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Heteropolynuclear metal organic frameworks (MOFs) of the general formula [Ln2Ni3(oda)6(H2O)6]·xH2O (oda = oxydiacetate, Ln = +3 rare earth ion) were synthesized and characterized. Most of them bear a honeycomb structure with 1D channels containing 11 to 14 crystallization water molecules per formula unit. The size of the channels and the number of crystallization water molecules they contain decrease as the Ln ionic radii become smaller along the series from La to Tm. In addition, the water content changes reversibly with temperature and relative humidity conditions. Accordingly, the as-synthesized [Tm2Ni3(oda)6(H2O)6]·11H2O picks up water when exposed to a 100% relative humidity atmosphere to become [Tm2Ni3(oda)6(H2O)6]·14H2O. Computational calculations show the formation of a hydrogen bond network in which layers of water molecules are arranged and associated primarily to the polar groups of the framework walls, anticipating good proton conduction along the [001] channels. Furthermore, higher confinement of water molecules in the smaller channels could favor the water molecules' mobility. Indeed, the proton conductivity of [Tm2Ni3(oda)6(H2O)6]·14H2O is 2.43 × 10−3 S cm−1 at 70 °C, similar to that of standard conductive MOF-based materials reported. A vehicular carrier mechanism by means of H3O+ species diffusing along the 1D channels of the porous structure seems to be operative, with a high activation energy value of 1.46 eV.

The structure of catena-[tris­(μ4-benzene-1,4-di­carboxyl­ato)-tetra­kis­(μ1– di­methyl­formamide-κ1 O)-trinickel(II)], C36H40N4Ni3O16, has been determined in the monoclinic P21/n space group. The compound has a two-dimensional coordination network structure and it is of inter­est with respect to lithium-ion battery applications. Hirshfeld surface analysis was performed to characterize inter­planar inter­actions. The structure exhibits disorder of coordinated solvent mol­ecules., The crystal structure of the title compound, [Ni3(C8H4O4)3(C3H7NO)4], is a two-dimensional coordination network formed by trinuclear linear Ni3(tp)3(DMF)4 units (tp = terephthalate = benzene-1,4-di­carboxyl­ate and DMF = di­methyl­formamide) displaying a characteristic coordination mode of acetate groups in polynuclear metal–organic compounds. Individual trinuclear units are connected through tp anions in a triangular network that forms layers. One of the DMF ligands points outwards and provides inter­actions with equivalent planes above and below, leaving the second ligand in a structural void much larger than the DMF mol­ecule, which shows positional disorder. Parallel planes are connected mainly through weak C—H⋯O, H⋯H and H⋯C inter­actions between DMF mol­ecules, as shown by Hirshfeld surface analysis.

The structure of the title compound, C32H51NO6, was determined from 62-year-old crystals at room temperature and refined with 100 K data in a monoclinic (C2) space group. This compound with a triterpenoid structure, now confirmed by this study, played an important role in the determination of the structure of lanosterol. The molecules pack in linear O—H...O hydrogen-bonded chains along the short axis (b), while parallel chains display weak van der Waals interactions that explain the needle-shaped crystal morphology. The structure exhibits disorder of the flexible methylheptane chain at one end of the main molecule with a small void around it. Crystals of the compounds were resistant to data collection for decades with the available cameras and Mo Kα radiation single-crystal diffractometer in our laboratory until a new instrument with Cu Kα radiation operating at 100 K allowed the structure to be solved and refined.

A modified synthesis procedure allowed lapachol acetate (acetic acid 3-(3-methyl-but-2-en­yl)-1,4-dioxo-1,4-di­hydro- naphthalen-2-yl ester) to be obtained in high yield and its crystal structure is reported for the first time 80 years after its first synthesis. The lapachol acetate mol­ecular conformation is very similar to that of reported lapachol mol­ecules and other derivatives. The monoclinic P21/n crystal structure packs through weak inter­molecular π–π and C—H⋯O inter­actions as described by Hirshfeld surface analysis., Lapachol acetate [systematic name: 3-(3-methyl­but-2-en­yl)-1,4-dioxonaph­thalen-2-yl acetate], C17H16O4, was prepared using a modified high-yield procedure and its crystal structure is reported for the first time 80 years after its first synthesis. The full spectroscopic characterization of the mol­ecule is reported. The mol­ecular conformation shows little difference with other lapachol derivatives and lapachol itself. The packing is directed by inter­molecular π–π and C—H⋯O inter­actions, as described by Hirshfeld surface analysis. The former inter­actions make the largest contributions to the total packing energy in a ratio of 2:1 with respect to the latter.

