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.     

Solid solutions (Ru,Nb)Sr<Subscript>2</Subscript>(Sm<Subscript>1.4</Subscript>Ce<Subscript>0.6</Subscript>)Cu<Subscript>2</Subscript>O<Subscript>10−δ</Subscript>: Synthesis,structure, and properties

Solid solutions of as-batch composition (Ru_1?x Nb _x )Sr₂(Sm_1.4Ce_0.6)Cu₂O_10?δ (the Ru,Nb)-1222 phase), where x = 0.0, 0.25, 0.50, 0.75, or 1.00, have been synthesized and characterized by X-ray diffraction. A correlation is proposed between the refined composition of the Ru-1222 and Nb-1222 phases and their structural features. With increasing oxygen concentration in the Ru-1222 phase, the superconducting transition temperature increases from T _c = 28 to T _c = 34 K. The composition and magnetic properties of the Ru-1222 phase are affected by the batch composition: unlike in Ru + RuO₂ mixtures, the presence of ruthenium in the batch decreases the oxygen proportion and increases the magnetic ordering temperature T _m; the phase of as-batch composition NbSr₂(Sm_1.4Ce_0.6)Cu₂O_10?δ is paramagnetic.     

Stable triangle (LiF)<Subscript>2</Subscript>–(KI)<Subscript>2</Subscript>–Li<Subscript>2</Subscript>CrO<Subscript>4</Subscript> of the quaternary reciprocal system Li,K∥F,I,CrO<Subscript>4</Subscript>

The quaternary reciprocal system Li,K||F,I,CrO₄ was partitioned into stable simplexes using graph theory. The system consists of five stable tetrahedra separated by four stable triangles. The chemical interaction between components was described based on the material balance written with account for occurring chemical reactions. Phase equilibria in the quasi-ternary system (LiF)₂–(KI)₂–Li₂CrO₄ were studied for the first time; in this system, the temperature and composition of a ternary eutectic were determined. The limited solubility of two liquid phases manifests itself in the concentration region adjacent to the LiF–KI quasibinary system. A three-dimensional model of the phase complex of the system was constructed in temperature– concentration coordinates.     

Phase equilibria,charge transport,and mass transport in Sr<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>-“M<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>” (M = Cd,Cu, Ni,and Zn) systems

Homogeneous fields of Sr_{4 − x} M _x Nb₂O₉ (M = Cd, Cu, Ni, or Zn) solid solutions were determined using powder X-ray diffraction. Phase fields were plotted proceeding from the tolerance factor t and electronegativity ratio $ \bar k_A /\bar k_B $ \bar k_A /\bar k_B with a satisfactory fit of experimental results. Thermogravimetry was used to establish the major kinetic laws of solid-phase synthesis (conversion, rate-controlling stage, and effective activation energy) in (4 − x)SrCO₃ + xMO + Nb₂O₅ powdery mixtures. Direct radiometry was used to determine ⁹⁰Sr, ⁶³Ni, and ⁶⁵Zn self-diffusion coefficients in solid solutions based on the Sr₄Nb₂O₉ phase. Electrical conductivity was measured as a function of temperature for all Sr₄Nb₂O₉-“M₄Nb₂O₉” samples. The conductivity of Sr_{4 − x} M _x Nb₂O₉ (M = Cd, Cu, Ni, or Zn) solid solutions has a mixed ion-electron character.     

Synthesis and physicochemical study of M<Subscript>4</Subscript>Na<Subscript>2</Subscript>V<Subscript>10</Subscript>O<Subscript>28</Subscript> · 10H<Subscript>2</Subscript>O (M=K,Rb, NH<Subscript>4</Subscript>)

The formation conditions and physicochemical properties of binary decavanadates M₄Na₂V₁₀O₂₈ · 10H₂O (M=K, Rb, NH₄), synthesized by crystallization from saturated solutions of the NaVO₃-MH₂AsO₄-H₂O systems, were studied by chemical analysis, X-ray powder diffraction, microscopy, thermogravimetry, and IR spectroscopy. To optimize the synthesis conditions of M₄Na₂V₁₀O₂₈ · 10H₂O, the ( 1-x)NaVO₃ · 2H₂O · xMH2AsO4-H₂O (0.2 ≤ x ≤ 0.8) isomolar series method was applied to studying the interaction in the NaVO₃-MH₂AsO₄-H₂O systems (M = K, Rb, Cs) at the 0.4 mol/L total molar concentration of NaVO₃ and MH₂AsO₄ in solutions. The studied M₄Na₂V₁₀O₂₈ · 10H₂O compounds were shown to be isostructural with triclinic crystals (Z= 1, space group P $ \bar 1 $ \bar 1 ), and their unit cell parameters were estimated.     

