Diffraction and DAFS Studies of a Ba4(BaxPt1−x)Pt2O9Twinned Crystal, a Member of the Bap(BaxPt1−x)Ptp−2O3p−3Series

Crystallographic studies of the Ba–Pt–O system have been undertaken using X-ray and electron diffraction techniques. The system is described by means of a Ba_p(Ba_xPt²⁺_1−x)Pt⁴⁺_p−2O_3p−3formula which corresponds to a BaO₃hexagonal based framework with Pt chains, whereprepresents the oxygen deficiency and the presence of both Pt⁴⁺and Pt²⁺cations in the compounds, andxa possible substitution of Pt²⁺by Ba²⁺in trigonal prismatic sites. The structure of a Ba₄(Ba_0.04Pt²⁺_0.96)Pt⁴⁺₂O₉crystal has been solved by using 5548 X-ray difraction reflections collected on a twinned crystal. Refinements were performed with two distinct models: an “average”P321 space group and an “orthorhombic”C2 space group with cell parametersa=17.460(4) Å,b=10.085(2) Å,c=8.614(3) Å. In this structure, two Pt⁴⁺and one Pt²⁺cations are distributed over four Ba planes and form chains along thecaxis, consisting of two face-sharing Pt⁴⁺O₆octahedra connected with one Pt²⁺O₆trigonal prism. A lattice misfit occurs between the rigid barium lattice and the PtO₃chains, giving rise to a composite structure. Twinning and domain configurations are described and taken into account in the refinement. This twinning is related to the presence of Pt²⁺cations, whose positions break the threefold axis symmetry. A diffraction anomalous fine structure (DAFS) study was also performed on this twinned single crystal. Anomalous scattering factorsf′ andf″ for platinum in this crystal were refined near the L_IIIPt absorption edge. They confirm the weak barium occupancy of the trigonal prismataic site and the Pt⁴⁺valence of the octahedral sites. Reflection overlaps, due to twinning, flatten the DAFS sensitivity to Pt atoms in the prismatic sites and did not allow their clear valence determination, but Pt–O bond lengths agree with the presence of Pt²⁺cations at the center of prismatic faces. Electron diffraction patterns of powders having slightly different composition show a continuous evolution of incommensurate Bragg peaks and a weak correlation between the PtO₃chains. They also confirm the composite nature and the one-dimensionality of the Ba_p(Ba_xPt²⁺_1−x)Pt⁴⁺_p−2O_3p−3series, which can produce highly anisotropic physical properties.     

Sodium “stuffed” Ba2−xSrxFe4O8 ferrites: new cationic conductors

Sodium insertion in the tetrahedral layer structure of the ferrites Ba_2−xSr_xFe₄O₈ was performed by solid state reaction at 1220 K in air. Superstoichiometric oxides with the actual formula (Ba_2−xSr_x)_1−y/4Na_yFe₄O₈—y0.56; 0.60Ba/Sr1.67—were characterized by X-ray and neutron powder diffraction. The hexagonal unit-cell volume shows an increasing dependence on the sodium insertion when the Ba/Sr ratio reaches the largest values. The marked expansion of the c parameter is the likely signature of the location of the inserted sodium cations within the interlayer space. One-half of the sodium cations partly sits on the Sr(Ba) sites in octahedral coordination and the other half occupies extra octahedral and tetrahedral sites. ac conductivity measurements point to a cationic conductivity whose thermally activated regime—E_a 0.7 eV—evidenced from 570 K, is unsensitive to the sodium content. The bottleneck of the 2D sodium mobility regards the crossing of the oxygen triangular faces shared by the different polyhedra within the interlayer space.     

A structural model for barium platinum oxide,Ba3Pt2O7

A single crystal study of Ba₃Pt₂O₇ shows that the structure tolerates a variable composition which can be written Ba₃Pt_2+xO_7+2x. The crystal studied has a hexagonal cell of dimensions a = 10.108 ± 0.006 Å and c = 8.638 ± 0.009 Å, and a probable space group $\text{P}\text{6}\text{2c, Z = 4}$. The density determined by water displacement is 7.99 g/cm³; the theoretical density for Ba₃Pt₂O₇ is 7.94 g/cm³. The structure was determined from the set of 401 observed independent reflections obtained from 5189 reflections measured by automated counter methods. Refinement on F was carried to a conventional R of 8.0%. The structure has barium-oxygen layers with an essentially four-layer stacking sequence of the double hexagonal (ABAB) type. Platinum is found mainly in face-sharing octahedra, but is also distributed over some sites in which the coordination is nearly square planar and other sites in which the coordination is trigonal prismatic with three PtO bond lengths of 2.00 Å and three long PtO distances of 2.65 Å. The platinum with planar coordination is 0.08 Å from the plane of the four oxygen atoms.     