New bond valence R0 parameters were derived for alkali– and alkaline-earth–oxygen pairs encountered in metal−organic compounds. A total of 7693 metal−oxygen bond lengths were extracted from structures deposited in the Cambridge Structural Database (CSD) and containing at least one carboxylate ligand bound to the metal. One hundred structures were individually analyzed for each metal. R0 values were computed using two different approaches: geometric mean and graphical fitting. In both cases, the bond valence parameter b was fixed at 0.37 A. R0 values obtained using a geometric mean approach were 1.744 (Na–O), 2.094 (K–O), 2.228 (Rb–O), 2.412 (Cs–O), 1.661 (Mg–O), 1.933 (Ca–O), 2.090 (Sr–O), and 2.265 A (Ba–O). These parameters yielded more accurate metal bond valence sums (BVS) and lower root-mean square deviations (RMSD) than those computed using R0 values currently available in the literature,1 which had been derived from the structures of inorganic oxides. The most significant improvement was observed for sodium (this work mean BVS = 1.01 v.u., RMSD = 0.116 v.u.; literature mean BVS = 1.18 v.u., RMSD = 0.226 v.u.; v.u.: valence units) and magnesium (this work mean BVS = 2.00 v.u., RMSD = 0.038 v.u.; literature mean BVS = 2.18 v.u., RMSD = 0.100 v.u.). More accurate bond valence sums and lower variances were also observed when the new set of R0 values was applied to metal–organic compounds featuring oxygenated ligands such as ethers, ketones, aldehydes, alcohols, and esthers. These parameters should be applicable to the structural and crystal-chemical analysis of metal−organic compounds ranging from coordination complexes to organic−inorganic extended hybrids.

An experimental investigation of the structure and crystal-chemistry of the triple perovskite BaSr2MgTa2O9 is reported. Polycrystalline BaSr2MgTa2O9 was synthesized via solid-state reaction and its structure quantitatively probed at 10 and 300 K using neutron diffraction. Monoclinic (A2/m, a0 b ¯ – b–) and trigonal structural models (P 3 ¯ c1, a–a–a–) were fit to diffraction data. The former was found to correctly reproduce experimental intensities, while the latter failed to do so. This difference is attributed to the ability of the monoclinic model to accurately reflect octahedral tilting. BaSr2MgTa2O9 features corner-sharing MgO6 and TaO6 octahedra with barium and strontium cations occupying cubooctahedral holes. Barium and strontium are disordered over the A site, whereas B site cations magnesium and tantalum are ordered. Chemical substitution of strontium for barium in Ba3MgTa2O9 induces tilting of MgO6 and TaO6 octahedra in two directions and geometric distortions of MgO6 octahedra.

The crystal structure of divainillin (systematic name: 6,6′-dihydroxy-5,5′-dimethoxy-[1,1′-biphenyl]-3,3′-dicarbaldehyde), C16H14O6, was determined from laboratory powder X-ray diffraction data using the software EXPO2013 (direct methods) and WinPSSP (direct-space approach). Divanillin molecules crystallize in the orthorhombic space group Pba2 (No. 32), with two molecules per unit cell (Z′ = 1 \over 2). Each divanillin molecule, with twofold symmetry, is linked through strong alcohol–aldehyde hydrogen bonds to four equivalent molecules, defining a three-dimensional hydrogen-bonding network, with rings made up of six divanillin units (a diamond-like arrangement). Each molecule is also connected through π–π interactions to a translation-equivalent molecule along c. Four consecutive molecules stacked along [001] belong to four different three-dimensional hydrogen-bonding networks defining a quadruple array of interpenetrating networks. This complex hydrogen-bonding array is proposed as an explanation for the aging process experienced by divanillin powders.

Considering the importance of quinolones due to their broad spectrum of biological activities, the crystal structure of the title compound, C22H21NO3·0.5C7H16, has been determined. Two enantiomers of the benzazepinoquinoline molecule and one molecule of heptane form the asymmetric unit of this centrosymmetric triclinic (P\overline{1}) crystal. All the molecules in the crystal present disorder. Substitutional disorder is observed for the benzazepine molecules, where a minority conformer of the R enantiomer replaces the main conformer of the S enantiomer and vice versa. Positional disorder is found for the heptane solvent molecule, which occupies a void left by the independent enantiomers of both conformers.

