Crystal structure and properties of polymeric hexaaqua-<Emphasis Type="Italic">hexakis</Emphasis>-(2-thiobarbiturato)-disamarium(III)

The structure (CIF file CCDC No. 1401886) of the hexaaqua-hexakis(2-thiobarbiturato)-disamarium [Sm₂(H₂O)₆(HTBA)₆] _n polymeric complex (I), where H₂ТВА is 2-thiobarbituric acid, is determined; its thermal decomposition and IR spectrum are studied. The crystals of I are monoclinic: a = 14.072(1) Å, b = 10.0842(6) Å, c = 15.323(1) Å, β = 110.408(2)°, V = 2037.9(2) ų, space group P2/n, Z = 2. All three independent thiobarbiturate anions HTBA^– coordinate to Sm³⁺ through oxygen atoms. To one of independent Sm³⁺ ions six (two terminal and four bridging) HTBA^– ions and two water molecules are coordinated; the second is bonded with four bridging HTBA^– and four water molecules, forming square antiprisms. The bridging HТВА–anions arrange antiprisms in layers. The structure is stabilized by hydrogen bonds and a π–π interaction between the HТВА^– ions. The topology of the polymer network of I is analyzed.     

Synthesis,Crystal Structure,and Magnetic Properties of the YbFeTi<Subscript>2</Subscript>O<Subscript>7</Subscript> Compound

We report on the synthesis conductions and results of experimental investigations of the crystal structure and magnetic properties of a new magnetic compound YbFeTi₂O₇. According to the X-ray diffractometry data, the crystal structure of the investigated compound is described by the rhombic space group Pcnb with unit cell parameters of a = 9.8115(1) Å, b = 13.5106(2) Å, and c = 7.31302(9) Å and atomic disordering in the distribution of iron ions Fe³⁺ over five structural sites. The magnetic measurements in the lowtemperature region revealed a kink in the temperature dependence of the magnetic moment and its dependence on the sample magnetic prehistory. The experimental results obtained suggest that with a decrease in temperature the sample passes from the paramagnetic state to the spin-glass-like magnetic state characterized by a freezing temperature of T _f = 4.5 K at the preferred antiferromagnetic exchange coupling in the sample spin system. The chemical pressure variation upon replacement of rare-earth ion R by Yb in the RFeTi₂O₇ system does not change the crystal lattice symmetry and magnetic state.     

Study of the Physical Properties and Electrocaloric Effect in the BaTiO3 Nano- and Microceramics

Physics of the Solid State - The specific heat, thermal expansion, permittivity, and electrocaloric effect in bulk of BaTiO3 (BT) samples in the form of nano- (nBT-500 nm) and micro- (mBT-1200 nm)...     

Heat capacity,structure, and <Emphasis Type="Italic">p-T</Emphasis> phase diagram of elpasolite (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>KMoO<Subscript>3</Subscript>F<Subscript>3</Subscript>

Thermophysical and structural studies of an (NH₄)₂KMoO₃F₃ crystal show that this crystal belongs to the family of elpasolites (space group \(Fm\bar 3m\)) and undergoes an order-disorder phase transition at T ₀ = 241.5 K. Under hydrostatic pressure, this phase transition splits into two consecutive transitions at the tricritical point with parameters T _tr = 232.5 K and p _tr=0.21 GPa. It was found that anomalous hysteresis and relaxation phenomena accompany the transitions from the cubic to both distorted phases. The results are analyzed taking into account the data on the phase transition in the related elpasolite (NH₄)₂KWO₃F₃.     

ChemInform Abstract: Structural Transformation Between Two Cubic Phases of (NH4)3SnF7.

Single crystals of (NH₄)₃SnF₇ are obtained from aqueous solutions of (NH₄)₂SnF₆ and excess NH₄F during solvent evaporation.     

Crystal structure of catena-(2-thiobarbiturato) dithallium(I)

By powder X-ray diffraction the crystal structure of catena-(2-thiobarbiturato)dithallium(I) C₄H₂N₂O₂STl₂ (C₄H₄N₂O₂S is 2-thiobarbituric acid, H₂TBA), Tl₂TBA, is determined. Crystallographic data for Tl₂TBA are as follows: a = 15.1039(3) Å, b = 12.0818(2) Å, c = 3.86455(6) Å, β = 97.203(1)°, V = 741.34(2) ų, space group P2₁/n, Z = 4. There are two non-equivalent thallium atoms in the structure. The Tl1 polyhedron is a distorted trigonal prism due to the shortened Tl-S contact (3.634 Å), and the Tl2 polyhedron is a distorted square antiprism.     

