Structure and properties of Li<Subscript>2</Subscript>Zn<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> crystals activated with copper and chromium ions

Based on the corrected phase diagrams proper growth conditions for Li2Zn2(MoO₄)₃ crystals are selected. Large crystals (up to 100 mm), both impurity-free and activated by transition metal ions (Cu, Cr), are grown by the low-gradient Czochralski method. By the EPR method the charge state and structural position of copper and chromium ions are determined. The performed studies of luminescent properties show that for impurity-free crystals luminescence with λ = 388 nm with a two-exponential luminescence decay with τ₁ = 2 ns and τ₂ = 6 ns is observed at room temperature. At 77 K for both impurity-free crystals and those activated with transition metal ions luminescence with λ = 560 nm and the luminescence lifetime τ = 100 ns is observed, the intensity of luminescence with λ = 560 nm depending on the nature and concentration of transition metal ions. Cation vacancies responsible for the charge compensation of impurity transition metal ions are assumed to be also responsible for low-temperature luminescence.     

Structures and phase transitions in (K<Subscript>1-x</Subscript>Rb<Subscript>x</Subscript>)<Subscript>2</Subscript>SeO<Subscript>4</Subscript>

Summary The phase diagram of the mixed crystal (K_1-xRb_x)₂SeO₄ was determined by means of thermal analysis and neutron scattering experiments. The hexagonal to orthorhombic phase transition line exists for any x. The normal-incommensurate phase transition temperature decreases continuously with increasing Rb content. However, the incommensurate-commensurate phase transition was not observed except for K₂SeO₄. According to the clear softening of the Σ₂- Σ ₃ phonon branches and the finite frequency at 0 K for x>0.34, an existence of the hypothetical phase transition was confirmed.     

Synthesis and crystal structure of (NH<Subscript>4</Subscript>)(CN<Subscript>3</Subscript>H<Subscript>6</Subscript>)[UO<Subscript>2</Subscript>(SeO<Subscript>3</Subscript>)<Subscript>2</Subscript>]

Single crystals of (NH₄)(CN₃H₆)[UO₂(SeO₃)₂] (I) are synthesized and studied by X-ray diffraction analysis. The compound crystallizes in the triclinic crystal system with the unit cell parameters: a = 7.0051(2) Å, b = 9.4234(3) Å, c = 9.5408(3) Å, α = 88.727(1)°, β = 70.565(1)°, γ= 77.034(1)°, space group P ₁, Z = 2, R = 0.0224. The main structural units of crystals I are the [UO₂(SeO₃)₂]^2? chains of the crystal-chemical group AB²B₁₁ (A = UO ₂ ²⁺ , B₂= SeO₃ ^2?, B₁₁= SeO₃ ^2?) of the uranyl complexes. The uranium-containing complexes are joined into a three-dimensional framework by the ammonium and guanidinium ions and a system of hydrogen bonds.     

Ionic mobility in ammonium-rubidium heptafluorozirconate (NH<Subscript>4</Subscript>)<Subscript>2.4</Subscript>Rb<Subscript>0.6</Subscript>ZrF<Subscript>7</Subscript> by (<Superscript>1</Superscript>H, <Superscript>19</Superscript>F) NMR data

NMR (¹⁹F, ¹H) methods are used to study ionic mobility in heptafluorozirconate (NH₄)_2.4Rb_0.6ZrF₇ in a range of temperatures from 150 K to 430 K. Types of ionic movements are determined, and their activation energy is evaluated. As a result of a phase transition a modification forms in which diffusion in the ammonium sublattice and isotropic reorientations of ZrF ₇ ^3? complex anions are observed. According to preliminary data, due to diffusion of ammonium ions the compound has relatively high ionic conductivity (σ ≈ 8.3 × 10^?5 S/cm at 423 K).     

Dielectric constant and dielectric relaxation in aqueous solutions of K<Subscript>2</Subscript>[PdCl<Subscript>4</Subscript>] and K<Subscript>2</Subscript>[PtCl<Subscript>4</Subscript>]

The MW-dielectric properties of aqueous solutions of K₂[PtCl₄] (I) and K₂[PdCl₄] (II) were studied at 298 and 313 K in the frequency range (12–25 GHz) corresponding to the maximum dielectric constant dispersion for water and aqueous solutions of these salts. The low-frequency conductivities were measured. The static dielectric constant, the dielectric relaxation time, and the enthalpy of activation of the dielectric relaxation of the solutions were determined. Compared to pure water, in solutions of salts I and II, the orientational mobility of water molecules is increased and the network of H-bonds is violated more strongly than that of most other ions with hydrophilic hydration. It was demonstrated for the first time that dielectric spectroscopy can be used for analyzing complexation processes in systems containing aqua and hydroxo chloride complexes of metals.     

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.     

Lithium-conducting solid electrolytes of Li<Subscript>4</Subscript>GeO<Subscript>4</Subscript>-Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> system with additions of zirconium ions

The effect of partial substitution of Zr⁴⁺ ions for Ge4+ ions in highly conducting lithium-cationic solid electrolyte Li_3.75Ge_0.75P_0.25O₄ is studied. It is found that the introduction of zirconium ions considerably raises the conductivity of basic electrolyte in the high-temperature range. For the optimal composition, the conductivity is 2.82 × 10⁻¹ S cm⁻¹ at 400°C and 1.55 S cm⁻¹ at 700°C. Possible reasons for the effects are discussed.     