The preparation of oxyfluoroborate glasses and glass–ceramics doped with Yb3+ and Er3+ with improved luminescent properties is reported. Glasses with compositions (100 − x − y) (MO·2B2O3) + xPbF2 + y(YbF3:ErF3) (% in mol), where M is Sr, Ba, Ca, x = 10–40% and y = 0, 1 or 5% were prepared by the melt/quenching technique. Glass crystallization was studied using thermal analysis and X-ray diffraction techniques. Optical absorption and infrared up-conversion were studied on both glasses and glass–ceramics. The incorporation of a fluoride compound into the borate glass resulted to depend on the ionic radius of the glass modifier: as it increases, glasses become more stable against crystallization. On the other hand, alkali–fluoride compounds such as BaF2 and SrF2 can be crystallized from these systems by selecting an appropriate proportion between their components. Furthermore, the up-conversion response can be tuned by changing the glass modifiers (Sr, Ba and Ca) of the borate matrix, which also influence the type of fluoride crystallized compound. The strontium glass–ceramics have the highest luminescence response due to the crystallization of SrF2 compound in the system SrO–B2O3–PbF2. Meanwhile, the lowest luminescence signal was obtained for samples in the system BaO–B2O3–PbF2 where the Pb1.33Ba2.66B11FO20 phase crystallizes. With this strategy, new materials with improved luminescence properties that can be used as up converters, were obtained.

Using the flexible ligand oxydiacetic acid (H2oda), ten new heteropolynuclear compounds with general formula [Ln2Zn3(oda)6]·xH2O (Ln = lanthanide ion, oda = oxydiacetate) were synthesized and structurally characterized. They were prepared by the direct reaction of oda in aqueous solution with stoichiometric amounts of Zn and Ln salts, followed by slow organic solvent diffusion. Two different structures were obtained: the larger lanthanides Pr, Nd, Eu and Tb gave compounds belonging to the hexagonal system, space group P6/mcc; whereas, the smaller ones, Ho, Er, Yb and Y formed cubic systems, space group Fdc. In the case of Dy, the two polymorphs were obtained by slight variations in the synthetic conditions. The phase change observed is discussed in comparison with previously reported [Ln2M3(oda)6]·xH2O compounds (M = bivalent metal ion). Luminescence studies were also carried out. Compounds containing Eu and Tb showed the most intense luminescence, also bearing relatively long lifetimes for the excited state deactivation. The luminescence profiles of both Dy systems are independent of the hexagonal or cubic arrangements, due to the similar environment of the Ln having the same point symmetry.

The absolute configuration of the title compound, determined as 4S,5R,6S on the basis of the synthetic pathway, was confirmed by single-crystal X-ray diffraction. The mol­ecule is formed by a substituted six-membered cyclo­hexene ring adopting an envelope conformation and substituted by carbonyl, methyl and hydroxyl groups. The supra­molecular structure is mainly built by a combination of O—H⋯O and weaker C—H⋯O hydrogen bonds., The mol­ecule of the title keto carbasugar, C7H10O4, is formed by a cyclo­hexene skeleton with an envelope conformation, substituted by carbonyl, methyl and hydroxyl groups. The crystal structure is controlled mainly by a combination of strong O—H⋯O and weak C—H⋯O hydrogen bonds, forming nearly perpendicular chains running parallel to the [110] and [-110] directions. This perpendicularity is caused by a tetra­gonal pseudosymmetry influenced by the similarity between the a and b axes, the value of 90.9770 (10)° of the β angle and the action of a 21 screw axis, which transform each chain into its corresponding nearly orthogonal one.

The absolute configuration,i.e.(3aR,3′aR,7aS,7′aS), of the title compound, C18H26O4, synthesizedviaa palladium-catalyzed homocoupling reaction, was determined on the basis of the synthetic pathway and was confirmed by X-ray diffraction. The homocoupled molecule is formed by two chemically identical moieties built up from two five- and six-membered fused rings. The supramolecular assembly is controlled mainly by C—H...O interactions that lead to the formation of hydrogen-bonded chains of molecules along the [001] direction, while weak dipolar interactions and van der Waals forces hold the chains together in the crystal structure.

La4BaCu5O13 + δ (LBCu) and La6.4Sr1.6Cu8O20 ± δ (LSCu) oxygen deficient perovskites, synthesized by a Pechini-type gel combustion method, have been investigated as potential cathode materials for IT-SOFC applications. The thermal stability and chemical compatibility with SOFC/PCFC electrolyte materials are examined using X-ray diffraction technique. For both compounds, no structural change is detected in air until 900 °C. The evolution of cell parameters with temperature shows thermal expansion coefficients (TEC) of 17.3 × 10− 6 K− 1 and 12.1 × 10− 6 K− 1 for LBCu and LSCu, respectively. For LBCu, the formation of oxygen vacancies is evidenced between 700 and 900 °C in air. Chemical reactivity tests with several SOFC electrolyte materials reveal a high reactivity of both cuprates with YSZ, GDC and, to a lesser extent, with LSGM. On the other hand, and contrary to what occurs for LSCu, LBCu presents an excellent chemical compatibility with doped barium cerate and zirconate, opening further perspectives for this material as possible SOFC or PCFC cathode. LBCu material presents a quite high electrical conductivity with metallic-type behavior.

