Neutron diffraction study of UO2SeO4 · 2D2O

A powdered sample of deuterated uranyl selenate dihydrate UO₂SeO₄ · 2D₂O is studied by neutron diffraction. This compound crystallizes in monoclinic space group P2₁/c; a = 6.974(1) Å, b= 8.289(2) Å, c = 11.664(2) Å, β=92.319(6)°, Z = 4, R _f = 3.14, R _I = 5.53, gC² = 2.82. The main structural units of the compound are [UO₂SeO₄(D₂O)₂] chains propagating along [100]. These chains are linked into a framework group (A = UO ₂ ²⁺ , T³ = SeO ₄ ^2? , and M¹ = D₂O) of uranyl complexes. These chains are linked into a framework by a system of hydrogen bonds formed by water hydrogen atoms of one chain and uranyl oxygen atoms of another.     

A preparatory and X-ray diffraction study of the SrCl2NdCl3 system

The SrCl₂NdCl₃ system was examined over the full composition range by the Guinier powder X-ray diffraction technique. A solid solution, Sr_(1−x)Nd_xCl_(2+x), was found for the composition region 0 < x < 0.18. Beyond the solid solution region two intermediate chloride phases were identified: Sr_0.80Nd_0.20Cl_2.20 (Sr₄NdCl₁₁) and Sr_0.643Nd_0.357Cl_2.357 (Sr₉Nd₅Cl₃₃). Orthorhombic Sr₄NdCl₁₁ is isostructural with vernier-type Sr₄DyCl₁₁; lattice parameters are a = 7.230(5); b = 35.292(18), and c = 6.826(4)Å. The phase Sr₉Nd₅Cl₃₃ exhibits hexagonal symmetry with lattice parameters a = 12.908(6) and c = 24.823(10), Å and is isostructural with Nd₁₄Cl₃₃.     

Effect of substituting6Li for7Li on ionic conductivity of α-Li3BO3

The ionic conductivity of γ-Li₃BO₃ is measured in wide intervals of temperatures and⁷Li to⁶Li ratios. It is found that the conductivity and activation energy vary nonmonotonically with variations in concentrations of the two isotopes; the concentration dependence of electroconductivity has a minimum, and that of the activation energy has a maximum at a⁷Li :⁶Li ratio of about 50 : 50 at. %; and the activation energy for conduction by⁶Li exceeds that by⁷Li     

Neutron diffraction study of Na2UO2(C2O4)2 · 5D2O

A sample of Na₂UO₂(C₂O₄)₂ · 5D₂O (I) was studied by powder neutron diffraction. The compound crystallizes in the triclinic system, space group P1, unit cell parameters: a = 6.934(1) ?, b = 7.566(1) ?, c = 15.409(2) ?, ?? = 94.720(6)°, ?? = 96.281(6)°, ?? = 111.765(5)°, Z = 2, R _F = 5.35, R _I = 6.73 and ??² = 2.89. The hydrogen bonds and non-valence contacts involved in the formation and binding of the {Na₂[UO₂(C₂O₄)₂(D₂O)](D₂O)₄} layers in I were analyzed using the Voronoi-Dirichlet polyhedra.     

LiO Raman Bands of 6Li2CO3 and 7Li2CO3

The Raman spectra of polycrystalline ⁶Li₂CO₃ have been recorded in the frequency region from 600 to 300 cm⁻¹. Four very weak bands have been observed for each compound the isotopic frequency shifts are reported. The results have been compared with those from the i.r. spectra for the LiO₄ tetrahedra.     

Electronic Structure and Chemical Bonding in Monoclinic and Cubic Li2-xHxTiO3 (0≤ x ≤ 2)

The linear muffintin orbitals method in a tight binding approximation and extended Huckel theory are used to study the electronic structure and chemical bonding of lithium titanate (Li₂TiO₃) and its protonated analogs (Li_1.75H_0.25TiO₃ and H₂TiO₃). The effect of protons on electron spectrum characteristics and bond strength are investigated for the monoclinic and cubic phases of lithium titanate. Phase stability is evaluated by cohesion energy calculations.     

