Heat capacities and thermodynamic functions of new nanosized ferro-chromo-manganites LaM<Subscript>0.5</Subscript><Superscript>II</Superscript>FeCrMnO<Subscript>6.5</Subscript> (M<Superscript>II</Superscript>–Mg,Ca, Sr,Ba)

The heat capacities of nanosized ferro-chromo-manganites LaM_0.5 ^IIFeCrMnO_6.5 (M^II–Mg, Ca, Sr, Ba) are measured via dynamic calorimetry in the temperature range of 298.15–673 K using an IT-S-400 instrument. It is established that the C°_p~f(T) function of LaM_0.5 ^IIFeCrMnO_6.5 (M^II–Mg, Ca, Sr, Ba) has λ-type effects, due probably to phase transitions of the second order. Considering the temperatures of the phase transitions, equations of the heat capacity of ferro-chromo-manganites LaM_0.5 ^IIFeCrMnO_6.5 (M^II–Mg, Ca, Sr, Ba) as a function of temperature are derived on the basis of experimental data. Thermodynamic functions Н°(Т)–Н°(298.15), S°(Т), and Ф ^хх(Т) are calculated in the temperature range of 298.15–675 K.     

Supramolecular Adduct of γ-Cyclodextrin and [{Re<Subscript>6</Subscript>Q<Subscript>8</Subscript>}(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>]<Superscript>2+</Superscript> (Q=S,Se)

Slow evaporation of water solution of [{Re₆S₈}(H₂O)₆]²⁺ generated in situ from [{Re₆S₈}(OH)₆]^4– in presence of γ-cyclodextrin (CD) leads to crystallization of {[{Re₆S₈}(H₂O)₆] ? [γ-CD]}(NO₃)₂·12H₂O (1·12H₂O) supramolecular complex, which was characterized by single-crystal X-ray diffraction crystallography, IR-spectroscopy, thermogravimetric and elemental analyses. X-ray analysis confirms the formation of 1:1 {[{Re₆S₈}(H₂O)₆] ? [γ-CD]}²⁺ inclusion compound in the solid state. However, no adduct formation was detected between [{Re₆S₈}(H₂O)₆]²⁺ and γ-cyclodextrin in solution, according to ¹H NMR spectroscopy. In the case of in situ generated [{Re₆Se₈}(H₂O)₆]²⁺ the reaction solution with γ-cyclodextrin is unstable and during the crystallization only amorphous precipitate has been obtained.     

Synthesis and transport properties of perovskite-like phases (Sr,Ba)<Subscript>4</Subscript>E<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>11 ± δ</Subscript> (E = Mn,Cr, Cu)

Synthesis of (Sr, Ba)₄Э₂Nb₂O_{11 ± δ} where E = Mn, Cr, Cu and solid solution (Sr_1?y Cu_y)_{6 ? 2x} Nb_{2 + 2x} O_{11 + 3x} is performed. By measuring the overall conductance of some solid-solution compositions it is established that the conductance increases with the cubic-lattice parameter and concentration of oxygen vacancies. Values of the conductance in humid air at T < 700°C are shown to increase as compared with dry air. Mass spectrometry analysis confirms the possibility of water incorporation into the complex-oxide structure out of a gas phase. Complex certification of samples of the composition (Sr, Ba)₄E₂Nb₂O₁₁ where E = Mn, Cr, Cu is performed. It is established that the decrease in the overall electroconductance occurs in the series Sr₄Mn₂Nb₂O₁₁ > Ba₄Mn₂Nb₂O₁₁ > Sr₄CrMnNb₂O₁₁ > Sr₄Cu₂Nb₂O₁₁. Investigation of the overall electroconductance in dry and moist atmospheres shows that the effect of humidity exerts no influence on the values of the overall electroconductance. The oxygen-ion constituent of conductance is determined by the Arzhannikov method and is also evaluated from a σ,pO₂ dependence. It is established that the presence of an element with a variable oxidation degree for compositions of the type Sr₄E₂Nb₂O₁₁ leads to an increase in the contribution made by the electronic constituent. In so doing, the magnitude of the oxygen-ion conductance practically does not alter. Thermal and mass spectrometry analyses show that, for the Sr₄E₂Nb₂O₁₁ compositions where E = Mn, Cr, Cu, there occurs no water intercalation into structure, correspondingly, there is observed no appearance of a protonic constituent of conduction.     