La 4 BaCu 5−x Co x O 13+δ system was successfully synthesized by a modified Pechini route in air. A structural phase transition is observed along the series, from tetragonal ordered structure for 0 ≤ x ≤ 2 to a rhombohedral disordered perovskite for x = 5. A TEC value of 17.3 × 10 −6 K −1 , was found by High-Temperature X-ray Diffraction (HT-XRD) in air for La 4 BaCu 3 Co 2 O 13+δ . The conductivity of La 4 BaCu 3 Co 2 O 13+δ increases with temperature reaching a maximum of 778 S cm −1 at 405 °C in air followed by a decrease with further increase in temperature with values of 600–664 S cm −1 . The cathode polarization resistance of La 4 BaCu 3 Co 2 O 13+δ evaluated in air at 750 °C is 0.34 Ω cm 2 with an activation energy of 1.65 eV. These results demonstrate the possible use of La 4 BaCu 5−x Co x O 13+δ materials as cathode for Intermediate-Temperature Solid Oxide Fuel Cell (IT-SOFC). Fil: Duran, Silvia. Universidad Industrial Santander; Colombia. Universidad de la República; Uruguay Fil: Téllez Bernal, Jhoan Francisco. Universidad Industrial Santander; Colombia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Sandoval, Mónica V.. Universidad Industrial Santander; Colombia Fil: Macias, Mario A.. Universidad de la República; Uruguay Fil: Capoen, Edouard. Universidad Industrial Santander; Colombia Fil: Pirovano, Caroline. Universidad de Los Andes, Colombia; Colombia. Universidad de la República; Uruguay Fil: Roussel, Pascal. Universidad Industrial Santander; Colombia Fil: Niemczyk, Anna. Universite Lille; Francia. Universidad de la República; Uruguay Fil: Barrera Castillo, Mónica. Universite Lille; Francia Fil: Mogni, Liliana Verónica. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Suescun, Leopoldo. Universidad de la República; Uruguay Fil: Gauthier, Gilles H.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

The crystal structure of enanti­opure (3aS,4S,5R,7aR)-2,2,7-trimethyl-3a,4,5,7a- tetra­hydro-1,3-benzodioxole-4,5-diol shows that the absolute configuration determined from the synthesis pathway agrees with that determined by X-ray analysis., The absolute configuration of the title compound, C10H16O4, determined as 3aS,4S,5R,7aR on the basis of the synthetic pathway, was confirmed by X-ray diffraction. The mol­ecule contains a five- and a six-membered ring that adopt twisted and envelope conformations, respectively. The dihedral angle between the mean planes of the rings is 76.80 (11)° as a result of their cis-fusion. In the crystal, mol­ecules are linked by two pairs of O—H⋯O hydrogen bonds, forming chains along [010]. These chains are further connected by weaker C—H⋯O inter­actions along [100], creating (001) sheets that inter­act only by weak van der Waals forces.

Nanocrystalline La0.6Sr0.4Fe0.8Cu0.2O3-δ (LSFCu) material was synthetized by combustion method using EDTA as fuel/chelating agent and NH4NO3 as combustion promoter. Structural characterization using thermodiffraction data allowed to determine a reversible phase transition at 425 °C from a low temperature R-3c phase to a high temperature Pm-3m phase and to calculate the thermal expansion coefficient (TEC) of both phases. Important characteristics for cathode application as electronic conductivity and chemical compatibility with Ce0.9Gd0.1O2-δ (CGO) electrolyte were evaluated. LSFCu presented a p-type conductor behavior with maximum conductivity of 135 S cm-1 at 275 °C and showed a good stability with CGO electrolyte at high temperatures. This work confirmed that as prepared LSFCu has excellent microstructural characteristics and an electrical conductivity between 100 and 60 S cm-1 in the 500-700 °C range which is sufficiently high to work as intermediate temperature Solid Oxide Fuel Cells (IT-SOFCs) cathode. However a change in the thermal expansion coefficient consistent with a small oxygen loss process may affect the electrode-electrolyte interface during fabrication and operation of a SOFC. Fil: Vázquez, Santiago. Universidad de la República; Uruguay Fil: Davyt, Sebastián. Universidad de la República; Uruguay Fil: Basbus, Juan Felipe. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Soldati, Analía Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Amaya, Alejandro. Universidad de la República; Uruguay Fil: Serquis, Adriana Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Faccio, Ricardo. Universidad de la República; Uruguay Fil: Suescun, Leopoldo. Universidad de la República; Uruguay