New complex oxides of the A3n+3mA′nB3m+nO9m+6n family: Ba6A′Mn4O15 (A′=Mg, Ni)

Complex oxides Ba₆AMn₄O₁₅, where A=Mg (I) and Ni (II), belonging to the homologous series A_3n+3mA′_nB_3m+nO_9m+6n (n=1, m=1) were obtained by solid state reaction method from Ba carbonate and oxides MgO, NiO, MnO₂. Both new oxides are incommensurate. Their crystal structures were interpreted as composite ones with two subcells: a=10.042(3) Å, c₁=4.318(2) Å, c₂=2.565(1) Å, c₁/c₂=1.6834 for (I) and a=10.044(3) Å, c₁=4.308(2) Å, c₂=2.551(1) Å, c₁/c₂=1.6887 for (II). Magnetic susceptibility measurements in the range 2–850 K revealed antiferromagnetic correlations in Ba₆MgMn₄O₁₅ (T_N=7 K) and a pseudo-square-planar environment of some Ni²⁺ cations in Ba₆NiMn₄O₁₅.     

A niobium phosphate with a tunnel structure: Ca0.5+xCs2Nb6P3O24

A new niobium phosphate, Ca_0.5+xCs₂Nb₆P₃O₂₄ has been isolated. It crystallizes in the R32 space group, with the following parameters of the hexagonal cell: a_H = 13.379 Å, c_H = 10.371 Å. The determination of the structure by a single crystal X-ray diffraction study shows that its host lattice [Nb₆P₃O₂₄]_∞ can be described as the assemblage of mixed chains [Nb₂PO₁₃]_∞ running along c_H in which one PO₄ tetrahedron alternates with two NbO₆ octahedra. This framework delimits huge tunnels where the cesium cations are located and cages formed by [Nb₆P₃O₃₆] units occupied by calcium. The most striking feature of this framework deals with its similarity with the hexagonal tungsten bronze of Magnéli (HTB). The latter is discussed here by considering the stacking along c of [Nb₂PO₈]_∞ layers whose geometry is closely related to that of the HTBs. The possibility of nonstoichiometry leading to a mixed valency of niobium is considered.     

Unusual Metal–Metal Bonding in a Dinuclear Pt–Au Complex: Snapshot of a Transmetalation Process

The dinuclear Pt–Au complex [(CNC)(PPh₃)Pt Au(PPh₃)](ClO₄) ( 2 ) (CNC=2,6‐diphenylpyridinate) was prepared. Its crystal structure shows a rare metal–metal bonding situation, with very short Pt–Au and Au–C_ipso(CNC) distances and dissimilar Pt–C_ipso(CNC) bonds. Multinuclear NMR spectra of 2 show the persistence of the Pt–Au bond in solution and the occurrence of unusual fluxional behavior involving the [Pt^II] and [Au^I] metal fragments. The [Pt^II]??? [Au^I] interaction has been thoroughly studied by means of DFT calculations. The observed bonding situation in 2 can be regarded as a model for an intermediate in a transmetalation process.     

Synthese et propriétés de conduction ionique des phases Li8−2xCaxCeO6 (0 < x ≤ 0,5) et Li6CaCeO6

The solid solution Li_8−2xCa_xCeO₆ (0 < x ≤ 0,5) and the definite phase Li₆CaCeO₆ have been obtained at 800°C through a study of Li---Ca---Ce---O system. Electrical measurements on the doped phases Li^tetr.₆ [Li_2-2xCa_xCe□]^oct.O₆ show that the conductivity varies slightly with the creation of vacancies in the octahedral layers. This result unambiguously confirms the following diffusion mechanism: the conduction is assumed essentially by lithium ions located in the tetrahedral layers. The compound Li₆CaCeO₆ is isostructural with Li₆In₂O₆. The cell is trigonal, Å, c = 10,603 Å, c/a = 1,058₇, and Z = 6. This new quaternary phase, which belongs to the same structural family of oxides of the type Li₈MO₆, either pure or doped with calcium, may be represented by the formula Li^tetr.₆[Ca Ce□]^oct.O₆. Electrical and structural data are correlated for this compound.     