Neutron diffraction study of the HF adducts containing a hydrogen bond F-H?O

Single-crystal structures of HF adducts of acid salts CsH₂PO₃·HF, KH₂PO₄·HF, and CsH₂PO₄·HF were determined by neutron diffraction using the Laue method. In the crystals, HF molecules are connected to anions by means of new type of hydrogen bonds, F-H?O, which are significantly shorter (F?O distances 2.356-2.386(3) Å) than strong O-H?O or O-H?F hydrogen bonds. The H-F distances in the structures of these adducts, 1.020-1.027(5) Å, are compared with those in crystalline HF and hydrofluoride anions.     

Pressure-induced phase transition of Fe2TiO4: X-ray diffraction and Mössbauer spectroscopy

X-ray diffraction and Mössbauer spectroscopy were employed to investigate structural stability of Fe₂TiO₄ under high pressure. Measurements were performed up to about 24 GPa at room temperature using diamond anvil cell. Experimental results demonstrate that Fe₂TiO₄ undergoes a series of phase transitions from cubic (Fd3?m) to tetragonal (I4₁/amd) at 8.7 GPa, and then to orthorhombic structure (Cmcm) at 16.0 GPa. The high-pressure phase (Cmcm) of Fe₂TiO₄ is kept on decompression to ambient pressure. In all polymorphs of Fe₂TiO₄, iron cations present a high-spin ferrous property without electric charge exchange with titanium cations at high pressure supported by Mössbauer evidences.     

X-ray diffraction and electron microscope study of the Bi2S3PbBi2S4 system

An electron microscope and X-ray diffraction phase analytical study of the Bi₂S₃-galenobismutite (∼PbBi₂S₄) system has been made on samples rapidly quenched from the melt and samples prepared by sintering Bi₂S₃ and PbS at a temperature of 996 K, 10 K below the eutectic temperature. Five well-ordered phases were found, Bi₂S₃, galenobismutite, and three twinned phases, V-1, V-2, and V-3. The X-ray powder data of these materials are given as well as the refined lattice parameters. Electron microscope examination of the samples using a technique involving slight misalignment of the crystal fragments allowed the structures of disordered materials in the phase V region to be determined.     

Synthesis of YbBr2 and YbCl2 and an x-ray diffraction study of the system YbBr2YbCl2

Ytterbium dichloride was prepared in pure form by the oxidation of elemental ytterbium by ZnCl₂ with subsequent removal of the zinc impurities by sublimation. Ytterbium dibromide in the orthorhombic SrI₂-type structural form was prepared in a sealed tantalum container by reduction of the tribromide with elemental ytterbium at a temperature not exceeding 960°C for 15 min. The dihalides, mixed intimately in appropriate molar ratios in a glove-box and contained in pyrolytic graphite boats, were melted under vacuum. These two halides form a solid solution with the SrI₂-type structure. Lattice parameters are reported as a function of composition.     

Structure of β-SrRh2O4 from X-ray and neutron powder diffraction

β-SrRh₂O₄, a novel high temperature phase, is prepared as black powder by solid state reaction of SrCO₃ with Rh in air. The compound crystallises in the space group P63c, Z = 1, with a = 3.0626(2) Å and c = 11.3996(7) Å. The structure consists of Cd1₂-type layers of edge sharing RhO₆ octahedra with an AABB oxygen layer sequence. Strontium is found in partial occupation of both available interlayer sites, in trigonal prismatic coordination.     

A theoretical study of hydrogen- and lithium-bonded complexes of F-H∕Li and Cl-H∕Li with NF3, NH3, and NH2(CH3)

Hydrogen- and lithium-bonded complexes of A-H∕Li (A = F, Cl) with the amine analogues NF(3), NH(3), and NH(2)(CH(3)) were studied at the MP2∕6-311++G(d,p) level of theory. Bond extensions and redshifts were obtained for the H-bonded complexes, while bond extensions and blueshifts were obtained for the Li-bonded species. The variation of these and other properties with the basicity of the amines was investigated and rationalized by comparing the ab initio results with predictions from a model derived from perturbation theory.     

Synthesis and study of lithium triuranate Li2U3O10 · 6H2O

Li₂U₃O₁₀ · 6H₂O crystal hydrate was synthesized by the reaction between synthetic schoepite UO₃ · 2.25H₂O and aqueous lithium nitrate solution under hydrothermal conditions at 200°C. The composition and structure of the obtained compound were established, and its dehydration and thermal decomposition were studied, by chemical analysis, X-ray diffraction, IR spectroscopy, and scanning calorimetry.     