The design of white-light emitting materials for solid-state lighting technology is governed by the combination of independent red, green and blue emitting centers. Many mixed-lanthanide single phase white-light source materials have been produced so far by a careful trial and error combination of lanthanide ions during the synthetic procedure. In this work we propose a simple and efficient method for the direct preparation of the desired material with the optimal combination of metal ions, avoiding the trial and error multiple synthetic approach. In the proposed strategy, the emission profiles of the isostructural complexes of each lanthanide ion for a chosen excitation wavelength are compared relative to their ion density and the necessary final composition of the material is calculated in order to obtain the white-light CIE coordinates. Using this method, we prepared a white-light emitting material which is a metal-organic framework built from oxydiacetate ligand, lanthanide ions (Eu, Tb and Dy emitting red, green and blue respectively) and zinc (a closed shell metal ion that has proven to be ideal for optical applications). The compound [Dy1.60Eu0.38Tb0.02Zn3(oda)6(H2O)6]·12H2O was prepared and fully characterized by single crystal x-ray diffraction, its optical properties were also measured. The proposed rational mixing of lanthanide ions could be useful for the preparation of white-light source materials in analogous systems, provided the single-lanthanide compounds are isostructural along the series and no optical interaction is operative among ions.

La 4 BaCu 5-x Mn x O 13+δ materials have been synthesized by the sol-gel method in air and studied as possible electrode materials for symmetrical Solid Oxide Fuel Cells (S-SOFC). Within the series, La 4 BaMn 5 O 13+δ (LBMn) exhibits an excellent stability in reducing atmosphere and remarkable redox stability, although a structure transition from rhombohedral to cubic perovskite structure is found beyond 500 °C in air or wet diluted hydrogen. The thermal expansion coefficients (TEC), deduced from HT-XRD study during redox cycling, make the manganite compatible with classical SOFC electrolytes at low temperature; however, relatively high values of 15.8(5) and 18.1(2) K −1 are found in cathode and anode conditions for T > 500 °C. With high electrical conductivities of 178 and 33.3 S cm −1 , in air and hydrogen at 800 °C, we demonstrate that the La 0.8 Ba 0.2 MnO 3 ± δ manganite fulfils all the preliminary requirements of an electrode material for symmetrical SOFC.

The crystal structure of 1,3-bis­(1H-benzotriazol-1-ylmeth­yl)benzene shows an inter­esting three-dimensional assembly influenced by its non-planar mol­ecular conformation., The mol­ecular structure of the title compound, C20H16N6, contains two benzotriazole units bonded to a benzene nucleus in a meta configuration, forming dihedral angles of 88.74 (11) and 85.83 (10)° with the central aromatic ring and 57.08 (9)° with each other. The three-dimensional structure is controlled mainly by weak C—H⋯N and C—H⋯π inter­actions. The mol­ecules are connected in inversion-related pairs, forming the slabs of infinite chains that run along the [-110] and [110] directions.

Tetrahydro-1-benzazepines have been described as potential antiparasitic drugs for the treatment of chagas disease and leishmaniasis, two of the most important so-called `forgotten tropical diseases' affecting South and Central America, caused byTrypanosoma cruziandLeishmania chagasiparasites, respectively. Continuing our extensive work describing the structural characteristics of some related compounds with interesting biological properties, the crystallographic features of three epoxy-1-benzazepines, namely (2SR,4RS)-6,8-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (1), (2SR,4RS)-6,9-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (2), and (2SR,4RS)-8,9-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (3), all C22H21NO, and two 1-benzazepin-4-ols, namely 7-fluoro-cis-2-[(E)-styryl]-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C18H18FNO, (4), and 7-fluoro-cis-2-[(E)-pent-1-enyl]-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C15H20FNO, (5), are described. Some peculiarities in the crystallization behaviour were found, involving significant variations in the crystalline structures as a result of modest changes in the peripheral substituents in (1)–(3) and the occurrence of discrete disorder due to the molecular overlay of enantiomers with more than one conformation in (5). In particular, an interesting phase change on cooling was observed for compound (5), accompanied by an approximate fourfold increase of the unit-cell volume and a change of theZ′ value from 1 to 4. This transition is a consequence of the partial ordering of the pentenyl chains in half of the molecules breaking half of the \overline{3} symmetry axes observed in the room-temperature structure of (5). The structural assembly in all the title compounds is characterized by not only (N,O)—H...(O,N) hydrogen bonds, but also by unconventional C—H...O contacts, resulting in a wide diversity of packing.

