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.     

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.     

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.     

Calorimetric determination of the thermodynamic properties of the alkali metal salts NaNO3, KNO3, Na2Cr2O7, K2Cr2O7 and their binary eutectic solutions

This work is part of more general project in thermal energy storage by means of the solid—liquid phase transformation. The phase diagrams were checked and slightly modified. A drop calorimeter was used to measure the enthalpies over a small temperature range near the melting points, so enabling the determination of the heats of fusion and the specific heats of the solid and liquid phases over these ranges.For NaNO₃, KNO₃, Na₂Cr₂O₇, K₂Cr₂O₇, NaNO₃KNO₃, NaNO₃Na₂Cr₂O₇, NaNO₃, K₂Cr₂O₇, KNO₃K₂Cr₂O₇ and Na₂Cr₂O₇K₂Cr₂O₇, the enthalpies in the solid and liquid states and the heats of fusion were found to be, respectively, in cal mole^?1; 9300, 12800, 3500 at 581 K; 10300, 12500, 2200 at 611 K; 23600, 29600, 6000 at 625 K; 25000, 34400, 9400 at 666 K; 5700, 8200, 2500 at 495 K; 10300, 13800, 3500 at 535 K; 8700, 11300, 2600 at 495 K; 11100, 13500, 2400 at 537 K; 20300, 23600, 3300 at 573 K. The results for the heats of fusion of the solutions are compared with values obtained by means of simple methods of estimation.     

Solubility in the system Na2Cr2O7 + 2NH4Cl ⇆ (NH4)2Cr2O7 + 2NaCl-H2O

The solubility in the water-salt quaternary reciprocal system Na₂Cr₂O₇ + 2NH₄Cl ⇆ (NH₄)₂Cr₂O₇ + 2NaCl-H₂O has been investigated for the first time at 25, 50, and 75°C. Using a formal analytical model, the boundaries of the phase fields have been determined, and the univariant lines and invariant points have been calculated. The experimental data have been used to calculate the temperature and concentration parameters of the circular isohydric process of potassium dichromate preparation with the participation of ammonium salts as intermediates.     

Effect of K2Cr2O7 Addition on Anodic Dissolution of NiS in Acid Sulfate and Ammonia Electrolytes

The depassivating effect of K₂Cr₂O₇ additions on the electrochemical dissolution of nickel sulfidein 0.5 M solutions of CuSO₄, Na₂SO₄, in 5.8 M NH₄OH was studied at 90°C.     

Relationships in formation of the active surface of vanadium-containing oxide systems for hydrocarbon dehydrogenation reactions in the presence of hydrogen acceptors

A study has been made of the catalytic properties of vanadium-aluminum and vanadium-magnesium oxide systems in the reaction of ethylbenzene dehydrogenation in the presence of nitrobenzene. The catalysts were prepared from NH₄VO₃ and the complex salts K₆V₁₀O₂₈·10H₂O, 2(NH₄)₂O·V₂O₅·2CrO₃·7H₂O, and (NH₄)₄V₆O₁₇·(NH₄)₂MoO₄. It was established that catalysts prepared from complex vanadium salts and --Al₂O₃ will operate for extended periods without loss of activity. The effects of CdO, K₂SO₄, KOH, ZnO, MoO₃, and Cr₂O₃ on the catalytic activity were investigated; the addition of Cr₂O₃ has the greatest effect. The process of coke formation on these catalysts has been investigated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1751–1757, August, 1991.     

The crystal structure of a complex cerium(III) molybdate containing a dimolybdate chain,Ce2(MoO4)2(Mo2O7)

Ce₂(MoO₄)₂(Mo₂O₇) crystallizes in the triclinic system with unit cell dimensions (from single-crystal data) a = 11.903(8), b = 7.509(5), c = 7.385(5) Å, α = 94.33(8), β = 97.41(8), γ = 88.56(7)°, and space group $\text{P}\text{1}\text{, z = 2}$. The structure was solved using Patterson (“P1 method”) and Fourier techniques. Of the 8065 unique reflections measured by counter techniques, 6314 with I ≥ 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.035 (R_w = 0.034). The structure of Ce₂(MoO₄)₂(Mo₂O₇) consists of dimolybdate chains of the K₂Mo₂O₇ and (NH₄)₂Mo₂O₇ type separated by isolated MoO₄ tetrahedra and cerium(III) polyhedra.     

