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.     

Specific features of phase transitions and the conduction of La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> oxide-ion conducting compound doped with vanadium

The X-ray powder analysis, calorimetric studies, and conductivity measurements of a series of ceramic La₂Mo_2−x V _x O _y specimens with different vanadium content are performed with the aim of following the dynamics of phase formation of the low-temperature α, high-temperature β, and metastable β _ms phases. At x ≥ 0.06, the cubic phase becomes stable and the monoclinic phase vanishes; therefore, the main α → β transition is suppressed. According to the data of differential thermal analyses, a weak thermal anomaly is observed in the range 450–470°C at x ≥ 0.06. This anomaly is indicative of the β _ms → β transition due to the conversion of the cubic phase with statically disordered oxygen atoms into the cubic phase with dynamic disorder. The conductivity of the high-temperature β phase obeys the Vogel-Tammann-Fulcher law.     

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.     

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.     

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.     

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.     

<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 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.     

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.     

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,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.     

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.     

Synthesis and Crystal Structures of Octahedral Sn(IV) Complexes Prepared from SnCl<Subscript>2</Subscript>·2H<Subscript>2</Subscript>O and 2-Hydroxyacetophenone (<Emphasis Type="Italic">S</Emphasis>-benzydithiocarbazate) Ligand (H<Subscript>2</Subscript>L)

Abstract  

Two coordination octahedral Sn(IV) complexes [Sn(L)₂] and cis-[SnCl₂(L)(dmso)], where H₂L is 2-hydroxyacetophenone (S-benzydithiocarbazate), were prepared and characterized by elemental analysis, IR, NMR (¹H, ¹³C), ¹¹⁹Sn M?ssbauer spectroscopies and X-ray diffraction techniques to investigate their structural properties. Both crystallize in the Monoclinic system, with parameters: a = 8.1905(3), b = 30.8811(15), c = 12.8959(7) ?, β = 94.465(3)° and Z = 4 for [Sn(L)₂] and a = 8.5247(2), b = 21.5445(7), c = 12.3706(3) ?, β = 96.932(2)° and Z = 4 for cis-[SnCl₂(L)(dmso)]. In both complexes, the Sn(IV) central atom is coordinated in a distorted octahedral geometry with the thiolate ligand (L²⁻) coordinated via O, N and S atoms. The ¹¹⁹Sn M?ssbauer spectroscopy of the complexes were studied and the results revealed that both complexes posses isomer shift (δ) and quadrupole splitting (Δ), which are almost the same.     

Sequence of phase transitions in PbHfO<Subscript>3</Subscript>

The temperature changes in the PbHfO₃ structure in the temperature range of 20 < t < 400°C have been studied by X-ray powder diffraction. The sequence of phase changes with an increase in temperature was found to be as follows: orthorhombic phase Pbam (O1), orthorhombic phase C2mm (O2), tetragonal phase P4mm (T), and cubic phase Pm3m (C). The C2mm and P4mm phases are ferroelectric, which is confirmed by measuring the dependences ɛ(t). The similarity of the transition pattern obtained with the known transition sequences for ferroelectric (barium titanate, potassium niobate, and lead titanate) and antiferroelectric (lead zirconate) oxides is analyzed.     

Effect of doping and heat treatment on the mechanical parameters of ZnSe<Subscript>(1 − <Emphasis Type="Italic">x</Emphasis>)</Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> crystals grown from the melt

The mechanical properties of crystals of ZnSe_{(1 − x)}Te _x (0 < x < 1.3 wt %) solid solutions are investigated using the indentation method. The breaking points of doped and undoped crystals are measured by the uniaxial compression method. It is revealed that the microhardness anisotropy coefficient for crystals with a tellurium dopant content of ∼0.3 wt % is equal to unity. A change in the tellurium content in the solid solutions from 0.2 to 1.3 wt % leads to a linear increase in the microhardness by 23%. The brittle strength of the ZnSe and ZnSe_{(1 − x)}Te _x crystals varies in a similar manner. It is demonstrated that heat treatment and the presence of interblock boundaries affect the ultimate strength and the cracking resistance of the ZnSe_{(1 − x)}Te _x crystals. This is an important factor which should be taken into account in mechanical treatment of the materials under investigation.     