Crystal growth of new perovskite and perovskite related iridates: Ba3LiIr2O9, Ba3NaIr2O9, and Ba3.44K1.56Ir2O10

Single crystals of Ba₃LiIr₂O₉, Ba₃NaIr₂O₉, and Ba_3.44K_1.56Ir₂O₁₀ were grown from hydroxide fluxes. Ba₃LiIr₂O₉ and Ba₃NaIr₂O₉ form in the 6H–BaTiO₃ or triple perovskite structure, which is derived from the hexagonal and cubic stacking of [AO₃] layers. The structure contains face-sharing Ir₂O₉ octahedra pairs, which are connected via corner shared LiO₆ (NaO₆) octahedra. Both compounds crystallize in the space group P6₃/mmc, Z=2, with a=5.7804(4) and c=14.302(1) and a=5.866(4) and c=14.596(1) for the Li and Na member, respectively. The structure of Ba_3.44K_1.56Ir₂O₁₀ is derived from the stacking of [AO₃] and mixed [A₂O] layers, and is an n=3 member of the [A_nM_n−1O_3n][A₂O] family of hexagonal perovskite related oxides. The structure of Ba_3.44K_1.56Ir₂O₁₀ consists of (Ba₃Ir₂O₉) slabs separated by [(Ba,K)₂O] layers and is isostructural with Ba₅Ru₂O₁₀. The (Ba₃Ir₂O₉) slabs contain isolated, face-sharing Ir₂O₉ octahedra pairs. The compound crystallizes in the space group P6₃/mmc, Z=2, with a=5.91330(1) Å and c=18.1792(7) Å. The magnetic moments determined from the temperature dependence of the magnetic susceptibility are low for all three oxides, which is thought to be due to a combination of spin–orbit coupling and strong exchange interactions within the iridium octahedra pairs.     

Ba3N – a New Binary Nitride of an Alkaline Earth Metal

Reacting Ba and N₂ in the stoichiometric ratio 6 : 1 at 670 K, homogenizing the product at 570 K in the presence of Na and subsequently distilling off the Na yields Ba₃N. This new subnitride decomposes into Ba₂N and Ba at 830 K. Its structure represents a hexagonal rod packing of Ba_6/2N chains (anti-TiI₃ type, space group P6₃/mcm; a = 764.18(2) pm, c = 705.01(5) pm; Ba in 6 g with x = 0.2721(2), N in 2 b). The peculiarity of a very spaceous packing of these rods is addressed and discussed as possibly due to a quantum size effect.     

Polarized emission from Ba[Pt(CN)4]·4H2O single crystals under high pressure

The emission spectra of single crystal Ba[Pt(CN)₄]·4H₂O were measured from 0 to 23 kbar for the two electronic transitions which are polarized with Ec and E;c. They exhibit a red-shift of −280 cm⁻¹/kbar and −195 cm⁻¹/kbar, respectively. 3he red-shift is explained by a pressure induced reduction of the intermolecular separation R in the direction of the linear chain (c-axis). The emission energies obtained at different pressures are compared with the results under normal conditions for various Me[Pt(CN)₄]·xH₂O salts (with different R). The close analogy between these two methods of R-reduction supports the importance of one-dimensional interaction for the interpretation of electronic properties of the tetracyano-platinates. Ba[Pt(CN)₄]·4H₂O shows a structural transition region in the pressure range studied here.     

Hydrothermal Synthesis and Crystal Structure of a New BariumVanadium Bronze Ba1+xV8O21 with a Tunnel Structure

A barium vanadium bronze Ba_1+xV₈O₂₁ has been hydrothermally synthesized and structurally characterized. Hydrothermal treatment of a suspension of VO₂ powders in Ba(NO₃)₂ solution at 350°C yielded a fibrous brown compound having nonstoichiometric composition Ba_1+xV₈O₂₁ (x=0.13). Single-crystal X-ray diffractometry revealed the monoclinic system C2/m with a=15.144(6), b=3.596(4), c=14.972(3) Å, β=90.08(3)°, and Z=2, with the refinement based on 2021 reflections with I>3σ(I) converged to R=0.054 and R_w=0.046. A new tunnel-type bronze structure was disclosed in which VO₆ octahedra and VO₅ trigonal bipyramids form a V–O framework with a tunnel cavity running along [010]. The Ba atom partially occupies the tunnel site with more than half occupancy of 56.6%, which causes displacement of the Ba atom and further displacement of V and O atoms along the tunnel axis. Ba_1+xV₈O₂₁ is the first tunnel-type barium vanadium bronze whose structure has been fully determined.     