A Novel Uranyl Complex with Dimeric Lacunary Polyoxoanion: [(A-α-SiW<Subscript>9</Subscript>O<Subscript>33</Subscript>)<Subscript>2</Subscript>K{UO<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)}<Subscript>2</Subscript>]<Superscript>11−</Superscript>

A novel uranyl complex with dimeric lacunary polyoxoanion like open-mouthed clam, Na₅[(A-α-SiW₉O₃₃H₃)₂K{UO₂(H₂O)}₂], was prepared and characterized by elemental analysis, infrared and ultraviolet–visible spectroscopy and single crystal X-ray diffraction. In the anion, two A-α-SiW₉O₃₄¹⁰⁻ groups share two terminal oxygen atoms O_d′ derived from removal of three corner-shared W atoms from saturated α-Keggin anion, forming a dimeric anion with an open mouth in which potassium ion and uranyl ions are coordinated. Uranium atom adopts a pentagonal bipyramidal geometry. The coordinating anions are linked by sodium ions via coordination of terminal or bridging oxygen atoms, forming two-dimensional layer arrangement. Between the layers are the hydrogen bonds from which a supramolecular architecture is created. UV–VIS spectrum gives W–O and U–O charge transfer transitions at 230–265 and 432 nm, showing the change of geometry of the polyanion and weakening of the U–O bonds of the uranyl cation. Electronic supplementary material The online version of this article () contains supplementary material, which is available to authorized users.     

Low-temperature heat capacity of sodium erbium molybdophosphate Na<Subscript>2</Subscript>Er(MoO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)

Adiabatic calorimetry is used to measure the low-temperature heat capacity of Na₂Er(MoO₄)(PO₄)from 6.41 to 347.87 K. Experimental data are used to calculate the thermodynamic functions of Na₂Er(MoO₄)(PO₄), which at 298.15 K are as follows: C _p ⁰ (298.15 K) = 243,3 ± 0.4 J/(K mol), S ⁰(298.15 K) = 312.8 ± 0.8 J/(K mol), H ⁰(298.15 K) ? H ⁰(0 K) = 45280 ± 90 J/mol, and Φ⁰(298.15 K) = 136.1 ± 0.3 J/(K mol). A diffuse heat-capacity anomaly associated with splitting of the Stark levels (Schottky anomaly) is discovered in the low-temperature region.     

Ytterbium tris(hexafluoroacetylacetonate) Yb(C<Subscript>5</Subscript>O<Subscript>2</Subscript>HF<Subscript>6</Subscript>)<Subscript>3</Subscript>: The composition of overheated vapor and sublimation thermodynamics

A mass spectrometric study of the saturated vapor over ytterbium tris(hexafluoroacetylacetonate) Yb(hfa)₃ (hfa = CF₃-C(O)-CH-C(O)-CF₃) and of the vapor overheated up to the thermal decomposition temperature of the complex is presented. The vapor composition changes markedly with increasing temperature. At T ≈ 370 K, the mass spectrum of the vapor over Yb(hfa)₃ indicates the presence of ions containing one to three metal atoms. As the temperature is raised, the ion currents due to oligomer ions decrease. The oligomers are not detected at T > 440 K. The total decomposition temperature of Yb(hfa)₃ is 663(9) K. The second-law enthalpy of sublimation (ΔH _s^o (380 K)) is 134 ± 7 kJ/mol for the monomer and 138 ± 10 kJ/mol for the dimer. The enthalpy of dissociation of the dimer into monomer molecules is nearly equal to the enthalpy of sublimation of the monomer and dimer: ΔH _dis(380 K) = 130 ± 15 kJ/mol.     

Structure and electric properties of Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-NaPO<Subscript>3</Subscript> glasses

The influence of the SO₄²⁻ ion on the temperature and concentration dependences of electric conductivity and the structure of sodium phosphate oxide glasses was studied. The increased electric conductivity of sulfate-phosphate glasses was explained by the formation of mixed sulfate-phosphate fragments with terminal SO₄²⁻ ions in the structure of glasses in the Na₂SO₄-NaPO₃ system. The dissociation energies of the sodium sulfate fragments are lower than those of pure oxide sodium phosphate structural units. As a result, the number of dissociated sodium ions increases, the activation energy of electric conductivity falls, and the conductivity (at 25°C) increases approximately 270-fold relative to the conductivity of NaPO₃. The arrangement of SO₄²⁻ ions in the structure was evaluated from the IR spectra of the glasses.     