Conduction and Transport Numbers in Metacomposites MeWO<Subscript>4</Subscript> ⋅ WO<Subscript>3</Subscript> (Me = Ca,Sr, Ba)

The conduction and transport numbers of charge carriers for composites in the systems MeWO₄-WO₃ (Me = Ca, Sr, Ba) are studied as a function of the temperature and the activity of oxygen in a gas phase. The transport numbers are determined by an emf method and are estimated from dependences of conductance on the activity of oxygen in a gas phase. The deficiencies of the given procedure as applied to investigation of properties of composite phases are analyzed. The materials under study are classified with a class of metacomposites. The concentration intervals of the ionic, mixed, and electronic conductions are determined. The conduction of composites of compositions (100 − x)MeWO₄ ⋅ xWO₃ is predominantly ionic at x ≤ 10 (Me = Ca), x ≤ 60 (Me = Sr), and x ≤ 45 (Me = Ba). The obtained data are explained in the framework of a model that represents a composite as a distributed matrix system where a film of surface phase MeW-s with a high mobility of oxygen ions plays the role of a connected matrix. It is presumed that the surface phase MeW-s possesses double-sided surface activity (α _MeW-s ≤ ) and a higher mobility with respect to MeWO₄ and WO₃. The discovered anomalies of dependences (T) and partial dependences , σ_el(T) are explained by a change in the stoichiometry, morphology, and the degree of connectedness of surface phase MeW-s caused by with a change in the temperature and composition of composites.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 680–693.Original Russian Text Copyright © 2005 by Neiman, Pestereva, Sharafutdinov, Kostikov.Published on the basis of a report delivered at the VII Meeting on Fundamental Problems in Solid-State Ionics (Chernogolovka-2004).     

Synthesis and structure of novel coordination compounds based on [Re<Subscript>6</Subscript>Q<Subscript>8</Subscript>(CN)<Subscript>6</Subscript>]<Superscript>4–</Superscript> (Q = S,Se) and (SnMe<Subscript>3</Subscript>)<Superscript>+</Superscript>

The reactions of SnMe₃Cl with salts of the cluster anionic complexes [Re₆Q₈(CN)₆]^4? (Q = S, Se) gave novel complexes [{(SnMe₃)₂(OH)}₂{SnMe₃}₂{Re₆S₈(CN)₆}] (I), (Me₄N)₂[{SnMe₃(H₂O)}₂{Re₆Se₈(CN)₆}] (II), [{(SnMe₂)₄(μ₃-O)}₂{Re₆Se₈(CN)₆}] (III), and [(SnMe₂)₄(μ₃-O)₂(μ₂-OH)₂(H₂O)₂][{SnMe_{3 2}{Re₆Se₈(CN)₆}] (IV). The structures of I–IV were determined by X-ray diffraction. Compounds I, IV have the chain structures with the CN-SnMe₃-NC bridges between the cluster anions [Re₆Q₈(CN)₆]^4?. Compound II contains isolated fragments {SnMe₃(H₂O)}₂{Re₆Se₈(CN)₆}^2?. In the polymer framework of compound III, the cluster anionic complexes [Re₆Se₈(CN)₆]^4? are bound by the complex cations [(SnMe₂)₄(μ₃-O)₂]⁴⁺ formed due to the hydrolysis of the initial (SnMe₃)Cl.     