The structure of the metal–organic framework (MOF) compound [{Ca(H2O)6}{CaGd(oxydiacetate)3}2]·4H2O was determined by single-crystal X-ray diffraction and refined using conventional single-crystal X-ray diffraction data. In addition, the structure was refined using powder diffraction data collected from two sources, a conventional X-ray diffractometer in Bragg–Brentano geometry and a 12-detector high resolution synchrotron-based diffractometer in transmission geometry. Data from the latter were processed in three different ways to account for crystalline decay or radiation damage. One dataset was obtained by averaging the multiple detector patterns, another dataset was obtained by cutting the non-overlapping portions of each detector to consider only the first few minutes of data collection and a dose-corrected dataset was obtained by fitting the independent peaks in every dataset and extrapolating the intensity and peak position to the initial time of data collection or to zero-absorbed dose. The compared structural models obtained show that special processing of powder diffraction data produced a much accurate model, close to the single-crystal-based model for this particular compound with heavy atoms in high symmetry positions that do not contribute to a significant number of diffraction intensities.

B-site disordered RFe{sub 0.5}V{sub 0.5}O{sub 3} compounds, with R=La, Nd, Eu and Y, have been prepared by solid-state reaction technique and their structures and magnetic properties have been investigated through X-ray powder diffraction, time-of-flight neutron powder diffraction and magnetization measurements at temperatures ranging from 5 to 700 K. The four compounds can be described as distorted perovskites with space group symmetry Pbnm and a{sup +}b{sup -}b{sup -} tilt system. The studied compounds also show antiferromagnetic ordering with Neel temperatures of 299, 304, 304, and 335 K respectively. The magnetic structures of R=La, Nd and Y compounds were determined from the neutron powder diffraction as Gz with observed magnetic moments of 2.55, 2.54 and 2.69 {mu}{sub B} at 30, 40 and 40 K, respectively.

This work focuses on the polynuclear complexes formed by a lanthanide ion (Ln), a bivalent cation (M) and oxydiacetate (oda) as bridging ligand, with general formula [Ln2M3(oda)6(H 2O)6] · xH2O. The complexes can adopt more than one polymorphic structure, being the hexagonal (P6/mcc) and cubic (Fd3c) the most noticeable, as determined by x-ray powder diffraction. The influence of Ln and M on the solid-state structure is discussed. In addition, potentiometric studies are performed to support the existence of polynuclear species in solution. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structural and magnetic studies are presented for the perovskite type Sr1−xLaxCo0.5Fe0.5O3−δ (0⩽x⩽0.5) materials annealed under moderately high-oxygen pressures of ∼200 atm. A detailed analysis of the room temperature neutron time-of-flight diffraction data reveals that the crystal structure of the sample SrCo0.5Fe0.5O2.89(1), previously described as vacancy-disordered cubic, is similar to the formerly reported, oxygen-vacancy ordered Sr8Fe8O23 compound, i.e. Sr8Co4Fe4O23 is tetragonal with the I4/mmm symmetry. With an increase of the La content the studied materials become nearly oxygen stoichiometric and a lowering of the crystal symmetry is observed from cubic Pm 3 ¯ m (x=0.1 and 0.2) to tetragonal I4/mcm (x=0.3 and 0.4), and finally to monoclinic I12/c1 (x=0.5). Low-temperature structural and magnetic measurements show a ferromagnetic ordering with the maximum Curie temperature near 290 K at x=0.2.

LaxSr1−xMnO2.6+δ (x=0.1–0.4) compounds have been obtained by low-temperature annealing of stoichiometric materials in hydrogen. La0.1Sr0.9MnO2.6+δ (δ=0.15) and La0.3Sr0.7MnO2.6, tetragonal (P4/m), and La0.2Sr0.8MnO2.6, pseudo-tetragonal monoclinic (P2/m), structures are isostructural with oxygen-vacancy-ordered Sr5Mn5O13 ( a = b ≈ 5 a P , c≈aP). La0.4Sr0.6MnO2.6 shows cubic perovskite structure with disordered oxygen vacancies. In the vacancy-ordered (LaxSr1−x)5Mn5O13 phases four out of five Mn cations are Mn3+ and show a typical Jahn-Teller elongated pyramidal coordination while the fifth one Mn(4−5x)+, in octahedral environment, shows decreasing formal charge from Mn4+ (x=0) to Mn2.5+ x=0.3. This unusual selective doping of the octahedral site produces structural strain due to increasing size of the Mn(4−5x)+ and, in the case of (La0.2Sr0.8)5Mn5O13, the unusual compressed octahedral arrangement of oxygen atoms around it. The coordination geometry implies that either the d x 2 - y 2 orbital is occupied, which would be a rare example of inverted occupancy of eg orbitals in manganites, or that disordered Mn3+ apically elongated MnO6 octahedra are present with normal electronic configuration d t 2 g 3 d x 2 - y 2 0 d z 2 1 , and the observed bond distances are the average of the long and intermediate in-plane Mn–O bonds. Several structural features favor the second case.

