Synthesis and phase transitions of oxide-ion conducting compound La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> doped with alkaline metals

The specific features of synthesis, polymorthism, and electric conductivity of oxide-ion conducting compounds La_{2 − x} Me _x Mo₂O_{9 − y} , where Me = Na, K, Rb, or Cs, have been studied. Ceramic samples were obtained by solid-state synthesis in the temperature range of 960–1100°C. The regions where solid solutions exist have been found to depend on the temperature of the sample firing. According to the calorimetric and electrophysical data, the phase transition from the monoclinic phase (α) to the cubic phase (β) in samples doped with potassium and rubidium disappears at x = 0.02 and 0.04, respectively. In these cases the only transition from the cubic β _ms phase to the high-temperature cubic β phase is observed near 450°C. Doping with sodium and cesium does not suppress the α → β phase transition.     

Structure and properties of antimony-doped lanthanum molybdate La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript>

Polycrystalline samples of the composition La₂Mo_{2 − x} Sb _x O_{9 − y} , where 0 ≤ x ≤ 0.05, were prepared by solid-phase synthesis. Single crystals of La₂Mo_1.96Sb_0.04O_8.17 were obtained by spontaneous crystallization from flux. The structure of the metastable β _ms phase of this compound was determined at room temperature by X-ray diffraction. It was found that the La, Mo, and O1 atoms are displaced from the threefold axis on which they are located in the high-temperature β phase. It was shown that molybdenum atoms in the crystal structure are partially replaced by antimony atoms, which are located on the threefold axis. In antimony-doped crystals, lanthanum atoms partially return to the site on the threefold axis and the coordination environment of molybdenum cations becomes more ordered, thus facilitating the stabilization of the cubic phase at room temperature. Calorimetric measurements (DSC) showed that the introduction of Sb as the dopant into the La₂Mo₂O₉ structure leads to a decrease in the temperature of the α → β phase transition from 570 to 520°C and to the partial suppression of this transition. The temperature behavior of the conductivity confirms the DSC data. Thus, doping with Sb contributes to the stabilization of the cubic phase at room temperature.     

Crystal structure of La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> single crystals doped with bismuth

Precision X-ray diffraction studies of La_{2 − x} Bi _x Mo₂O₉ (x = 0.04, 0.06, and 0.18) single crystals are performed. It is found that in the compounds doped with bismuth, analogously with the structure of the metastable β_ms phase of pure La₂Mo₂O₉ (LM), the La, Mo1, and O1 atoms deviate from the threefold axis on which they are located in the high-temperature β phase. It is shown that bismuth atoms substitute for part of lanthanum atoms and occupy a position at the threefold axis in the neighborhood of the split lanthanum position. The implantation of bismuth atoms in the LM structure results in the return of a part of the molybdenum atoms to the position at the threefold axis. The occupancy of this position is equal to the occupancy of the bismuth atomic position.     

Invar effect in PbFe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>O<Subscript>3</Subscript> ceramics

High-density lead ferroniobate PbFe_1/2Nb_1/2O₃ (PFN) is prepared by conventional ceramic technology. Its structural properties are studied in a wide temperature range (293 ≤ T ≤ 973 K). The following chain of phase transitions is established in the vicinity of the transition to the polar phase: Rh (rhombohedral phase) (T < 363 K) → Psc (pseudo-cubic phase) (363 < T < 387 K) → C (cubic phase) (T > 387 K). The paraelectric range contains five ranges of constant unit-cell volume (invar effect): I (387 ≤ T ≤ 413 K), II (433 ≤ T ≤ 463 K), III (553 ≤ T ≤ 613 K), IV (743 ≤ T ≤ 773 K), and V (798 ≤ T ≤ 823 K). It is shown that the anomalous behavior of the PFN dielectric characteristics above the Curie temperature, which was revealed previously, is associated with the specific features of its real (defect) structure, which is caused by the crystal-chemical specificity of the main structure-forming agents: α-Fe₂O₃ and α_ht-Nb₂O₅.     