Crystal structure of Mg pivalate hydrate Mg(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>(Piv)<Subscript>2</Subscript> · 3H<Subscript>2</Subscript>O

Single crystals of Mg pivalate hydrate, Mg(H₂O)₆(Piv)₂ · 3H₂O (HPiv = (CH₃)₃CCOOH) are synthesized and their structure is determined by X-ray diffraction method. The crystals are rhombic: a = 10.917(2) Å, b = 12.625(2) Å, c = 31.394(8) Å, Z = 8, space group Pbca, R ₁ = 0.0525. The Mg atom has octahedral surrounding of the O atoms of water molecules (Mg-O 2.044–2.137 Å). The cationic chains of [Mg(H₂O)₆] _∞ ²⁺ lie in the voids of doubled network anionic layers of [(H₂O)₃(Piv)₂] _∞∞ ^2? . Inside the layer, the pivalate anions alternate with water molecules in the xy plane, being bonded to them by hydrogen bonds. The cationic chains and the anionic layers are united into layered packs by hydrogen bonds between coordinated water molecules and pivalate anions and between coordinated and crystal hydrate water molecules.     

Thermodynamic characteristics of europium pivalate binuclear complexes Eu<Subscript>2</Subscript>(Piv)<Subscript>6</Subscript> and [Eu<Subscript>2</Subscript>(Piv)<Subscript>6</Subscript> · (Phen)<Subscript>2</Subscript>]

Sublimation of europium pivalate binuclear complexes Eu₂(Piv)₆ and [Eu₂(Piv)₆ · (Phen)₂] (Piv = (CH₃)₃CCOO, Phen = C₁₂H₈N₂) in the temperature range of 383–660 K is studied by the Knudsen effusion method with mass-spectrometric analysis of the gas phase. The vaporization of Eu₂(Piv)₆ is shown to be accompanied by polymerization and the formation of Eu₂(Piv)₆ and Eu₄(Piv)₁₂ molecules. The saturated vapor over the mixed-ligand complex of europium pivalate with o-phenanthroline consists of Phen, Eu₂(Piv)₆, and Eu₄(Piv)₁₂ molecules. The partial pressures of the gas components, as well as the standard enthalpies of sublimation and dissociation of the reaction proceeding with removal of phenanthroline have been determined.     

Structure and stability of endohedral complexes <Superscript>4/2</Superscript>X@(HAlNH)<Subscript>2</Subscript> (X = N,P, As,C<Superscript>−</Superscript>, Si<Superscript>−</Superscript>)

The structures of a closo-hedral cluster (HAlNH)₁₂ and endohedral complexes ^4/2X@(HAlNH)₁₂ (X = N, P, As, C⁻, Si⁻) are studied by density functional theory (DFT) at the B3LYP/6-31G(d) level. The geometries, natural bond orbital (NBO), vibrational frequency (ν₁), energetic parameters, magnetic shielding constants (σ), and nucleus independent chemical shifts (NICSs) are discussed. It is found that all guest species are minima at the cage center. Inclusion energies (ΔE _inc) of all species are negative except those of ⁴N and ^4/2P. In all species, the endohedral quartet states (⁴X) are energetically less favorable than their doublet states (²X). The calculations predict that caged X states only donate <0.50 e to the cage and preserve their unencapsulated ground states.     

Structural investigation of salts containing ions [Pd(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>]<Superscript>2+</Superscript> and [IrF<Subscript>6</Subscript>]<Superscript>2–</Superscript>

Double complex salts (DCS) α-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/m, a = 6.3181(3) Å, b = 10.8718(5) Å, с = 7.4526(4) Å, β = 103.568(2)°), β-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/с, a = 8.5773(3) Å, b = 10.8791(4) Å, с = = 12.6741(3) Å, β = 122.497(2)°), [Pd(NH₃)₄]₃[IrF₆]₂Cl₂·H₂O (P-1, a = 7.6080(2) Å, b = 7.6274(2) Å, с = 11.8070(3) Å, β = 122.497(2)°), and [Pd(NH₃)₄]₂[IrF₆]NO₃ (Fm-3m, a = 11.21210(10) Å) have been synthesized and structurally characterized for the first time. The existence of polymorphs for the DCS has been revealed. The influence of the chemical composition of the initial reagents on the reaction course and, respectively, the products, has been demonstrated. A hypothesis on the influence of the second coordination sphere on the formation of one or the other polymorph of the DCS has been suggested. It has been shown that the series α-[Pd(NH₃)₄][МF₆]·H₂O (M = Pt, Pd) exhibits isostructurality.     