The Phase Relations in the System In2O3–TiO2–MgO at 1100 and 1350°C

The phase relations in the system In₂O₃–TiO₂–MgO at 1100 and 1350°C are determined by a classical quenching method. In this system, there are four pseudobinary compounds, In₂TiO₅, MgTi₂O₅ (pseudobrookite type), MgTiO₃ (ilmenite type), and Mg₂TiO₄ (spinel type) at 1100°C. At 1350°C, in addition to these compounds there exist a spinel-type solid solution Mg_2−xIn_2xTi_1−xO₄ (0≤x≤1) and a compound In₆Ti₆MgO₂₂ with lattice constants a=5.9236(7) Å, b=3.3862(4) Å, c=6.3609(7) Å, β=108.15(1)°, and q=0.369, which is isostructural with the monoclinic In₃Ti₂FeO₁₀ in the system In₂O₃–TiO₂–MgO. The relation between the lattice constants of the spinel phase and the composition nearly satisfies Vegard's law. In₆Ti₆MgO₂₂ extends a solid solution range to In₂₀Ti₁₇Mg₃O₆₇ with lattice constants of a=5.9230(5) Å, b=3.3823(3) Å, c=6.3698(6) Å, β=108.10(5)°, and q=0.360. The distributions of constituent cations in the solid solutions are discussed in terms of their ionic radius and site preference effect.     

Influence of the Mg-content on the cation distribution in cubic MgxFe3−xO4 nanoparticles

The influence of the Mg-content on the structural and magnetic properties of cubic Mg_xFe_3−xO₄ nanoparticles prepared by combustion reaction was investigated using X-ray diffraction, transmission electron microscopy (TEM), Mössbauer spectroscopy, and Raman spectroscopy. Lattice parameter, nanoparticle size, and cation (Mg²⁺, Fe³⁺) distribution were quantified as a function of the Mg-content in the range 0.5≤x≤1.5. We found a mixed-like spinel structure at the smaller x-value end whereas the inverse-like spinel structure dominates samples with larger x-values. Moreover, in the x-value range investigated (0.5≤x≤1.5) we found no change in the quadrupole splitting and isomer shift values, though the hyperfine field decreases as the x-value increases. The splitting of the A_1g Raman mode was used to both quantify the Mg²⁺/Fe³⁺ contents in the tetrahedral site and obtain the cation distribution in the Mg_xFe_3−xO₄ structure. The cation distribution obtained from the Raman data is in very good agreement with the cation distribution obtained from the Mössbauer data.     

Magnetic structure of the UCuxSi2−x system

Neutron powder diffraction experiments were performed on selected compositions of the UCu_xSi_2−x system exhibiting an interesting magnetic phase diagram towards the composition: spin fluctuation behaviour for x<0.49, ferromagnetism for 0.49≤x<0.80, spin glass state for 0.80<x<0.92 and finally antiferromagnetism for 0.92<x≤0.96. At 1.5 K, the compounds UCu_0.49Si_1.51 (hexagonal AlB₂ modification) and UCu_0.65Si_1.35 show a collinear ferromagnetic structure where the uranium magnetic moments equal to 1.1(1) and 2.5(1)μ_B, respectively, are aligned in the basal plane of the [U₆] trigonal prisms. On the contrary, UCu_0.96Si_1.04 adopts a non-collinear antiferromagnetic structure similar to that observed for UCuSn. Moreover, the study confirms the absence of long range magnetic order for UCu_0.90Si_1.10.     

Crystal chemistry, modulated structure, and electrical conductivity in the oxygen excess scheelite-based compounds La1−xThxNbO4+x/2 and LaNb1−xWxO4+x/2

For La_1−xTh_xNbO_4+x/2, three phases with broad homogeneity regions occur, for 0.075 ≤ x ≤ 0.37, 0.41 < x < 0.61, and 0.65 ≤ x ≤ 0.74. All are related to the scheelite structure type, with at least the first exhibiting an incommensurate structural modulation. An analogous structurally modulated phase was found for LaNb_1−xW_xO_4+x/2 for 0.11 ≤ x ≤ 0.22. Additional phases occur at La_0.2Th_0.8NbO_4.4 and LaNb_0.4W_0.6O_4.3. The electrical conductivity and the direction and wavelength of the structural modulation have been characterized for the La_1−xTh_xNbO_4+x/2 phase with 0.075 ≤ x ≤ 0.37.     