Magnetic properties of a dinuclear complex (2,3-Me<Subscript>2</Subscript>C<Subscript>5</Subscript>H<Subscript>3</Subscript>N)<Subscript>2</Subscript>Fe<Subscript>2</Subscript>(μ-OOCCMe<Subscript>3</Subscript>)<Subscript>4</Subscript> with “China lantern” structure

Magnetic characteristics of the dinuclear complex (2,3-Me₂C₅H₃N)₂Fe₂(μ-OOCCMe₃)₄ (1) were studied in the temperature interval 2–300 K. The magnetic behavior of complex 1 was interpreted in terms of the orbital-dependent exchange theory with allowance for the temperature dependence of the populations of the split ⁵T_2g ground-state components of the Fe^II ions. The calculated values of the orbital-dependent exchange parameters are in good agreement with the results reported for dinuclear carboxylates of other 3d-transition metals and suggest the existence of strong ferromagnetism in some types of heterodinuclear carboxylates.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2035–2039, October, 2004.     

Ionic conductivity of bismuth oxofluoride BiO<Subscript>0.1</Subscript>F<Subscript>2.8</Subscript> with tysonite-type structure (LaF<Subscript>3</Subscript>)

The complex impedance method in the temperature range of 291–660 K was used to study conductivity of oxofluoride BiO_0.1F_2.8 belonging to the tysonite structural type (LaF₃). Bismuth oxofluoride was synthesized using a solid-phase method at 770–870 K for 1–2 h in an argon atmosphere. Heterovalent substitution of fluoride ions F⁻ by oxygen ions O²⁻ in the anionic BiF₃ matrix sublattice results in high ionic conductivity (∼0.1 S/cm at 660 K) of BiO_0.1F_2.8 ceramic samples.     

Solid Solutions of the System V<Subscript>2</Subscript>O<Subscript>5</Subscript>-V<Subscript>2</Subscript>O<Subscript>4</Subscript>-TiO<Subscript>2</Subscript> in Air

Gravimetry in combination with X-ray phase analysis, X-ray crystallography, and X-ray densitometry were used to determine the contents of V⁵⁺, V⁴⁺, and Ti⁴⁺ ions and vacancies in solid solutions formed by the reaction of V₂O₅ with TiO₂ in air at atmospheric pressure.     

The thermochemical characteristics of the LnCl<Superscript>−</Superscript><Subscript>4</Subscript> and Ln<Subscript>2</Subscript>Cl<Superscript>−</Superscript><Subscript>7</Subscript> negative ions

The literature data on the thermochemical characteristics of negative LnCl^? ₄ and Ln₂Cl^? ₇ ions (from lanthanum to lutetium inclusive) in the gas phase are systematized. The enthalpies of ion-molecular and ion-ion reactions with the participation of these ions were calculated and used to determine the enthalpies of formation of the ions for the whole lanthanide series.     

Solubility of Eu<Subscript>2</Subscript>(SeO<Subscript>3</Subscript>)<Subscript>3</Subscript> and sorption of Eu(III) onto TiO<Subscript>2</Subscript> in the presence of Se(IV)

Metal ions sorption can be significantly affected by the presence of other sorbates, especially of complexing ligands. In this study, the effect of Se(IV) on Eu(III) sorption onto TiO₂ at different pH and Eu(III) concentration was investigated. Se(IV) was found to enhance Eu(III) sorption as a function of Se(IV) concentration. Constant capacitance model was successfully used to interpret the sorption experimental data. The solubility product of Eu₂(SeO₃)₃ at ambient temperature was investigated to highlight the sorption mechanism of ternary sorption system. The pK _sp value of Eu₂(SeO₃)₃ was found to be 31.51 ± 0.95.     

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.     

Specific heat on Sr<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and Sr<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>7</Subscript>

Summary Specific heats on the single crystals of Sr₂Nb₂O₇, Sr₂Ta₂O₇ and (Sr_1-xBa_x)₂Nb₂O₇ were measured in a wide temperature range of 2-600 K. Heat anomalies of a λ-type were observed at the incommensurate phase transition of T_INC (=495 K) on Sr₂Nb₂O₇ and at the super-lattice phase transition of T_SL (=443 K) on Sr₂Ta₂O₇; the transition enthalpies and the transition entropies were estimated. Furthermore, a small heat anomaly was observed at the low temperature ferroelectric phase transition of T_LOW (=95 K) on Sr₂Nb₂O₇. The transition temperature T_LOW decreases with increasing Ba content x and it vanishes for samples of x>2%.     

Wetting and conductivity of BiVO<Subscript>4</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript> ceramic composites

The conductivity and transport number of oxygen ions of BiVO₄-(5, 7, 10, 12) wt % V₂O₅ ceramic composites are measured using the four-probe and coulomb-volumetric methods, respectively, in the temperature range from 500 to 660°C. The phase transition of wetting of grain boundaries with eutectic melt at 640°C is discovered. It is shown that the grain boundary wetting significantly raises the ionic conductivity of composites.     

Thermodynamic properties of silicate glasses and melts: V. Systems CaB<Subscript>2</Subscript>O<Subscript>4</Subscript>-CaSiO<Subscript>3</Subscript> and Ca<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>-CaSiO<Subscript>3</Subscript>

Thermodynamic properties of melts of the CaB₂O₄-CaSiO₃ and Ca₂B₂O₅-CaSiO₃ systems were determined by the method of high-temperature mass-spectrometry. The melts of these systems are characterized by negative deviations from the ideal behavior at 1800 K.