Magnetism study of C<Superscript>I</Superscript><Subscript>x</Subscript>Co<Subscript>y</Subscript>[Fe(CN)<Subscript>6</Subscript>]·zH<Subscript>2</Subscript>O (C<Superscript>I</Superscript>=Rb,Cs) Prussian blue nanoparticles

We synthesized a series of cobalt-iron Prussian blue analogues in the form of nanocubes with which we tuned the amount of Cesium cation in the tetrahedral sites of the structure and varied nature of the alkali cation in the compound adopting a single microemulsion technique. Structure and morphology of the compound had been investigated by combining energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma (ICP), thermo-gravimetry analysis (TGA), infrared spectroscopy (IR), powder X-ray diffraction (XRD) and Transmission electron microscopy experiments (TEM). To directly determine the coercivity, remanence and Curie temperature, superconducting quantum interference device magnetometer (SQUID) was performed. Our investigation suggests that the amount and nature of the alkali cation are critical parameters for understanding the magnetic properties of the nanoparticles.     

Crystal structure of Pb<Subscript>2</Subscript>[Fe(CN)<Subscript>6</Subscript>]NO<Superscript>3</Superscript>·5.5H<Subscript>2</Subscript>O

Synthesis of a mixed complex compound Pb₂[Fe(CN)₆]NO₃·5.5H₂O is described. The results of its X-ray structural investigation are presented. Crystal data: C₆H₁₁FeN₇O_8.50Pb₂: a = 7.2582(6) Å, b = 21.838(3) Å, c = 11.612(1) Å; β = 107.91(1)°, V = 1751.4(3) ų, Z = 4, d_calc = 2.986 g/cm³, space group P2₁/m, R = 0.038. The compound has a framework polymer structure.     

Chemical Bonding in the Complexes XeF<Stack><Subscript>5</Subscript><Superscript>+</Superscript></Stack>XF<Stack><Subscript>6</Subscript><Superscript>−</Superscript></Stack> (X = P,As, Sb,and Bi)

Ab initio quantum-chemical calculations of the complexes XeF ₅ ⁺ XF ₆ ^? (X = P, As, Sb, and Bi) were performed with the use of relativistic pseudopotentials for heavy atoms and full-electron basis sets. The chemical bonds were characterized by the parameters of critical points (electron density, its Laplacian, total electron energy, and its kinetic and potential components). It was demonstrated that the interaction between the XeF ₅ ⁺ cation and the XF ₆ ^? anion in XeF ₅ ⁺ XF ₆ ^? follows a key-lock scheme involving directed interactions of bridging fluorine atoms F_b → Xe and that the structuring function of the lone electron pair of the Xe atom is to compensate the destabilizing electrostatic interaction between the Xe and X atoms bearing excess positive charges.     

Photochemistry of PtBr<Subscript>6</Subscript><Superscript>2−</Superscript> in aqueous solution

Photochemistry of the PtBr₆ ²⁻ complex in aqueous solution was studied by steady-state and laser flash photolysis (308 nm). The multistep photoaquation of the complex occurs in the nano-and microsecond time intervals without the formation of intermediate platinum(III) complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2277–2283, December, 2007.     