Hydrothermal Synthesis and Structure of Fe<Subscript>6.36</Subscript>Mn<Subscript>0.64</Subscript>(PO<Subscript>3</Subscript>(OH))<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Abstract  

Single crystals of iron and manganese phosphate Fe_6.36Mn_0.64(PO₃(OH))₄(PO₄)₂ was synthesized by hydrothermal method. The compound crystallizes in the Fe₇(PO₄)₆ structure type and is isotypic with the solid solution \textM_{7 - \textx} \textM_\textx^￠ ( \textHPO₄ )₄ ( \textPO₄ )₂ {\text{M}}_{{7 - {\text{x}}}} {\text{M}}_{\text{x}}^{\prime} \left( {{\text{HPO}}_{4} } \right)_{4} \left( {{\text{PO}}_{4} } \right)_{2} where M is Fe, Co, Mg, Mn. The compound is triclinic, P-1, a = 6.571(5), b = 7.993(3), c = 9.547(2) Ǻ, α = 103.97(1)°, β = 109.29(2)°, γ = 101.57(3)°. The structure is based on a three-dimensional framework of distorted edge-sharing MO₆ and MO₅ polyhedra, forming infinite chains, which are interlinked by corner-sharing with PO₄ tetrahedra. The formula unit is centrosymmetric, with all atoms in general positions except for one Fe atom, which has site symmetry −1.     

Influence of structural ordering on ion transport in BiO<Subscript>0.5</Subscript>F<Subscript>2.0</Subscript> bismuth oxyfluoride

The influence of structural defect ordering on ionic conductivity (σ) in the cubic (fluorite) modification of BiO_0.5F_2.0 oxyfluoride has been investigated. Upon cooling, the disordered fluorite BiO_0.5F_2.0 phase undergoes a reversible transition to an ordered form. This transition manifests itself as a jump in the temperature dependence σ(T) near 583 ± 6 K. The ordering of structural defects deteriorates the characteristics of ion transport in BiO_0.5F_2.0. At 500 K, the σ value for the ordered phase is 1 × 10⁻⁴ S/cm, whereas an extrapolation to this temperature for the disordered phase gives σ = 4 × 10⁻⁴ S/cm.     

<Emphasis Type="Italic">Trans</Emphasis>-dibromodioxodimethylformamide molybdenum(VI) MoO<Subscript>2</Subscript>Br<Subscript>2</Subscript>(OCHNMe<Subscript>2</Subscript>)<Subscript>2</Subscript>

The molecular structure of trans-dibromodioxodimethylformamide molybdenum(VI), MoO₂Br₂(OCHNMe₂)₂ has been determined. Crystal data: Triclinic, P-1, a = 12.3005(2), b = 15.8763(4), c = 21.1653(6) ?, α = 71.992(1)°, β = 88.966(2)°, γ = 89.999(1)°, V = 3930.1(2) ?, Z = 12. Trans-dibromodioxodimethylformamide molybdenum(VI) was obtained by the reaction of sodium molybdate, HBr and dimethylformamide and was characterized by IR, and ¹H NMR spectroscopy and elemental analysis.     

Synthesis and properties of zirconium-doped RbTiOPO<Subscript>4</Subscript> single crystals

Single crystals of the solid solutions RbTi_{1 ? x} Zr _x OPO₄ (0.015 < x < 0.034) were grown and their physical properties were studied. In the presence of zirconium in the crystals with the maximum content x = 0.034, the ferroelectric phase transition and the high-temperature transition from the orthorhombic to the cubic phase are shifted to lower temperatures by 100 and 50°C, respectively. In the temperature range from 700°C to room temperature, the conductivity of doped crystals decreases compared to that of the undoped crystals. It is of particular interest that the intensity of the second-harmonic generation of the doped crystals is substantially higher than that of RbTiOPO₄.     

Investigation of the structural conditionality for changes in physical properties of K<Subscript>3</Subscript>H(SO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystals

With the aim of elucidating the nature of anomalies in the physical properties of K₃H(SO₄)₂ crystals that arise as the temperature grows, the dielectric and optical properties of the crystals are studied, an X-ray diffraction analysis of single-crystal and polycrystalline specimens are performed, and the morphology and chemical composition are studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. As a result of the studies performed, a phase transition from the phase with the monoclinic symmetry (space group C2/c) to the phase with the trigonal symmetry (space group R $ \bar 3 $ \bar 3 m) is found in a number of K₃H(SO₄)₂ specimens at a temperature of ≈457 K, the responsibility of the dynamically disordered hydrogen-bond system for the rise of high proton conductivity in the high-temperature phases of the crystals of this family is confirmed, and data on the solid-phase reactions proceeding at high temperatures are obtained.     