Hydrogen peroxide oxidation of hydrocarbons catalyzed by Cr(VI) oxo compounds

>CrO₃, (NBu₄)₂CrO₄, (NBu₄)₂Cr₂O₇, and (NBu₄)Cr₄O₁₃ catalyze the hydrogen peroxide oxidation of cyclohexane, ethylbenzene, and styrene in acetonitrile. The active species is apparently a Cr(VI) peroxo complex.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 210–211, January, 1990.     

In situ Untersuchungen der Reaktion von Ammoniummonomolybdat, (NH4)2MoO4, mit Ammoniak: Die Struktur von (NH4)2[Mo3O10]

In situ Investigation of the Reaction of Ammonium Monomolybdate (NH₄)₂MoO₄ with Ammonia: The Structure of (NH₄)₂[Mo₃O₁₀] The reactivity of both polymorphs of (NH₄)₂MoO₄ with ammonia was investigated in a temperature range between 20 and 180 °C. Time and temperature controlled X‐ray powder diffraction as well as thermogravimetrical and differential thermal analysis were used to investigate this reaction.The formation of (NH₄)₂[Mo₃O₁₀] from (NH₄)₂MoO₄ is reversible in a humid and irreversible in a dry NH₃ gas flow. Heating (NH₄)₂MoO₄(mP60) under an atmosphere of humid NH₃ at about 170 °C forms (NH₄)₂[Mo₃O₁₀] and succesively cooling yields the (NH₄)₂MoO₄(mS60) polymorph. (NH₄)₂[Mo₃O₁₀] crystallises isostructural to the potassium compound with space group C2/c (No. 15) and lattice constants a = 1398.2(4), b = 804.1(2), b = 921.0(3) pm and β = 98.833(4)°.     

Synthesis of fullerene Γ-lactones by free radical reaction of C60 with ketones promoted by compounds of transition metals Cr(VI), Ce(IV)

One-step synthesis was developed for fullerene Γ-lactones by the reaction of C₆₀ with aromatic and aliphatic ketones in the presence of transition metal compounds CrO₃, K₂Cr₂O₇, (NH₄)₂Ce(NO₃)₆ ·6H₂O.     

Beiträge zum thermischen Verhalten wasserfreier Phosphate. IX. Darstellung und Kristallstruktur von Cr6(P2O7)4. Ein gemischtvalentes Pyrophosphat mit zwei- und dreiwertigem Chrom

Contributions on the Thermal Behaviour of Anhydrous Phosphates. IX. Synthesis and Crystal Structure of Cr₆(P₂O₇)₄. A Pyrophosphate Containing Di- and Trivalent Chromium Cr₆(P₂O₇)₄ (Cr₂²⁺Cr₄³⁺(P₂O₇)₄) can be obtained reducing CrPO₄ by phosphorus (950°C, 48 h, 100 mg iodine as mineralizer). By means of chemical transport reactions (transport agent iodine; 1050 → 950°C) the compound has been separated from its neighbour phases (Cr₂P₂O₇, CrP₃O₉) and crystallized (greenish, transparent crystals; edge length up to 0.3 mm). The crystal structure of Cr₆(P₂O₇)₄ (Spcgrp.: P-1; z = 1; a = 4.7128(8) Å, b = 12.667(3) Å, c = 7.843(2) Å, α = 89.65(2)°, β = 92.02(2)°, γ = 90.37(2) has been solved and refined from single crystal data (2713 unique reflections, 194 parameter, R = 0.035). Cr²⁺ is surrounded by six oxygen atoms which occupy the corners of an elongated octahedron (4 × d^{Cr? O} ≈? 2.04 Å; 2 × d^{Cr? O} ≈? 2.62 Å). The Cr³⁺ ions are also coordinated octahedraly (1.930 Å ≤ d_{Cr? O} ≤ 2.061 Å). The crystallographically independent pyrophosphate groups show nearly eclipsed conformation. The bridging angles (P? O? P) are 136.5° and 138.9° respectively.     

