO₄-K₂SO₄-Na₂SO₄ melt. Na₂CO₃ has been used as an O^2? donor, and MoO₃, K₂Cr₂O₇, NaPO₃, Na₄P₂O₇ and V₂O₅ were used as acid species. While the equivalence point is at an acid/Na₂CO₃ molar ratio of 1:1 with MoO₃, K₂Cr₂O₇, NaPO₃ and Na₄P₂O₇, it is situated at about 0.3:1 in the system V₂O₅/Na₂CO₃.     

X-ray attenuation coefficient measurements for photon energies 4.508-13.375 keV in Cu, Cr and their compounds and the validity of the mixture rule

To investigate the validity of the mixture rule which is used to compute the mass attenuation coefficients in compounds, the total mass attenuation coefficients for Cu, Cr elements and Cu₂O, CuC₂O₄, CuCl₂·2H₂O, Cu(C₂H₃O₂)₂·H₂O, Cr₂O₃, Cr(NO₃)₃, Cr₂(SO₄)₃·H₂O, Cr₃(CH₃CO₇)(OH)₂ compounds were measured at photon energies between 4.508 and 13.375 keV by using the secondary excitation method. Ti, Mn, Fe, Ni, Zn, Ge, As, Rb elements were used as secondary exciters. 59.5 keV gamma rays emitted from an annular source were used to excite the secondary exciters and Kα (K-L₃, L₂) rays emitted from the secondary exciter were counted by a Si(Li) detector with a resolution of 160 eV at 5.9 keV. Our measurements indicate that the mixture rule is not a suitable method for the computation of mass attenuation coefficients of compounds especially at an energy that is near the absorption edge. Obtained values were compared with theoretical values.     

Chemical effects of heavy metals on the hydration of calcium sulphoaluminate 4CaO·3Al2O3·SO3

The system 4CaO·3Al₂O₃·SO₃-CaSO₄·2H₂O-Ca(OH)₂ was hydrated in the presence of ten dopants, specifically soluble salts of heavy metals.When added in 10% amount, the effect of each salt is strongly evident at shorter curing times, the hydration kinetics being more favoured in the order Pb(NO₃)₂2CrO₄< Cd(NO₃)₂< Zn(NO₃)₂t~Mn(NO₃)₃=K₂MoO₄3)₂3)₂3)₃3)₃. At longer curing times the differences among the systems decrease significantly.The 28-day compressive strength is almost the same for all the systems except those containing Pb(NO₃)₂, K₂MoO₄ and K₂CrO₄.     

The homogeneity range of lyonsite-type phase existing in the CrVO4 - Co3V2O8 system

In the work presented here, the way of obtaining the phase with general formula Co_3+1.5xCr_2–x(VO₄)₄ (0 ≤ × < 0.4) is demonstrated. A new phase is detected in CrVO₄ - Co₃V₂O₈ that is formed in one of the intersection of the ternary CoO - V₂O₅ - Cr₂O₃ system. Monophasic Co₃Cr₂(VO₄)₄ (Co_3+1.5xCr_2−x(VO₄)₄, where × = 0) was obtained from both a mixture comprising CrVO₄ and Co₃V₂O₈ as well as from the mixture of CoV₂O₆ with CoCr₂O₄. The Co_3+1.5xCr_2−x(VO₄)₄ is isotypic with the those demonstrating the lyonsite-type structure. The temperature of melting for the new compound was established using the DTA methods.      

Synthesis and Crystal Structure of Ammonium Dimolybdatouranylate Monohydrate (NH4)2[UO2(MoO4)2] · H2O

The crystal structure of the complex (NH₄)₂[UO₂(MoO₄)₂] · H₂O is determined. The unit cell parameters are a= 7.916, b= 10.885, c= 13.476 Å, = 98.40°, V= 1148.8 ų, space group P2₁/c, Z= 4, (calcd) = 3.452 g/cm³, R= 0.0406, R _w= 0.0850. The coordination polyhedron of the uranium atom is a pentagonal bipyramid with its equatorial plane formed by oxygen atoms of five MoO₄groups.