Structural features of phases (Na<Subscript>0.5</Subscript>R<Subscript>0.5</Subscript>)MO<Subscript>4</Subscript> and (Na<Subscript>0.5</Subscript>R<Subscript>0.5</Subscript>)MO<Subscript>4</Subscript>:R′ (R = Gd,La; R′ = Er,Tm, Yb; M = W,Mo) of the scheelite family

The structural data for single crystals of (Na_0.5R_0.5)MO₄ and (Na_0.5R_0.5)MO₄:R′ (R = La, Gd; R′ = Er, Tm, Yb; M = W, Mo) grown by the Czochralski method were studied by X-ray diffraction and analyzed. The structural characteristics of these compounds depend on the sort of cations M and R. The formation of superstructures was found in the scheelite structure, and distortion of the scheelite structure depending on the composition and preparation conditions was established (with unit cell rotation by 45° and triclinic distortion of the scheelite structure for (Na_0.5Gd_0.5)WO₄:Tm, with doubled unit cell compared to the scheelite type structure for (Na_0.5Gd_0.5)WO₄ and (Na_0.5Gd_0.5)WO₄:Yb). In the case of overstoichiometric oxygen content in the crystal, the unit cell symmetry increases to space group I4₁/amd or (Na_0.5Gd_0.5)WO₄:Yb without considerable change in the cell parameters. On the basis of experimental data, a transformation scheme for the structures in the system Na ₂ ⁺ M⁶⁺O_4?-“R³⁺M⁵⁺O₄” was proposed.     

Geometric and electronic structure of an N,N′-ethylene-bis(salicylaldiminato) zinc(II) molecule,ZnO<Subscript>2</Subscript>N<Subscript>2</Subscript>C<Subscript>16</Subscript>H<Subscript>14</Subscript>

Gas electron diffraction at a temperature T of 641(5) K is used to study the structure of an N,N′-ethylenebis(salicylaldiminato) zinc(II) molecule, ZnO₂N₂C₁₆H₁₄, further Zn(salen). The structure of a gaseous Zn(salen) complex has C ₂ symmetry and is characterized by a substantial turn of two chelating fragments of the ligand with respect to each other, and also by a big difference in the length of coordination bonds: r _h1(Zn-O)=1.902(7) Å r _h1(Zn-N)= 2.027(7) Å. Results of the DFT/B3LYP calculation with 6-31G* and CEP,TZV basis sets of the molecule structure well agree with the experimental data. The electronic structure of Ni(salen), Cu(salen), Zn(salen), and Zn(acacen) molecules is considered.     

Manganese(II) 9-Molybdomanganate(IV), [Mn(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>]<Subscript>3</Subscript> · [MnMo<Subscript>9</Subscript>O<Subscript>32</Subscript>] · 2H<Subscript>2</Subscript>O: Synthesis,thermal analysis,IR spectra,and crystal structure

The [Mn(H₂O)₄]₃ · [MnMo₉O₃₂] · 2H₂O complex was synthesized and studied by X-ray diffraction, thermogravimetry, powder X-ray diffraction, and IR spectroscopy. The crystals are trigonal: space group R32, a = 14.811(2) Å, c = 14.232(2) Å, V = 2703.7(8) ų, M = 1848.5, Z = 3, ρ(calcd.) = 3.419 g/cm³.     

A theoretical investigation on the structures and stabilities of C<Subscript>60</Subscript>X<Subscript>18</Subscript> and C<Subscript>70</Subscript>X<Subscript>10</Subscript> (X = H,F, Cl,and Br)

A density functional theory study was performed on fullerene derivatives C₆₀X₁₈ and C₇₀X₁₀ (X = H, F, Cl, and Br). The calculated results show that the lowest energy isomers are IPR-satisfying for C₆₀X₁₈ (X = H, F, Cl, and Br). It is found that the addition patterns of X (X = Cl and Br) are different from those of X (X = H and F) for C₆₀, demonstrating that the stability of fullerene derivatives is partly attributed to the steric repulsion and electronegativity of added atoms. However, the lowest energy isomers are IPR-violating for C₇₀X₁₀ (X = H, F, and Cl), suggesting that many more fullerene derivatives may violate the isolated pentagon rule.     