Synthesis and Structure of Ba<Subscript>5</Subscript>(V<Subscript>2</Subscript>O<Subscript>7</Subscript>)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>

Abstract  A new barium chlorovanadate, Ba₅(V₂O₇)₂Cl₂, was isolated by a high-temperature (850 °C) reaction employing a CsCl/RbCl flux. The structure was determined by single crystal X-ray diffraction methods. This compound crystallizes in an orthorhombic crystal system, Pmmn (No. 59), with a = 11.558(2) ?, b = 15.164(3) ?, c = 10.023(2) ?, Z = 4 and V = 1756.7(6) ?³. The structure of Ba₅(V₂O₇)₂Cl₂ was determined by full-matrix, least-squares methods with R ₁ = 0.0398, wR ₂ = 0.1069 and GOF = 1.048 for all data. This new structure can be described as a composite lattice made up of mixed covalent and ionic moities. The extended framework is orchestrated by stacked [Ba(V₂O₇)Cl]³⁻ slabs that are interconnected by Ba²⁺ cations through Ba–O bonds to the [V₂O₇] units. The Ba²⁺ and Cl^- ions form BN-type “[BaCl]” sheets with pseudo-hexagonal windows that are centered by [V₂O₇]⁴⁻ pyrovanadate units. Graphical Abstract  The structure of a new chlorovanadate, Ba₅(V₂O₇)₂Cl₂, exhibits an interesting BN-type salt lattice that consists of an extended [BaCl] sheet containing pseudo-hexagonal windows that are centered by [V₂O₇] pyrovanadate units.      

Structural Analysis of the Phase Transitions of (NH<Subscript>4</Subscript>)<Subscript>4</Subscript>HgBr<Subscript>6</Subscript>

Abstract Single crystal diffraction and differential scanning calorimetry DSC techniques have been used to investigate the different phases of (NH₄)₄HgBr₆, tetrammonium mercury hexabromide, from room temperature to 120 K. Two anomalies in thermal behaviour were detected for this compound at 190 and 268 K, by DSC experiment. X-ray diffraction measurements confirm these anomalies. At room temperature the structure is tetragonal P4/mnc (No. 128) with lattice parameters a = b = 9.25560(8) ?; c = 8.8657(11) ?; V = 759.49(9) ?³ and Z = 2. At T = 250 K the structure is orthorhombic Pnnm with lattice parameters a = 8.8436(8) ?; b = 9.2191(8) ?; c = 9.2232(7) ?; V = 751.97(11) ?³ and Z = 2. Below approximately 200 K the structure is monoclinic P2₁/n (No. 14) with: a = 8.8080(9) ?; b = 9.1608(8) ?; c = 9.1498(8) ?; β = 90.230(7)°; V = 738.28(12) ?³ and Z = 2 (T = 120 K). The structure of (NH₄)₄HgBr₆ consists of isolated HgBr₆-octahedra in the whole temperature range which are slightly compressed in c-direction. The ammonium groups are located between the octahedra ensuring the stability of the structure by hydrogen bonding contacts: N–H···Br. The structural phase transformations are described by a rotation of the [HgBr₆]²⁻ octahedra around the c-axis, and this behaviour is attributed to an orientational disorder of ammonium groups. Index abstract Structural analysis of the phase transitions of (NH₄)₄HgBr₆; M. Loukil, A. Kabadou, I. Svoboda, A. Ben Salah and H. Fuess; The phase transformations in (NH₄)₄HgBr₆ are explained by large rotation of [HgBr₆]²⁻ octahedra around the c-axis.      

Structure of phases of the sillenite family in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript> system

X-ray diffraction studies of sillenite Bi₂₄V₂O₄₀ single crystals grown by the hydrothermal method are performed for a separate crystal and powdered crystals. It is found that the composition of the two specimens is described by the (Bi_{24 − x} ▭ _x )[Bi _y ³⁺V_1−y ⁵⁺]₂ O₄₀ general formula with completely populated oxygen sites but differs in the content of vacancies at the bismuth site (this was established for the first time) and the Bi: V ratio at the tetrahedral site. The structural models of all the vanadium-containing sillenites reported in the literature are considered, and the possibility that Bi atoms are located at the centers of BiO₄ tetrahedra is established.