Preparation of lithium molybdenum oxide bronzes by a temperature gradient flux growth technique

Single crystals of the violet-red Li_0.9Mo₆O₁₇, violet-blue Li_0.32MoO₃, and the new blue Li_0.04MoO₃ bronzes have been grown by a temperature gradient flux growth method in evacuated quartz ampoules. Optimal growth conditions determined for each of the phases are reported. Li_0.9Mo₆O₁₇ is monoclinic, and a quasi-two-dimensional metallic conductor at room temperature, similar to K_0.9Mo₆O₁₇ · Li_0.04MoO₃ appears to be a new intercalation compound of MoO₃.     

Cryoscopic studies on some Tungstates and Vanadates in Molten KNO3

The depression of the freezing point of molten KNO₃, as solvent, was measured after the addition of small concentrations of the solutes: 1. WO₃, K₂WO₄, K₂W₂O₇ and 2. V₂O₅, Cs₂V₆O₁₆ and Rb₂V₆O₁₆. DTA-apparatus was used in the measurements. The results showed that the investigated tungstates and vanadates were dissociated in the melt with the formation of monotungstate (WO₄)^2? and orthovanadate (VO₄)^3?-ions.     

Effects of alkali metal ions on the thermal decomposition of ammonium heptamolybdate tetrahydrate

The thermal decomposition of pure ammonium heptamolybdate tetrahydrate (AHMT), and doped with Li⁺, Na⁺ and K⁺ ions was investigated using thermogravimetry, differential thermal analysis, infrared and X-ray diffraction techniques. Results obtained revealed that the decomposition of AHMT proceeded in three decomposition stages in which both NH₃ and H₂O were released in all stages. The presence of 0.5 mol % alkali metal ions enhances the formation of the intermediateb (NH₄)₂MO₇O₂₂·2H₂O while the decomposition of this intermediate into MoO₃ is slightly affected in the presence of all dopant concentrations used. The infrared absorption spectra of the thermal products of AHMT treated with 10 mol% alkali metal ions (AMI) at 350°C indicated a reduction of some Mo⁶⁺ ions. By heating of AHMT above 500°C in presence of 5 or 10 mol % of AMI, a solid-solid interaction between alkali metal oxides and MoO₃ giving rise to well crystallized alkali metal molybdates. finally the activation energies accompanied various decomposition stages were calculated.     

Molybdenum Bisphosphonates with Cr(III) or Mn(III) Ions

The synthesis of Mo^VI bisphosphonates (BPs) complexes in the presence of a heterometallic element has been studied. Two different BPs have been used, the alendronate ligand, [O₃PC(C₃H₆NH₃)(O)PO₃]^4? (Ale) and a new BP derivative with a pyridine ring linked to the amino group, [O₃PC(C₃H₆NH₂CH₂C₅H₄N)(O)PO₃]^4? (AlePy). Three compounds have been isolated, a tetranuclear Mo^VI complex with Cr^III ions, (NH₄)₅[(Mo₂O₆)₂(O₃PC(C₃H₆NH₃)(O)PO₃)₂Cr]·11H₂O (Mo₄(Ale)₂Cr), its Mn^III analogue, (NH₄)_4.5Na_0.5[(Mo₂O₆)₂(O₃PC(C₃H₆NH₃)(O)PO₃)₂Mn]·9H₂O (Mo₄(Ale)₂Mn), and a cocrystal of two polyoxomolybdates, (NH₄)₁₀Na₃[(Mo₂O₆)₂(O₃PC(C₃H₆NH₂CH₂C₅H₄N)(O)PO₃)₂Cr]₂[CrMo₆(OH)₆O₁₈]·37H₂O ([Mo₄(AlePy)₂Cr]₂[CrMo₆]). In this latter compound an Anderson-type POM [CrMo₆(OH)₆O₁₈]^3? is sandwiched between two tetranuclear Mo^VI complexes with AlePy ligands. The protonated triply bridging oxygen atoms bound to the central Cr^III ion of the Anderson anion develop strong hydrogen bonding interactions with the oxygen atoms of the bisphosphonate complexes. The UV–Vis spectra confirm the coexistence in solution of both POMs. Cyclic voltammetry experiments have been performed, showing the reduction of the Mo centers. In strong contrast with the reported Mo^VI BP systems, the presence of trivalent cations in close proximity to the Mo^VI centers dramatically impact the potential solid-state photochromic properties of these compounds.     