Bulk SrMnO {sub x} samples with oxygen contents 2.5{

The crystal and magnetic structures of the perovskites LuBaCuFeO5+δ and TmBaCuFeO5+δ have been studied in the temperature range 2–170 K by neutron powder diffraction. The best fit using the Rietveld method is obtained for the acentric tetragonal space group P4 mm, with lattice constants a=3.774(1) A, c=7.474(2) A and a=3.7812(2) A, c=7.4854(4) A, for LuBaCuFeO5+δ and TmBaCuFeO5+δ, respectively (T=2 K). The lattice parameters of the unit cell of the magnetic structure for these samples are aM=2a and cM=2c, with a magnetic propagation vector k=( 1 2 , 1 2 , 1 2 ). A commensurate magnetic superstructure is detected by the presence of satellites surrounding the ( 1 2 , 1 2 , 1 2 ) magnetic peak at d∼5.1 A, determined by cMcomm.=8c. This superstructure could evolve at T>170 K to a distribution of commensurate and even incommensurate superstructures. A transition to a simple antiferromagnetic structure occurs at T2=303(3) K for LuBaCuFeO5+δ. Evidence of a strong spin freezing effect at T1=14.0(5) K is provided through DC-susceptibility measurements.

LaBaCuFeO5+δ (LaBCFO) exhibits an irreversible magnetic behavior below T=68(3) K. The local structure around the Cu and Fe atoms studied by EXAFS reveals distortions in the internal shells of the coordination polyhedra of these atoms. A magnetic model could be satisfactorily refined from neutron powder diffraction data, with a magnetic unit cell with lattice parameters related to the structural constants as a M =3a/ 2 , b M =b/ 2 and cM=c/2. This model introduces the existence of randomly distributed magnetic centers in the structure, in agreement with the irreversibility observed by the DC susceptibility measurements. The oxygen disorder including vacancies and the shift in the position of the non-stoichiometric oxygen atoms produced by the imperfect La/Ba replacement in the packing are considered to be key for the magnetic behavior of the LaBCFO.

The crystal structure of LaBaCuFeO 5+ δ is determined by neutron powder diffraction at 15 K and the structure and magnetic properties of the La 1− x Pr x BaCuFeO 5+ δ system are studied by AC-susceptibility measurements and RT 57 Fe Mossbauer spectroscopy. The best fit using the Rietveld method is obtained for an orthorhombic model in space group I mmm with unit cell parameters a =5.5586(8) A, b =5.5550(9) A and c =7.8155(2) A. The main feature of this model is a disordered structure where the oxygen atom vacancies play an important role. The magnetic susceptibility in the La 1− x Pr x BaCuFeO 5+ δ system is studied and T f , μ eff and Θ are determined. Mossbauer spectra provide information relative to the iron electronic state and environment. They support the hypothesis of the key role that the oxygen atom positions play in the magnetic properties of the system by affecting the superexchange interactions in the network.

The synthesis, characterization and single crystal X-ray structure of three compounds of general formula HgI2R (R = phen[1], dmph [2] and bpy[3]) are presented. The crystal data for the three compounds are: [1], triclinic, space group P\(\bar 1\) (#2) a = 7.902(2), b = 9.479(2), c = 10.002(2) A, α = 91.45(2), β = 111.34(2), γ = 100.82(2)° [2]: monoclinic, space group C2/c (#15) a = 15.670(3), b = 11.640(2), c = 9.730(2) A, β = 114.57(3)° [3]: triclinic, space group P1¯ (#2) a = 9.472(1), b = 9.507(1), c = 9.023(1) A, α = 98.46(1), β = 102.89(1), γ = 119.62(1)°. Compounds [1] and [2] are monomers, with highly distorted tetrahedral environments around Hg. In [3], instead, there is a significant intermolecular I···Hg interaction leading to the formation of softly bound dimers linking two pentacoordinated cations. The structure is compared with related ones in the literature.

The presence of layers of corner-sharing square CuO 4 units is a common structural feature of the superconducting copper oxide ceramics. There are three closely related structure types with stoichiometry (RE) 2 CuO 4 , each containing isolated sheets of fourfold (T' structure), fivefold (T* structure) or sixfold (T structure) Cu-O coordination. For the longest rare earth cation (La), (RE) 2 CuO 4 crystallizes in a slightly distorted K 2 NiF 4 T structure. Change of the lanthanide ion from La 3+ to Pr 3+ or Nd 3+ leads to the closely related structure called T' structure (8). This is due to the intermediate size of the rare earth ion in the range (Pr-Gd). The relative simplicity of these rare earth systems allows us to examine how structure is related to ionic size effects and cation ordering. The study of the solid solubility of La 2 CuO 4 (T) and Nd 2 CuO 4 (T') provides a measure of the relative stabilities of these structural types. This work reports the crystal structure of the La 2-x-y Nd y Sr x CuO 4 (x = 0.1, y = 0.1, 0.3), determined by neutron powder diffraction (T = 10 K, RT), with data obtained at Studsvik Neutron Research Laboratory (Sweden). These specimens crystallize in the Cmca space group, showing the T structure and thus the solubility of Nd in this network.

