Neutron diffraction study on protonated and hydrated layered perovskite

A layered perovskite compound with Na⁺, D₃O⁺ ions (H₃O⁺) and D₂O molecules (H₂O) in the interlayer, D_xNa_1−xLaTiO₄·yD₂O, has been prepared by an ion-exchange/intercalation reaction with dilute DCl solution, using an n=1 Ruddlesden-Popper phase, NaLaTiO₄. Its structure has been analyzed in order to clarify the interlayer structure by Rietveld method, using powder neutron diffraction data. The structure analysis revealed that the layered structure changed from the space group P4/nmm-I4/mmm after the ion-exchange/intercalation reaction, and it induced the transformation of perovskite layers from staggered to an eclipsed configuration. The D₂O molecules and D₃O⁺ ions loaded in the interlayer statistically occupied the sites around a body center position of rectangular space surrounded by eight apical O atoms of TiO₆ octahedra in upper and lower layers.     

Translational diffusion in Monte Carlo simulations of polymer melts: center of mass displacement vs. integrated velocity autocorrelation function

Translational diffusion has been simulated in monodisperse melts of four linear alkanes, C_2xH_4x+2, x=6,30,50,158, and two cyclic alkanes, C_2xH_4x, x=30,50, at 473 K. The alkanes are expressed in a coarse-grained representation using x beads on a high coordination lattice, one bead for every two carbon atoms. Short-range intramolecular interactions are controlled by an adaptation of the rotational isomeric state model for unperturbed polyethylene, and the long-range interactions are controlled by a step-wise three-shell potential energy function derived from a continuous Lennard-Jones potential energy function. Acceptance of trial moves, each of which changes the coordinates of a single bead only, is governed by the Metropolis rule. Translational diffusion coefficients, D, are estimated from the mean square displacement of the center of mass and the integral of the velocity autocorrelation function. Both approaches yield the same value for D, which demonstrates that the velocity has been defined in a reasonable manner in the Monte Carlo simulation. A method is proposed for the estimation of D when the trajectory is not quite long enough to have achieved the behavior characteristic of the limit as time approaches infinity.     

Crystal structure of β-CaNi5D0.77 by rietveld analysis of neutron powder-diffraction data

β-CaNi₅D_0.77 is orthorhombic (a = 8.6033(13) b = 5.0810(9) c = 7.8557(15)Å, Pmcm, Z = 4, D_x = 6.48 g cm^?3, V = 343.4ų, FW = 1339.8 amu. Rietveld analysis of a neutron powder-diffraction pattern shows that D atoms occupy the centers of [Ni₄Ca₂] square dipyramids (“octahedra”) linked through the Ca atoms at opposite apices and forming chains. About 80% of the deuterium atoms occupy fairly regular sites (DNi = 1.53, 1.80, 1.86, 1.86 Å; DCa = 2.42, 2.45 Å). The remaining 20% occupy very distorted sites (DNi = 1.21, 1.38, 2.07, 2.07 Å; DCa = 2.54, 2.60 Å). The average DD distance in a chain is 4.3 Å.     

The crystal structure of cubic hydrogen tungsten bronze

The structure of D_0.53WO₃ has been determined by a room temperature powder neutron diffraction study. The unit cell is body centered cubic (Im3) and contains 8 formula weights (a = 7.562 ± 0.002 Å). The average cell content was refined by a least squares method based on peak intensities. The tungsten atoms lie on the special sites of the perovskite structure and are surrounded by nearly regular octahedrons of oxygen atoms with the latter displaced from the normal perovskite positions along 〈110〉. The deuterium atoms constitute statistically distributed -OD bonds which are directed towards the nearest oxygen atom of a neighboring octahedron. The analogous hydrogen compound is best described as a nonstoichiometric oxide hydroxide WO_3?x(OH)_x based on a distorted ReO₃ structure. The crystal structure is closely related to that of In(OH)₃ and Sc(OH)₃.     