Synthesis and study of the cyclization pathways and reactivities of α-diazoimidolates

The reaction of unsymmetrical N,N-disubstituted malonamides with benzenesulfonyl azide in the presence of sodium ethoxide gives individual sodium 1,2,3-triazol-5-olates or mixtures of their isomers, from the relative amounts of which the effect of substituents in the amido groups on the cyclization pathways and reactivities of -diazoimidolates was ascertained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1521–1527, November, 1991.     

Neutron diffraction study of uranyl oxalate [UO2(C2O4)(D2O)] · 2D2O

A powdered sample of uranyl oxalate [UO₂(C₂O₄)(D₂O)] · 2D₂O (compound I) is studied using neutron diffraction. The crystals are monoclinic, space group P2₁/c, with a = 5.608(1) Å, b = 17.016(3) Å, c = 9.410(2) Å, β = 98.9369(2)°, Z = 4, R _f = 0.042, R _I = 0.054, x ² = 1.5. The main structural units of the crystals are [UO₂(C₂O₄)(D₂O)] chains. These chains, which belong to the AK⁰²M¹ (A = UO ₂ ²⁺ ) crystal-chemical group of the uranyl complexes, lie parallel to [101]. The water molecules in the crystals of I are hydrogen-bonded into zigzag chains running along [100]. Since each third oxygen atom of the chain formed of water molecules is coordinated to the uranium atom, the uranyl oxalate chains are linked into {[UO₂(C₂O₄)(D₂O)] · 2D₂O} layers that lie normal to [010]. The layers are linked into the framework through interlayer hydrogen bonds (D₂O)O-D···O (oxalate).     

Lewis acid mediated functionalization of β-lactams: mechanistic study and synthesis of C-3 unsymmetrically disubstituted azetidin-2-ones

A convenient and efficient route to novel unsymmetrically disubstituted azetidin-2-ones is described. β-Lactam carbocation equivalents of type 1 and active aromatic substrates in the presence of a Lewis acid promote a facile and stereoselective C-3 substitution to provide monosubstituted β-lactams (3,4) and symmetrically disubstituted β-lactams (5). cis-3-(4′-Methoxyphenyl)-3-phenylthioazetidin-2-ones (4) undergo further substitution with active aromatic substrates mediated by a Lewis acid to afford unsymmetrically disubstituted azetidin-2-ones (7).     

Layered xLiMO2·(1−x)Li2M′O3 electrodes for lithium batteries: a study of 0.95LiMn0.5Ni0.5O2·0.05Li2TiO3

The electrochemical properties of 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ have been investigated as part of a study of xLiMO₂·(1−x)Li₂M^′O₃ electrode systems for lithium batteries in which M=Co, Ni, Mn and M^′=Ti, Zr, Mn. The data indicate that the electrochemically inactive Li₂TiO₃ component contributes to the stabilization of LiMn_0.5Ni_0.5O₂ electrodes, which improves the coulombic efficiency of Li/xLiMn_0.5Ni_0.5O₂·(1−x)Li₂TiO₃ cells for x<1. The 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ electrodes provide a rechargeable capacity of approximately 175 mAh/g at 50 °C when cycled between 4.6 and 2.5 V; there is no indication of spinel formation during electrochemical cycling.     

Low-temperature formation of cubic β-PbF2: precursor-based synthesis and first-principles phase stability study

A precursor-based approach to the cubic β-phase of PbF(2) was developed and allowed the preparation of this high-temperature phase well below the temperature for transition from the orthorhombic α- to the cubic β-phase. The formation of β-PbF(2) from the molecular precursors Pb[Se(C(6)H(2)(CF(3))(3))](2) and Pb(C(6)H(2)(CF(3))(3))(2) is facilitated by the presence of several short PbF contacts in these molecules. The cubic form of PbF(2) was obtained as macroscopic crystals as well as nanoparticulate powder. Its formation at relatively low temperature suggested a theoretical re-investigation of the phase stabilities of the two polymorphs. The theoretical results from the Kohn-Sham density functional theory indicate that the energy content for the β-phase is slightly lower than the one for the α-phase, by 0.5-1.7 kJ mol(-1) depending on the density functional used (zero-point vibrational energy correction included).