Synthesis,Spectrum Properties,and Crystal Structure of a New Pentaborate,Na<Subscript>2.18</Subscript>K<Subscript>0.82</Subscript>SrB<Subscript>5</Subscript>O<Subscript>10</Subscript>

Abstract  

A novel quaternary borate, Na_2.18K_0.82SrB₅O₁₀, has been prepared by high-temperature solution reaction below 800 °C. Single-crystal XRD analyses showed that it crystallizes in the triclinic P[`1] P\bar{1} group with a = 7.3900(15) ?, b = 7.6490(15) ?, c = 9.773(2) ?, α = 79.31(2)°, β = 70.85(2)°, γ = 62.09(1)°, Z = 2. The basic structural unit in Na_2.18K_0.82SrB₅O₁₀ is a double ring [B₅O₁₀]⁵⁻ composed of one BO₄ tetrahedron and four BO₃ triangles. The [B₅O₁₀]⁵⁻ groups are arranged around crystallographic centers of symmetry to form [B₁₀O₂₀]¹⁰⁻ columns that are held together by Na⁺, K⁺/Na⁺, and Sr²⁺ cations via electrostatic interactions. The IR spectrum further confirmed the presence of both BO₃ and BO₄ groups. UV–vis diffuse reflectance spectrum showed a band gap of about 3.80 eV. Solid-state fluorescence spectrum exhibited the maximum emission peak at around 337.6 nm.     

X-ray diffraction study of (TlInSe<Subscript>2</Subscript>)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(TlGaTe<Subscript>2</Subscript>)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> crystal system

The crystallographic and dynamic characteristics of TlInSe₂ and TlGaTe₂ crystals have been studied by X-ray diffraction in the temperature range of 85–320 K. The temperature dependences of the unit-cell parameters a of TlInSe₂ and TlGaTe₂ crystals, as well as their coefficients of thermal expansion along the [100] direction, are determined. The concentration dependences of the unit-cell parameters a and c for (TlInSe₂)_{1 − x} (TlGaTe₂) _x crystals are measured. Anomalies are found in the temperature dependences of the unit-cell parameters a and, correspondingly, the coefficient of thermal expansion, indicating the existence of phase transitions in TlInSe₂ and TlGaTe₂ crystals.     

Synthesis and crystal structure of anhydrous copper suberate: [Cu<Subscript>2</Subscript>(OOC-(CH<Subscript>2</Subscript>)<Subscript>6</Subscript> -COO)<Subscript>2</Subscript>]

The title compound [Cu₂(OOC-(CH₂)₆-COO)₂] was synthesized and its crystal structure has been determined by single crystal X-ray diffraction methods. The complex crystallizes in the triclinic space group P-1 with a=5.1077(5) ?, b=8.362(2) ?, c=11.378(2) ?, α=93.773(6)°, β=97.587(9)°, γ=90.493(’9)° and D _cal=1.629 mg/m³ for Z=1.  The structure is polymeric and consists of discrete anhydrous centrosymmetric binuclear units [Cu₂(OOC-(CH₂)₆-COO)₂]. The two copper(II) centres bridged by the suberate groups in a syn-syn conformation, are in pentacoordinated distorted square-pyramidal coordination environment, with an intramolecular Cu–Cu distance of 2.5793(10) ?. Each binuclear unit, related to the next through μ_oxo bridges with a Cuμ_oxo–Cuμ_oxo separation of 3.2326(10)?, defines infinite chains of one-edge sharing CuO₅ square pyramid.     

Reflection spectra of NaClO<Subscript>3</Subscript>, NaBrO<Subscript>3</Subscript>, and LiIO<Subscript>3</Subscript> gyrotropic crystals in the vacuum UV region

The reflection spectra in the fundamental-absorption region, 5–25 eV (250–40 nm), of optically active crystals with cubic symmetry (NaClO₃, NaBrO₃) and uniaxial optically active crystal (LiIO₃) have been investigated. It is shown that the reflection spectra of cubic crystals have a similar structure, which is determined by the electronic transitions in the XO₃ group. The comparison of these spectra with the corresponding spectrum of lithium iodide made it possible to determine the type of transition in the spectra of cubic crystals. Using the projection operator method, it was shown that the sign of optical rotation of cubic crystals with symmetry T is independent of the screw axis sign. Possible reasons for the unprecedentedy large optical rotation of lithium iodide crystal in the optical axis direction are considered.     