Phosphates having the NaZr2(PO4)3 structure and containing titanium (or zirconium) and elements in oxidation degree 2+ (calcium or zinc)

Complex phosphates Ca_{0.5 + x} Zn _x E_{2 ? x} (PO₄)₃ (E = Ti, Zr) having NaZr₂(PO₄)₃ (NZP) structure have been prepared and characterized by X-ray diffraction, electron probe microanalysis, IR spectroscopy, and differential thermal analysis (DTA). Their phase formation has been studied by X-ray powder diffraction and DTA. The concentration and temperature fields of existence of these NZP phases have been determined: substitution solid solutions exist in the range of compositions where 0 ≤ x ≤ 0.5. The Ca_0.7Zn_0.2Ti_1.8(PO₄)₃ crystal structure has been refined by the Rietveld method (space group \(R\bar 3\) , a = 8.3636(4) Å, c = 21.9831(8) Å, V = 1331.7(1) ų, Z = 6). The framework in the NZP structure is built of octahedra, which are populated by titanium and zinc atoms, and PO₄ tetrahedra. Calcium atoms occupy extraframework positions. Extensive solid solution formation due to the accommodation of cations(2+) in the interstices within the NZP framework (M) and in the framework-forming octahedra (M′) makes it possible to design a plurality of new M_{0.5 + x} M′ _x E_{2 ? x} (PO₄)₃ phosphates with tailored structures.     

Imidazolate bridged polynuclear rhodium(I) complexes. X-ray structure of [Rh(2-Meimidazolate)(CO)2]4

The synthesis and properties of polynuclear complexes of general formulae [M(RIm)(diolefin)_x, [M(RIm)(CO)₂]_x and [M(RIm)(CO)L]_x (M  Rh, Ir; RIm  imidazolate, 2-methylimidazolate, 2-benzylbenzimidazolate; L  PPh₃ or P(OPh)₃) are reported. The crystal structure of the novel complex [Rh(2-MeIm)-(CO)₂]₄ (2-MeIm  2-methylimidazolate) has been determined by X-ray methods. The crystals are orthorhombic, space group P2₁2₁2₁, with Z  4 in a unit cell of dimensions a 19.427(12), b 13.419(8), c 12.346(9) Å. The structure has been solved by combined Patterson and direct methods and refined by full-matrix least-squares to R  0.043 for 937 independent observed reflections. It consists of discrete tetrameric complexes in which each Rh atom is in a nearly cis square planar arrangement, bonded to two carbon atoms of carbonyl groups and to two nitrogen atoms of two 2-methylimidazolate ligands, each of which, acting as an exo-bidentate ligand, bridging two metal atoms, so that the four bridging 2-MeIm ligands and the four Rh atoms form a multiatomic ring.     

Atoms state and interatomic interactions in perovskite-like oxides: XXXII. Formation of paramagnetic clusters in the La1−0.33x Ca0.33x Fe x Al1−x O3 and La1−0.33x Sr0.33x Fe x Al1−x O3 solid solutions

Calcium- and strontium-containing lanthanum orthoferrites have been studied using magnetic dilution method. It has been shown that the iron-atom clusters with competing ferro- and antiferromagnetic exchange interactions can exist. By using Mossbauer spectroscopy, Fe(IV) atoms have been found in the La_1?0.33x Ca_0.33x Fe_xAl_1?x O₃ solid solutions and Fe(III) atoms in two different surroundings have been found in the La_1?0.33x Sr_0.33x Fe _x Al_1?x O₃ solid solutions. The compositions of paramagnetic clusters stable at the infinite dilution have been proposed basing of the magnetic susceptibility and Mossbauer spectroscopy data.     

Structural and magnetic properties of RMn2−xFexD6 compounds (R=Y, Er; x≤0.2) synthesized under high deuterium pressure

RMn_2−xFe_xD₆ compounds were obtained by applying a deuterium pressure of several kbar to RMn_2−xFe_x compounds for x≤0.2 and R=Y, Er. These compounds are isostructural to RMn₂D₆ compounds and crystallize in a K₂PtCl₆ type structure with a random substitution of R and half the Mn atoms in the same 8c site whereas the other Mn atoms are located on the 4a site and surrounded by six D atoms (24e site). According to neutron powder diffraction analysis the Fe atoms are preferentially substituted on the 4a site. YMn_2−xFe_xD₆ compounds are paramagnetic and their molar susceptibility follows a modified Curie-Weiss law. ErMn_2−xFe_xD₆ compounds display a ferromagnetic behavior at 2 K, but their saturation magnetization (M_S∼4.0 μ_B/f.u.) is half that of their parent compounds (M_S∼8.0 μ_B/f.u.). The neutron diffraction patterns of ErMn_1.8Fe_0.2D₆ display below 13 K both ferromagnetic and antiferromagnetic short range order, which can be related to a disordered distribution of Er moments. The paramagnetic temperatures of ErMn_2−xFe_xD₆ compounds are negative and decrease versus the Fe content whereas they are positive and increase for their parent compounds.     