Phase formation in Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-K<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MMoO<Subscript>4</Subscript> (M = Ca,Pb, Ba) systems and the crystal structure of α-KLiMoO<Subscript>4</Subscript>

Solid-phase interactions in Li₂MoO₄-K₂MoO₄-MMoO₄ (M = Ca, Pb, Ba) systems were studied, and the subsolidus regions of these systems were triangulated. The lead and barium systems were studied in a more detailed way to discover that, along KLiMoO₄-K₂M(MoO₄)₂ (M = Pb, Ba), KLiMoO₄-PbMoO₄, and Li₂MoO₄-K₂Ba(MoO₄)₂ quasi-binary sections, there are homogeneity regions reaching 6–11 mol % based on K₂M(MoO₄)₂ and lead molybdate. Triple molybdates are formed in none of the systems, which is verified by experiments on spontaneous crystallization from solution in melt. Crystallization experiments yielded crystals of potassium dimolybdate and simple and double molybdates from the boundary systems. The crystal structure was solved for a hexagonal KLiMoO₄ phase: (Na,K){ZnPO4}, a = 18.8838(7) Å, c = 8.9911(6)Å, Z = 24, space group P6₃, R = 0.065. The structure comprises a three-dimensional tridymite framework built by an alternation of corner-sharing LiO₄- and MoO₄ tetrahedra wherein voids are occupied by potassium cations.     

Exohedral Silicon Fullerenes: Si<Subscript>60</Subscript>Pn<Subscript>60</Subscript> and Si<Subscript>80</Subscript>Pn<Subscript>60</Subscript> (Pn = P,As, Sb and Bi)

Based on density functional theory (DFT) calculations, we predict that the icosahedral structures of the silicon fullerenes Si₆₀ and Si₈₀ can be stabilized by 12 exohedral pentagons of group V-A unit Pn₅ (Pn = P, As, Sb or Bi). The 12 pentagons can fully passivate the dangling bonds associated with 12 pentagonal Si₅ rings on the silicon fullerene cages, thereby resulting in stable exohedral silicon fullerenes Si₆₀Pn₆₀ and Si₈₀Pn₆₀. Properties of the eight Si₆₀Pn₆₀ and Si₈₀Pn₆₀ clusters, including harmonic vibrational frequencies, electron affinity (EA), the HOMO–LUMO gap and NICS values, are computed. We find that all eight Si₆₀Pn₆₀ and Si₈₀Pn₆₀ fullerenes possess relatively large HOMO–LUMO gaps, high electron affinities, and that the Si₆₀Pn₆₀ fullerenes exhibit weak aromaticity. Among eight clusters examined, the exohedral fullerene I _h-Si₆₀P₆₀ possesses the largest cohesive energy per atom. Ab initio molecular dynamics (AIMD) simulation is performed to demonstrate thermal stability of the hollow cage structure of Si₆₀P₆₀ at the room temperature.     

Concentration Space of Homogeneous Garnet in the System Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–(Y,Bi)<Subscript>3</Subscript>(Fe,Ga)<Subscript>5</Subscript>O<Subscript>12</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The concentration space of homogeneous garnet in the system Ga₂O₃–(Y, Bi)₃(Fe, Ga)₅O₁₂–Fe₂O₃ was determined by X-ray powder diffraction analysis. The obtained results expand the knowledge of the possible variations of cation ratios Y : Bi : Fe : Ga in garnet, which can be used for searching for and creating new stable magneto-optical materials.     

Synthesis,morphology, and activity of La<Subscript>1–x</Subscript>Ag<Subscript>x</Subscript>MnO<Subscript>3 ± y</Subscript> catalysts

La_1–xAg_xMnO_{3 ± y} (x = 0-0.3) mixed oxides have been synthesized by the pyrolysis of polymer–salt compositions using different organic compounds and different salt: organic compound ratios. The correlation between the reaction medium temperature during pyrolysis, the composition of the resulting oxide, and synthesis conditions has been investigated. The effect of these conditions on the character of the pyrolysis process, on the phase composition and microstructure of the resulting oxide particles and metallic silver, and on their mutual distribution is reported. The catalytic properties of the synthesized oxides in methane and soot oxidation are considered, and a correlation is established between the catalytic activity of the oxides and the synthesis conditions.     

Molecular geometries,electronic properties,and vibrational spectroscopic studies of endohedral metallofullerenes TM@C<Subscript>24</Subscript> and TM@C<Subscript>24</Subscript>H<Subscript>12</Subscript> (TM = Cr,Mo, and W)

Molecular geometries, electronic properties, and vibrational spectroscopies of TM@C₂₄ and TM@C₂₄H₁₂ (TM = Cr, Mo, and W) in their different spin configurations have been systematically investigated with the hybrid DFT-(U)B3PW91 functional. The results show that the TM atoms bind over the pentagon ring inside C₂₄ cage, and they move gradually toward the center of C₂₄ cage along with the increasing atomic radii. The most stable Mo@C₂₄H₁₂ and W@C₂₄H₁₂ are in their spin-triplet states. The analyses of dissociation energy and energy gap reveal that TM@C₂₄ (TM = Cr, Mo, and W) and Cr@C₂₄H₁₂ are not only thermodynamically stable, but also considerably stable kinetically. Meanwhile, natural population analyses tell us that the two cages act as electron acceptors, and the transferred charge from the W atom to C₂₄ cage is the largest in the endohedral metallofullerenes. Additionally, the vibrational frequencies and active infrared intensities may be used as evidence to characterize these unknown species.     