Crystal Structure of [Zn(2-Bromobenzoato)<Subscript>2</Subscript>]<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> and [Zn(2-Bromobenzoato)<Subscript>2</Subscript>(<Emphasis Type="Italic">N</Emphasis>-Methylnicotinamide)]<Subscript>2</Subscript>

Abstract  

The syntheses and structural characterizations of two novel 2-bromobenzoatozinc(II) complexes—[Zn(2-BrC₆H₄COO)₂] _n (I) and [Zn(2-BrC₆H₄COO)₂(mnad)]₂ (II), where mnad is N-methylnicotinamide are reported. Compound (I) crystallized with a monoclinic lattice (space group P2₁/c) and is polymeric in solid state. Its cell parameters are: a = 7.37220(10) Å, b = 19.9639(3) Å, c = 30.2756(5) Å, β = 94.7510(7)°, V = 4440.59(12) ų, Z = 4. The coordination environments of all zinc atoms are distorted tetrahedra built from four carboxylate oxygen atoms coming from four 2-bromobenzoato ligands. Compound (II) crystallized with a monoclinic lattice (space group P2₁/c) with a = 11.7488(2) Å, b = 20.3683(3) Å, c = 9.30130(10) Å, β = 100.3941(11)°, V = 2189.30(5) ų, Z = 2. This dimeric molecule features a paddle-wheel [Zn₂O₈] cage in solid state; the coordination environment of the central atom is square pyramidal consisting of four carboxylate oxygen atoms and the pyridine N atom of the mnad ligand.     

Synthesis,Structure and DNA-Binding Studies of Oxamido-Bridged Binuclear Copper(II) Complex: [Cu<Subscript>2</Subscript>(heap)](bipy)(ClO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Abstract  

A new μ-oxamido-bridged copper(II)–copper(II) binuclear complex with formula of [Cu₂(heap)](bipy)(ClO₄)₂, where H₂heap and bipy are N,N′-bis(N-hydroxyethylaminopropyl)-oxamide and 4,4′-bipyridine, respectively, has been synthesized and characterized by elemental analyses, molar conductivity measurement, IR and electronic spectra studies, and single-crystal X-ray diffraction. The single-crystal X-ray analysis reveals that the complex has two embedded inversion centers at the mid-points of the C6–C6ⁱ bond of the oxamido group and the C7–C7ⁱⁱ bond of the 4,4′-bipyridine, respectively [symmetry code: (i) 2−x, 1−y, 1−z; (ii) =2−x, −y, 1−z]. Copper(II) atom is in a square-planar coordination geometry. The Cu···Cu separation through the oxamido birdge is 5.1430(8) ?. The bridging ligand (heap²⁻) adopts a bis-tetradentate trans conformation. A one-dimensional hydrogen bonding supramolecular structure parallel to the [2 1 0] direction is found in the crystal. The interaction of the binuclear copper(II) complex with herring sperm DNA (HS-DNA) was investigated by using absorption and emission spectra, electrochemical techniques and viscometry. The results suggest that the binuclear copper(II) complex interacts with HS-DNA by electrostatic interaction with intrinsic binding constant of 1.54 × 10⁴ M⁻¹.     

The synthesis and structure of a novel alternating 1-D cobalt coordination polymer [Co(2,5-PDC)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>Co(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>]·4H<Subscript>2</Subscript>O

A novel cobalt complex [Co(2,5-PDC)₂(H₂O)₂Co(H₂O)₄]·4H₂O (2,5-PDCH₂ = 2,5-pyridinedicarboxylic acid) was synthesized and its crystal structure has been determined by X-ray diffraction. The crystallographic data are: triclinic P−1, a = 7.112(2) ?, b = 8.939(3) ?, c = 9.719(3) ?, α = 91.153(5)°, β = 101.136(5)°, γ = 108.001(4)°, V = 574.4(3) ?³, Z = 1. The compound [Co(2,5-PDC)₂(H₂O)₂Co(H₂O)₄]·4H₂O exhibits a novel one-dimensional network constructed from the interconnection of Co(2,5-PDC)₂(H₂O)₂ and Co(H₂O)₄, in which two kinds of six-coordinated Co(II) atoms have both octahedral coordination environments. Each 2,5-PDC anion connects two different coordinated cobalt ions alternately in an one-dimensional chain. The zigzag 1D alternating chains are linked by extensive hydrogen bonds to form a three-dimensional (3D) supramolecular structure, in which uncoordinated solvate molecules act as space filling particles. Supplementary data CCDC-264249 contains the supplementary crystallographic data for this paper. Copies of this information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: t44–1223–336033; e-mail: deposit@ccdc.cam.ac.uk or ) or also available from the author Xiaoqing Wang.     