Metals in Biochemistry : P.M. Harrision and R.J. Hoare. Publ. Chapman & Hall,London and New York 1980, 78 pp + index. Price £2.45

The complex H₂Os₃(μ₃-NCH₃)(CO)₁₂ in decalin at 198°C in 35% yield. Crystal data for the former obtained at ?158°C are: orthorhombic, space group Pmcn, a 14.113(2), b 6.605(1), c 17.683(4) », Z = 4, D_c 3.44 g cm^?3. The hydrogen atoms are related by symmetry. The position of the unique hydrogen atom has been refined. It is observed asymmetrically bridging (closer to the unique Os atom) the longer edge of the isosceles triosmium triangle. The hydrogen atoms are out of the trimetal plane away from the triply-bridging nitrogen atom.Crystal data for the tetraosmium complex at 25°C are: monoclinic, space group C2/c a 30.818(9), b 8.463(2), c 16.621(2), », β 108.90(2)°, Z = 8, D_c 3.75 g cm^?3. The four osmium atoms form a distorted tetrahedral framework capped by the nitrogen atom of the methylnitrene group on the face containing the three longer OsOs separations.     

Lanthanum Gallium Tin Antimonides LaGaxSnySb2

A series of quaternary lanthanum gallium tin antimonides LaGa_xSn_ySb₂ was elaborated to trace the structural evolution between the known end members LaGaSb₂ (SmGaSb₂-type) and LaSn_ySb₂ (LaSn_0.75Sb₂-type). Five members of this series were characterized by single-crystal X-ray diffraction. For low Sn content, the Sn atoms disorder with Ga atoms in zigzag chains to form solid solutions LaGa_1-ySn_ySb₂ (0≤y≤0.2) adopting the SmGaSb₂-type structure, as exemplified by LaGa_0.92(3)Sn_0.08Sb₂ and LaGa_0.80(3)Sn_0.20Sb₂ (orthorhombic, space group D⁵₂−C222₁,Z=4). For higher Sn and lower Ga content, there is a segregation in which the Sn atoms appear in chains of closely spaced partially occupied sites as in the parent LaSn_0.75Sb₂-type structure whereas the Ga atoms remain in zigzag chains as in the parent SmGaSb₂-type structure. This feature is observed in the structures of LaGa_0.68(4)Sn_0.31(3)Sb₂, LaGa_0.62(3)Sn_0.32(3)Sb₂, and LaGa_0.43(3)Sn_0.39(3)Sb₂ (orthorhombic, space group D¹⁷_2h−Cmcm,Z=4). The last example illustrates that the combined Ga/Sn content can be substoichiometric (x+y<1). These compounds have a layered nature, with the chains of Ga or Sn atoms residing between ²_∞[LaSb₂] slabs.     

Compositions and structures of nanoparticles of trigonal symmetry <Emphasis Type="Italic">D</Emphasis><Subscript>3<Emphasis Type="Italic">d</Emphasis></Subscript>: Nanotubes

A method has been developed for the determination of the structure and number of atoms in the shells of nanoparticles as a function of the arrangement of atoms at the symmetry elements of a symmetry group. The formulas for calculation of the number of particles of symmetry D _3d have been reported. It has been shown that the number of atoms in trigonal shells is determined by three structurally invariant numbers and the quantum number of the group order n. All possible nanostructures of symmetry D _3d have been classified: C_{θ + 6z} , z = 0, 1, 2, ..., where the basic shells are C_θ = C₆, C₈, and C₁₄. A sum rule has been obtained for the coordination numbers of the shell sites located on symmetry axes. Trigonal nanoparticles are parent ones for obtaining (3,0), (6,0), and (9,0) nanotubes of trigonal type. The general formulas of these nanotubes with icosahedral, dodecahedral, and cubic caps are N_{8 + 12p} , N_{20 + 24p} , and N_{60 + 36p} (p = 1, 2, ...), respectively. The graphical constructions of all classes of trigonal nanoparticles and nanotubes are reported.     