Preparation specifics and properties of AMn<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript> (А = Ca,Ce, and Sm) high-pressure phases

Perovskite-like phases AMn₃V₄O₁₂ (A = Ca, Ce, and Sm) were prepared under borothermic conditions (p = 7.0–9.0 GPa, T = 700–1100°C). Their X-ray diffraction structure (space group Im \(\bar 3\), Z = 2) was determined, and unit cell parameters were calculated: for CaMn₃V₄O₁₂: а = 7.40824(3) Å, for SmMn₃V₄O₁₂: а = 7.45280(8) Å, and for CeMn₃V₄O₁₂: а = 7.46965(4) Å. The temperature-dependent electrical resistivity (10–300 K) and magnetic susceptibility (2–300 K) of the prepared phases were studied.     

(Indenyl)iridacarborane (η<Superscript>5</Superscript>-indenyl)Ir(η-7,8-C<Subscript>2</Subscript>B<Subscript>9</Subscript>H<Subscript>11</Subscript>): synthesis,structure, and bonding

A reaction of iodide [(η⁵-indenyl)IrI₂]_n (1) with thallium dicarbollide Tl[Tl(η-7,8-C₂B₉H₁₁)] leads to (indenyl)iridacarborane (η⁵-indenyl)Ir(η-7,8-C₂B₉H₁₁) (2) in 32% yield. The X-ray diffraction study showed that in the structure of 2, the five-membered rings C₅ and C₂B₃ have a cisoid conformation, in which the bridgehead carbon atoms of the indenyl ligand are arranged opposite to the carborane cage carbon atoms. The DFT calculations showed that the Ir—indenyl bond in compound 2 is weaker than the Ir—Cp bond in the complex (η-7,8-C₂B₉H₁₁)IrCp.     

Ternary Systems NaHal–NaVO<Subscript>3</Subscript>–Na<Subscript>2</Subscript>CrO<Subscript>4</Subscript> (Hal = Cl,Br)

Phase equilibria in the ternary systems NaHal–NaVO₃–Na₂CrO₄ (Hal = Cl, Br) were studied. By differential thermal analysis, eutectic alloys were found at points with coordinates (14.0 mol % NaCl, 66.5 mol % NaVO3, 19.5 mol % Na₂CrO₄, 530°C) and (27.0 mol % NaBr, 47.5 mol % NaVO₃, 25.5 mol % Na₂CrO₄, 499°C). By differential scanning calorimetry, the specific enthalpies of melting of the eutectics were determined. X-ray powder diffraction analysis of the eutectic alloy in the system NaBr–NaVO₃–Na₂CrO₄ was made.     

Structure of a zinc(II) N,N’-ethylene-bis (acetylacetoniminate) molecule,ZnO<Subscript>2</Subscript>N<Subscript>2</Subscript>C<Subscript>12</Subscript>H<Subscript>18</Subscript>, according to gas electron diffraction data and quantum chemical calculations

Gas electron diffraction is used to study the structure of a zinc(II) N,N’-ethylene-bis(acetylacetoniminate) molecule, ZnO₂N₂C₁₂H₁₈, at a temperature T = 503(5) K. It is found that the molecule has the symmetry of the C₂ equilibrium configuration with a nonplanar structure of the ZnN₂O₂ coordination fragment and internuclear distances r_h1(Zn-O) of 1.958(13) ? and _h1(Zn-N) of 2.012(16) ?. Quantum chemical calculations by the DFT/B3LYP/CEP,TZV method gives the molecular structure consistent with that found in the experiment.     

[H<Subscript>4</Subscript>(4,4′-Bipy)<Subscript>3</Subscript>][Sc(OH)(H<Subscript>2</Subscript>O)<Subscript>5</Subscript>]<Subscript>2</Subscript>Cl<Subscript>8</Subscript>: Synthesis,structure, and solid-phase thermal transformation

The reaction of [Sc(OH)(H₂O)₅]₂Cl₄ · 2H₂O in isopropanol with 4,4′-Bipy in CHCl₃ produced a crystalline compound, which was identified as [H₄(4,4′-Bipy)₃][Sc(OH)(H₂O)₅]₂Cl₈ (I) by elemental analysis, IR spectra, and single-crystal X-ray diffraction. In the structure of compound I, the three protonated diimine molecules form a centrosymmetric trimer via N...N hydrogen bonds. The polyhedron around the Sc atom is an octahedron with one split vertex. The excursion of the Sc atom from the plane formed by the oxygen atoms (water molecules) toward the hydroxo bridges is 0.5 Å. The thermolysis of compound I generates ScCl₃, whereas the final decomposition product of the precursor dimer is ScOCl.