The title compound, C13H20O3, crystallizes as a racemic mixture in which the two enantiomeric forms of the mol­ecule are related by an inversion center. The crystal structure confirms the one proposed on the basis of spectroscopic data and provides the information required to assign the relative stereochemistry of the chiral centers of the mol­ecule. The crystal packing is directed by intermolecular hydrogen bonds and short intramolecular C—H⋯O contacts.

The crystal structure of the adduct, C21H21NO2, of tetra­methyl­purpurogallin with nitro­so­benzene is reported. The compound exhibits a [3.2.2] bicyclic system corresponding to two seven-membered rings and one six-membered ring in distorted chair, boat and twist–boat conformations, respectively. One intramolecular and two intermolecular hydrogen bonds direct the packing and stabilize the mol­ecule.

A series of barium substituted La{sub 0.5}Sr{sub 0.5-x}Ba{sub x}MnO{sub 3} materials has been synthesized and investigated using neutron powder diffraction. We show that Ba substitution suppresses the low-temperature orbital ordering that has been previously observed in La{sub 0.5}Sr{sub 0.5}MnO{sub 3}, and demonstrate the evolution of the magnetic and nuclear structures as a function of increasing Ba content. All our samples exhibit paramagnetic and ferromagnetic properties near room temperature with the ferromagnetic structures described as I4/mc{sup '}m{sup '} and P4/mm{sup '}m{sup '} for x=0, 0.1, and 0.2 and x=0.3, 0.4, and 0.5, respectively. The Mn magnetic moments align ferromagnetically in the direction of the c axis with no evidence for any spin canting. The effects of A-site ionic size, size variance, and strains in the lattice on the ferromagnetic ordering temperature, T{sub C}, are discussed and compared with other members of the general La{sub 0.5}(Ca,Sr,Ba){sub 0.5}MnO{sub 3} series. Depending on the substitution path, the relationship between T{sub C} and is either near constant or looks like an inverted parabola. Finally, details of the magnetic, resistive, structural, and interatomic properties are presented.

The structure and magnetic properties of the compound $\mathrm{La}\mathrm{Ba}\mathrm{Cu}\mathrm{Co}{\mathrm{O}}_{5+\ensuremath{\delta}}$ have been studied for the non-stoichiometric oxygen concentration $\ensuremath{\delta}\ensuremath{\approx}0.6$. The structure is pseudo-cubic with a tripled perovskite unit cell. The crystal structure was determined by a combined Rietveld fit to neutron and synchrotron x-ray powder diffraction data in the orthorhombic $Pmmm$ space group, with cell parameters $a=3.9223(3)\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, $b=3.9360(3)\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, $c=11.7073(8)\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, and $V=180.74(2)\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{3}$ (room temperature). Antiferromagnetic ordering of Cu and Co magnetic moments is observed below $205(4)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The magnetic structure with cell ${a}_{M}=2a$, ${b}_{M}=2b$, and ${c}_{M}=2c$, could be described with the Shubnikov space group $Fmm{m}^{\ensuremath{'}}$. The magnetic moments of both equivalent $\mathrm{Cu}∕\mathrm{Co}$ sites were determined at 50 and $170\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ to be $0.83(3){\ensuremath{\mu}}_{B}$ and $0.58(3){\ensuremath{\mu}}_{B}$, respectively, consistent with one unpaired electron per atom. The fit of the intensities to a simple mean field magnetic model appeared to be insufficient to account for the variation of moments at temperatures close to ${T}_{N}$ while a three dimensional Heisenberg model could improve the fit. Susceptibility measurements between 4 and $350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ also show irreversibility below $150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The local environments of Cu and Co were studied by extended x-ray absorption fine structure spectroscopy at both absorption edges. Cu atoms adopt an elongated octahedral or square-based pyramidal oxygen environment which suggests mainly the presence of Cu(II) in the structure. Co adopts different local environments, depending on the electronic and spin states.

The study of oxygen vacancy ordering in the LaxSr1-xMnOy system has shown a strong correlation between Mn formal valence and coordination to oxygen. The Mn2+ was found forming octahedra (Oc) and tetrahedra (Te), Mn3+ octahedra and pyramids (Py) and Mn4+ only octahedra. This tendency was derived from the presence of three kinds of vacancy orderings in the system. For y>2.5 and the average Mnm+ charge of 20.5), brownmillerite-type structures are found with Mn2+/3+ Oc and Mn2+ Te. [1] For 3