Structures of bis(2-thiobarbiturato-O)tetraaquamagnesium and catena-[(μ2-2-thiobarbiturato-O,O)(2-thiobarbiturato-O) bis(μ2-aqua)diaquastrontium] monohydrate

The crystal structures of bis(2-thiobarbiturato-O)tetraaquamagnesium Mg(H₂O)₄(HTBA-O)₂ I and catena-[(μ₂-2-thiobarbiturato-O,O)(2-thiobarbiturato-O)bis(μ₂-aqua)diaquastrontium] monohydrate catena-[Sr(μ₂-H₂O)₂(H₂O)₂(μ₂-HTBA-O,O)(HBTA-O)] _n · nH₂O (II), where H₂TBA is 2-thiobarbituric acid C₄H₄N₂O₂S, have been determined. Crystal data for a=6.7598(2) Å, b = 7.6060(2) Å, c = 8.5797(2) Å, α = 79.822(2)°, β = 76.622(1)°, γ = 69.124(1)°, V = 398.82(2) ų, space group P $\bar 1$ , Z = 1; for II: a = 20.8499(4) Å, b = 19.2649(5) Å, c = 4.14007(9) Å, β = 92.023(2)°, V = 1661.91(7) ų, space group P2₁/n, Z = 4. The Mg²⁺ ion in I is bonded to six O atoms of two HTBA^? ions and four water molecules that form a nearly regular octahedron. Each Sr²⁺ ion in II is coordinated to three oxygen atoms of three HTBA^? ions and six water molecules that form an almost ideal tricapped trigonal prism. These polyhedra share edges to form infinite chains. Intermolecular hydrogen bonds create layered structures of I and II.     

Polymeric lithium(I) diaquabarbiturate: Crystal structure

The lithium(I) catena-diaquabarbiturate complex [Li(H₂O)₂(HBA–O,O′)] _n (I), where Н₂ВА is barbituric acid, has been structurally characterized by X-ray diffraction (CIF file CCDC no. 1447689), and its thermal decomposition and IR spectrum have been studied. Crystals of complex I are monoclinic, a = 6.4306(7) Å, b = 16.720(1) Å, c = 7.1732(8) Å, β = 108.253(4)°, V = 732.5(1) ų, space group P2₁/c, and Z = 4. One independent μ₂-bridging HBA^– ligand is coordinated to two Li(I) ions via the two oxygen atoms of C₄₍₆₎=O carbonyl groups. Each Li⁺ ion is linked with two μ₂-HBA^– ions and two terminal water molecules at tetrahedron vertices. μ₂-HBA^– ions link tetrahedra into a chain. The structure is stabilized by multiple hydrogen bonds and π–π-interaction between HBA^–. The shift of ν(C=O) vibration bands in the IR spectrum of complex I in comparison with Н₂ВА towards lower frequencies agrees with the coordination of HBA^– via oxygen atoms. The dehydration of complex I occurs in two stages in the regions of 100–150 and 150–240°C.     

Processes of ordering of structural elements, critical and noncritical parameters of phase transitions in the (NH4)3WO3F3 crystal

The structure of the low-temperature triclinic phase of the (NH₄)₃WO₃F₃ crystal has been determined and the structure of the cubic phase of this crystal has been refined from data of an X-ray diffraction experiment performed for a powder sample. The profile and structural parameters have been refined according to the procedure implemented in the DDM program. The results obtained have been discussed with invoking the group-theoretical analysis of the complete order parameter condensate, which takes into account the critical and noncritical atomic orderings and allows one to interpret the obtained experimental data. It has been found that the symmetry transformation in the crystal can be schematically represented in the following form: Fm[`3]m(Z = 4) ? P[`1](Z = 1) ? P[`1](Z = 6)Fm\bar 3m(Z = 4) \to P\bar 1(Z = 1) \to P\bar 1(Z = 6). This transformation is accompanied by the complete ordering of WO₃F₃ polyhedra and the displacement of NH₄ ions.     

Dielectric and electrical properties of polymorphic bismuth pyrostannate Bi2Sn2O7

The Bi₂Sn₂O₇ compound existing simultaneously in two polymorphic modifications, namely, orthorhombic and cubic, has been synthesized for the first time by solid-phase synthesis. The dielectric and electrical properties of the compound have been studied in the temperature range 100 K < T < 500 K. Anomalies in the temperature dependences of the electrical resistivity and the permittivity (imaginary and real parts) have been found at both low and high temperatures. These features are explained in terms of the model of martensitic phase transitions.