Transport properties of metacomposites in eutectic MAO<Subscript>4</Subscript>–V<Subscript>2</Subscript>O<Subscript>5</Subscript> systems (M = Ca,Sr; A = W,Mo)

Metal molybdates MMoO₄ (M = Ca, Sr) and their composites with vanadium oxide V₂O₅ were synthesized. An X-ray diffraction analysis confirmed that the obtained molybdates were single-phase, and the heterogeneous systems were two-phase. The temperature dependences of the total conductivity of the composites were studied. The ion transport numbers in the {CaMoO₄ · xV₂O₅} composites (x = 1–30 mol %) were studied by the EMF method. The conductivity of the composites at x ≤ 5 mol % was shown to be ionic. The conductivity of the composites was described using the mixing equation.     

Synthesis of dicationic μ-diborolyl triple-decker complexes [CpCo(μ-1,3-C<Subscript>3</Subscript>B<Subscript>2</Subscript>Me<Subscript>5</Subscript>)M(C<Subscript>6</Subscript>H<Subscript>6</Subscript>)]<Superscript>2+</Superscript> (M = Rh,Ir)

Dicationic triple-decker complexes [CpCo(μ-1,3-C₃B₂Me₅)M(C₆H₆)]²⁺ (M = Rh (3), Ir (4)) were synthesized by the reaction of [CpCo(μ-C₃B₂Me₅)MBr₂]₂ (M = Rh, Ir) with benzene in the presence of AgBF₄. The structure of 3(BF₄)₂ was determined by X-ray diffraction analysis.     

Experimental Determination of the Isotherm at 15°C of the System Mg<Superscript>2+</Superscript>/Cl<Superscript>−</Superscript>, SO<Subscript>4</Subscript><Superscript>2</Superscript>–H<Subscript>2</Subscript>O

Summary.  The diagram of the ternary system Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O was established at 15°C by means of analytical and conductimetric measurements. Three compounds were found in this diagram, which are MgSO₄·6H₂O, MgSO₄·7H₂O, and MgCl₂·6H₂O. The solubility field of MgSO₄·7H₂O is important whereas those of MgSO₄·6H₂O and MgCl₂·6H₂O are small. The compositions (mass-%) of the two invariant points determined by the two methods are: MgSO₄:MgCl₂=2.73:33.80 and MgSO₄: MgCl₂=3.38:28.91. Both the measured and the calculated isotherm at 15°C have been used for modelling of the diagram Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O between 0 and 35°C. The polythermal invariant point was approximately located between 15 and 10°C.  Corresponding author. E-mail: ariguib@planet.tn Received October 16, 2002; accepted (revised) December 3, 2002 Published online April 24, 2003 RID="a" ID="a" Dedicated to Prof. Dr. Heinz Gamsj?ger on the occasion of his 70^th birthday     

Nickel(II) and Iron(II) coordination compounds with octahydrotriborate(1–) anion [ML<Subscript>3</Subscript>]{B<Subscript>3</Subscript>H<Subscript>8</Subscript>}<Subscript>2</Subscript> (M = Fe<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript>; L = bipy,phen)

Methods of synthesis have been developed for new types of promising precursors of metal borides, coordination compounds [ML₃]B{₃H₈{₂ (M = Fe²⁺, Ni²⁺; L = bipy, phen), using modified procedures of synthesis of octahydrotriborate anion. Compounds [Ni(bipy)₃]B{₃H₈}₂, [Ni (phen)₃]B{₃H₈}₂ and [Fe(phen)₃]B{₃H₈}₂ were prepared and characterized by single-crystal X-ray diffraction.     

Thermodynamic Properties and Thermal Expansion of Tm<Subscript>2</Subscript>O<Subscript>3</Subscript> · 2ZrO<Subscript>2</Subscript> Solid Solution

The isobaric heat capacity of Tm₂O₃ · 2ZrO₂ solid solution was measured by adiabatic calorimetry and differential scanning calorimetry (DSC), and smoothed values of the enthalpy changes, entropy, and reduced Gibbs free energy in the temperature range 8–1200 K were calculated. Thermal expansion was studied by X-ray diffraction in the temperature range 298–1173 K.