Die Struktur der Komplexnitride NbCrN und Ta1−x Cr1+x N

The crystal structure of the isotypic compounds NbCrN and Ta_1?x Cr_1+x N has been determined from X-ray powder patterns. The tetragonal unit cell contains 12 atoms and belongs to the space group P4bm. The lattice parameters are for NbCrN:a=4.283 Å,c=7.360 Å, for Ta_0.8Cr_1.2Na=4.249 Å,c=7.334 Å. The structure is characterized by relatively close packed double layers of Nb(Ta)-atoms and Cr-atoms parallel to the base plane. The nitrogen atoms are within the octahedral interstitial sites of the niobium(tantalum) double layer.     

Preparation,characterization and crystal structure of N,N-dimethylanilinium β-octamolybdate dihydrate

N,N-dimethylanilinium β-ocatmolybdate dihydrate has been synthesized in acidic aqueous solution. The compound has been identified by using TG, DTG, IR and ¹H NMR techniques. It crystallizes in the triclinic system, space group PĪ, Z = 1, a = 11.755(3) Å, b = 11.836(5) Å, c = 10.498(2) Å, α = 105.29(2)°, β = 81.56(3)°, γ = 115.24(3)°, V = d1273.4(8) Å, D_o = 2.23(1) Mg m⁻³, D_x = 2.23 Mg m⁻³, R = 0.029 and R₂ = 0.032 for 5259 observed reflexions. Two crystallographically independent [C₈H₁₂N]⁺ cations, one water molecule and one centrosymmetric β-octamolybdate polyanion are present in the asymmetric unit. Hydrogen bonds of types NH ···O and OH···O seem to stabilize the structure.     

Theoretical identification of the lowest-energy structure of (SiC)12 heterocluster: Segregation of C and Si in planar and cage structures

The structures and relative stabilities of various plane and cage isomers of (SiC)₁₂ cluster have been systematically computed using density functional theory at the level of BLYP. A number of starting configurations were generated from the low-energy isomers of C₂₄ cluster via replacing 12 C atoms by Si atoms, which are D_6h planar structure, and the D_6d, D_2h, O_h, and D_4h symmetrical fullerene cages. The heterofullerene cage obeying six isolated squares rules are not the most preferred structural motif for (SiC)₁₂ cluster. The structural candidates with fully alternating Si–C arrangement are energetically unfavorable. Instead, the (SiC)₁₂ cluster tend to adopt plane, bowl, saddle, and highly distorted cage structures. In all cases, segregation of C atoms is a common feature.     

The crystal structures of a series of cubic hydrogen insertion compounds of the mixed molybdenum tungsten oxides

The structures of three hydrogen insertion compounds, D_0.56Mo_0.25W_0.75O₃, D_0.80Mo_0.5W_0.5O₃, and D_0.81Mo_0.69W_0.31O₃, were determined from powder neutron diffraction studies. All three compounds were body centered cubic (space group Im3) with the unit cell containing eight formula weights. The lattice parameter a = 7.5558(6), 7.587(1), and 7.5743(5) Å, respectively. A least-squares method based on peak intensities was used to determine the structures. The metal atoms lie on the special perovskite sites and are surrounded by nearly regular octahedra of oxygen atoms with the latter displaced from the normal perovskite positions along 〈110〉. The deuterium atoms are distributed over 48 sites in the unit cell and form —OD bonds directed toward the nearest oxygen atom in a neighboring octahedron. These compounds have the same structure as the cubic hydrogen tungsten bronze H_0.53WO₃.     