The crystal and molecular structure of a trifluoroacetylacetonate complex of scandium,Sc(CH<Subscript>3</Subscript>COCHCOCF<Subscript>3</Subscript>)<Subscript>3</Subscript>

The crystal and molecular structure of Sc(CH₃COCHCOCF₃)₃ has been determined by X-ray diffraction. The compound crystallizes as pure mer-isomer in the orthorhombic space group Pbca with lattice parameters a=15.166(8) ?, b=13.560(7) ?, c=19.327(10) ?, α=β=γ=90°, V=3974(4) ?³, Z=8. The complex at 100 K is partially disordered in the crystal structure in an approximate 5:1 ratio with 83% fluorine population at C-11 and 17% at C-15. NMR data is compared to that previously reported.     

Structural Studies of (Pyridine)<Subscript>3</Subscript>ZnFe(CO)<Subscript>4</Subscript> and (Pyridine)(Neocuproin)CdFe(CO)<Subscript>4</Subscript>

Abstract  

The structure of the previously reported (py)₃ZnFe(CO)₄ (py = pyridine) has been determined, confirming the monomeric nature of this species. The complex has average Zn–N and Zn–Fe bond lengths of 2.0970(7) and 2.4017(3) ?, and features a coordination geometry about Fe which is intermediate between trigonal bipyramidal and face monocapped tetrahedral. The space group is P2₁/c, with a = 8.22080(10) ?, b = 16.1668(3) ?, c = 15.4669(3) ?, β = 102.5869(11)°, V = 2006.21(6) ?³, D_calc. = 1.558 g/cm³ at 150(1) K. A monomeric cadmium analogue, (pyridine)(neocuproin)CdFe(CO)₄, has also been synthesized, and found to possess a similar geometry, with average Cd–N and Cd–Fe bond lengths of 2.352(2) and 2.5380(5) ?. The space group is P[`1] P\overline{1} with a = 10.8900(2) ?, b = 11.3042(3) ?, c = 15.5488(4) ?, α = 85.1251(10)°, β = 84.3468(14)°, γ = 72.0377(15)°, V = 1808.93(7) ?³, D_calc. = 1.478 g/cm³ at 150(1) K.     

Synthesis and Electrical Properties of a Fluorite-Like Nd<Subscript>5</Subscript>Mo<Subscript>3</Subscript>O<Subscript>16</Subscript> Compound with Partial Substitution of Molybdenum by Tungsten,Niobium, or Vanadium

The phase formation of Nd₅Mo_{3 – x}W _x O_16.5, Nd₅Mo_{3 – x}Nb _x O_{16.5 – х/2}, and Nd₅Mo_{3 – x}V _x O_{16.5 – х/2} solid solutions based on a fluorite-like Nd₅Mo₃O_16.5 compound (mixed conductor with interstitial oxygen conductivity) has been studied. The electrical conductivity of doped compounds obeys the Arrhenius law and, at a low impurity content, is as high as 0.03–0.08 S/cm at 800°C. Substitution of Mo⁶⁺ cations by V⁵⁺ and Nb⁵⁺ cations reduces the interstitial oxygen content, which causes a decrease in the solid-solution electrical conductivity by 1–2 orders of magnitude and a decrease in the cubic unit-cell parameter. A wide diffuse anomaly with a maximum of about 1500–4000 has been observed in the temperature dependence of the permittivity for all single-crystal and polycrystalline samples in the range of 300–900°C.     

A 2D Network in Co-Crystal (1:1) Based on <Emphasis Type="Italic">trans</Emphasis>-[PtBr<Subscript>2</Subscript>(Acetoxime)<Subscript>2</Subscript>] and 18-Crown-6

Abstract  

A 1:1 co-crystal of trans-[PtBr₂(acetoxime)₂] and 18-crown-6 has been obtained by a slow-evaporation of the equimolar mixture of trans-[PtBr₂(acetoxime)₂] and the crown ether. The compound crystallizes in the triclinic space group P [`1] P\,\bar{1} , with unit cell parameters a = 7.4765(2) Å, b = 9.5044(2) Å, c = 10.1591(3) Å, α = 83.687(1)°, β = 70.847(1)°, γ = 79.773(1)°, Z = 1. trans-[PtBr₂(acetoxime)₂] is assembled with 18-crown-6 into a 2D network structure by interactions between the oxygen atoms of 18-crown-6 and the hydroxylic and methyl hydrogen atoms of the oxime ligands.