Preparation of sodium dimolybdate by the pyrolysis of sodium oxomolybdenum (VI) oxalate

Thermal studies on various oxalato complexes have been of immense interest as they yield finely divided, highly reactive oxides which are usually obtained at a much lower temperature than that required in the conventional method of preparation, i.e., heating a mixture of two or more constituents [1]. A survey of the literature reveals that the compounds having the general formula A₂[Mo₂O₅(C₂O₄)₂(H₂O)₂], where A = K⁺, NH⁺₄[2] and A = Cs⁺ [3], have been prepared and their thermal decomposition is studied, but no such information is available regarding the preparation and characterisation of Na₂[Mo₂O₅(C₂O₄)₂(H₂O)₂] (SMO), which forms the subject of study of this paper. Sodium dimolybdate (Na₂Mo₂O₇), the decomposition product of SMO, is obtained at 280°C, a temperature much lower than that required in the conventional method of preparation of heating a mixture of Na₂MoO₄ and MoO₃ [4].     

Die Selektivität Kristalliner Cer(IV)-Phosphatsulfathydrate gegenüber Li+, Na+, K+, Rb+, Cs+ und NH in absolutem Methanol und absolutem Dimethylsulfoxid

Selectivity of Crystalline Ce^IV Phosphate Sulphate Hydrates for Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and NH in Absolute Methanol and Absolute Dimethylsulphoxide The sequence of exchange capacities of Cerium(IV) phosphate sulphate hydrate (CePO₄)₂(HPO₄)_0.74(SO₄)_0.26 · 4,74 H₂O for alkalimetal ions and ammoniumions in absolute methanol at 25°C for the case of a small excess of the exchanger (in relation to the equivalent amount) is given by K⁺ > Rb⁺ ≥ NH₄⁺ > Cs⁺ > Na⁺ > Li⁺. Between the exchange capacity A of these cations and their ionic radii r (given by Ladd) exists the simple relation A = const./r. For Na⁺ the radius of the inner hydration shell must be considered. In absolute dimethyl-sulphoxide under the same conditions the sequence is K⁺ ≥ NH₄ > Rb⁺ > Na⁺ > Cs⁺ > Li⁺. For K⁺, NH₄, Rb⁺ and Cs⁺ the exchange capacity is given by A = const./r + const. · r⁴. The sequences of the alkali ions in both solvents are among the group of 13 sequences which are physicaly significant according to EISENMANNS 's theory. The results are compared with the observations made with water as solvent.     

Schwingungsspektren und Kraftkonstanten von Chrom(VI)-Sauerstoff-Verbindungen

The infrared and RAMAN spectra of Cr₃O, CrO₄O and CrO₃ have been measured and assigned. The force constant of a modified valence force field have been calculated and compared with the force constants of CrO, Cr₂O, CrO₃F^?, CrO₃Cl^?, CrO₂F₂ and CrO₂Cl₂. The valence force constant f_CrO depends almost linearly on the distance d(CrO). The bending frequency δ(CrOCr) has to be reassigned. The unit cell parameters of α- and β-Cs₂Cr₃O₁₀ and Cs₂Cr₄O₁₃ have been determined by means of Guinier X-ray powder techniques.     

Interaction in the Li2Mo3O10-CO(NH2)2-H2O system at 25°C

The solubilities and solid phases in the Li₂Mo₃O₁₀-CO(NH₂)₂-H₂O system at 25°C are studied. A compound of composition Li₂Mo₃O₁₀ · 6CO(NH₂)₂ · 4H₂O and lithium trimolybdate decahydrate Li₂Mo₃O₁₀ · 10H₂O are found to exist. The Li₂Mo₃O₁₀ · 6CO(NH₂)₂ · 4H₂O ray crosses the solubility isotherm, which indicates the congruent solubility of the double compound in water. The density, refractive index, dynamic viscosity, surface tension, electrical conductivity, and pH of saturated solutions of the system are determined. The molar volume, equivalent electrical conductivity, reduced conductivity, and solution ionic strength isotherms are calculated. A strong correlation between all the property isotherms and the solubility is observed.