Investigation of structural and hydrogen absorption properties in the LaNi5−xPtx-H2 system

The substitution of nickel by platinum in the binary LaNi₅ compound (CaCu₅ structure type, a=5.019(1) Å, c=3.981(1) Å, space group P6/mmm) and its effect on the hydrogenation properties was studied. The phase LaNi_5−xPt_x has a homogeneity domain ranging from x=0 to 5. For x<3, platinum substitutes almost exclusively on site 3g and also replaces nickel on site 2c for x>3. Contrary to what is observed in other systems, the hydrogen absorption plateau pressure was found to increase as a function of the cell volume. Powder neutron diffraction experiments were conducted for two deuterated compounds with x=0.25 and 0.75. Deuterium partial ordering occurs in the case of x=0.25 leading to a symmetry decrease to the space group P6mm (LaNi_4.75Pt_0.25D_5.23, a=4.225(1) Å, c=5.357(1) Å, Z=1, R_Bragg=3.3%). For x=0.75, an orthorhombic superstructure based on the CaCu₅-type lattice was found (LaNi_4.25Pt_0.75D_2.61, a_orth=√3a_hex=9.089(1) Å, b_orth=b_hex=5.272(1) Å, c_orth=2c_hex=8.145(1) Å, Z=4, SG Ibam, R_Bragg=6.1%).     

Interaction of water-DMSO mixtures with cellulose

The character of the interaction of cellulose with water-dimethyl sulfoxide mixtures is investigated. It is shown that, in the concentration range 0 < x _D < 0.28, cellulose predominantly sorbs water; in this case, in the presence of small amounts of DMSO (x _D ～ 0.1), the sorption is higher than that for pure water. It is established that the formation of hydrogen bonds between hydroxyl groups of cellulose and oxygen atoms in DMSO molecules is most probable at x _D > 0.6, where large clusters dominate over hydrophobic dimers.     

Structure de benzoates de fluoroalkyles

The crystal and molecular structure of 2,2,3,3-tetrafluoropropyl-parachlorobenzoate (C₁₀H₇ClF₄O₂) has been determined by X-ray diffraction. The crystals are monoclinic, P2₁, a = 4.826(1), b = 9.036(2), c = 12.442(4)Å, β = 94.64(2)°, V = 540.8 ų, Z = 2, D_x = 1.66 Mg m^?3. Starting from the ¹³C data of this compound, the identification of five other fluoroalkylbenzoates has been achieved by N.M.R. spectroscopy.     

Elastic and inelastic neutron studies of hydrogen molybdenum bronzes

Hydrogen molybdenum bronzes H_xMoO₃ (～0.3 < x < 2.0) have been investigated with elastic and inelastic neutron scattering. Neutron diffraction studies of orthorhombic D_0.36MoO₃ show that deuterium is incorporated as -OD without any major structural change to the MoO₃ layer lattice. The inelastic neutron scattering spectra of H_xMoO₃ phases confirm that, for H_0.34MoO₃, H is present as -OH, but, for the monoclinic phases H_0.93MoO₃, H_1.68MoO₃ and H_2.0MoO₃, only peaks associated with -OH₂ groups are found.     

Electronic properties and crystal structure of aqua (mepirizole-oxalato)copper(II)monohydrate: [Cu(C11H14N4O2)C2O4·H2O]H2O

A Cu(ll) complex with mepirizole: 4-methoxy-2-(5-methoxy-3-methyl-pyrazoll-yl)-6-methylpyrimidine (L) and oxalate as ligands with the formula [CuL(C₂O₄)(H₂O)]·H₂O has been synthesized. The crystal structure has been determined by X-ray diffraction analysis: monoclinic, space group P2₁/n, Z = 4, a = 7.707(1), b = 14.951(3), c = 14.986(2) Å,β = 92.40(2)°, V = 1725.2(8) ų, D_m = 1.61(1) g cm⁻³, D_c = 1.62 g cm⁻³, R = 0.032 and R_w = 0.035 for 2016 observed reflections. The CuN₂O₂O′chromophore can be described as square pyramidal strongly distorted towards trigonal bipyramidal. The basal coordination positions are occupied by the two oxygen atoms of the bidentate oxalate group, the coordinated water molecule and one nitrogen atom of the bidentate mepirizole group; the other coordinated nitrogen atom occupies the apical position. Magnetic moment, IR, electronic reflectance and ESR spectra are interpreted in accordance with the proposed stereochemistry.