Structure and Magnetism of Pr1−xSrxFeO3−δ

Crystal structure, redox, and magnetic properties for the Pr_1−xSr_xFeO_3−δ solid-solution phase have been studied. Oxidized samples (prepared in air at 900°C) crystallize in the GdFeO₃-type structure for 0≤x≤0.80, and probably in the Sr₈Fe₈O₂₃-type (unpublished) structure for x=0.90. Reduced samples (containing virtually only Fe³⁺) crystallize as the perovskite aristotype for x=0.50 and 0.67 with randomly distributed vacancies. The Fe⁴⁺ content increases linearly in the oxidized samples up to x≈0.70, whereupon it stabilizes at around 55%. Antiferromagnetic ordering of the G type is observed for oxidized samples (0≤x≤0.90) which show decreasing Néel temperature and ordered magnetic moment with increasing x, while the Néel temperature is nearly constant at 700 K for reduced samples. Electronic transitions for iron from an average-valence state via charge-separated to disproportionated states are proposed from anomalies in magnetic susceptibility curves in the temperature ranges 500–600 K and 150–185 K.     

Kinetics and catalysis by NaY entrapped Pt carbonyl clusters in the CO+NO reaction

[Pt₁₂(CO)₂₄]^2–/NaY and [Pt₉(CO)₁₈]^2–/NaY exhibited much higher activities in the CO+NO reaction at 473 K compared with Pt/Al₂O₃. Kinetic study andin-situ FTIR results suggest that NO adsorption is the rate-limiting step in the CO+NO reaction on intrazeolite Pt carbonyl clusters.     

π–π Dimerization of a mono(pyridyl–imine) platinum(II) chelate

The cation of the title complex salt, chlorido{2,2‐dimethyl‐N‐[(E)‐1‐(pyridin‐2‐yl)ethylidene]propane‐1,3‐diamine}platinum(II) tetrafluoridoborate, [PtCl(C₁₂H₁₉N₃)]BF₄, exhibits a nominally square‐planar Pt^II ion coordinated to a chloride ion [Pt—Cl = 2.3046 (9) Å] and three unique N‐atom types, viz. pyridine, imine and amine, of the tridentate Schiff base ligand formed by the 1:1 condensation of 1‐(pyridin‐2‐yl)ethanone and 2,2‐dimethylpropane‐1,3‐diamine. The cations are π‐stacked in inversion‐related pairs (dimers), with a mean plane separation of 3.426 Å, an intradimer Pt...Pt separation of 5.0785 (6) Å and a lateral shift of 3.676 Å. The centroid (Cg) of the pyridine ring is positioned approximately over the Pt^II ion of the neighbouring cation (Pt...Cg = 3.503 Å).     

Ba6(MN4)N2–x (M = MoVI/TaV), a Subvalent Nitridometalate with Perovskite‐like Crystal Structure

The subvalent nitridometalate Ba₆[(Mo_1–xTa_x)N₄]N_0.86 was prepared from mixtures of Mo powder with Ba, Na, and Ba₂N at 600 °C in Ta ampoules. It crystallizes in space group Cmcm with a = 11.672(3), b = 10.177(2) and c = 10.8729(19) Å. Its crystal structure exhibits an orthorhombically distorted Perovskite topology with [Ba₆N] building units forming the ReO₃‐type lattice via common vertices, and the nitridometalate anions occupying half of the available distorted cuboctahedral interstices. [MN₄] anions show statistically mixed occupancy of M by Mo^VI and Ta^V. They show no notable deviation from nitridometalate anions in known ionic nitridomolybdates and ‐tantalates, and the metrics of the [Ba₆N] octahedra correspond to those found in similar subvalent compounds. The nitrogen atom position centering the [Ba₆N] octahedra is underoccupied. Band structure calculations corroborate the subvalent character of the compound and the two individual anionic structural building units.     

Phase separation in the spin-state transition system of La1−xBaxCoO3

The magnetic and electric transport properties of La_1−xBa_xCoO₃ (0<x≤0.50) have been studied systematically. Two effects of substitution divalent ions on the spin-state transition of Co³⁺ have been differentiated for the substitution of Ba²⁺ for La³⁺ in La_1−xBa_xCoO₃. The first is the transition from low-spin state to high-spin state due to lattice expansion, and the second is the transition from low-spin state to intermediate-spin state caused by the strong hybridization between ligand (oxygen) 2p and Co 3d orbital with introduction of holes in the oxygen 2p orbital. Based on the two different spin-state transition mechanisms and experimental results, a phase separation model has been developed and a very detailed magnetic and electric phase diagram of La_1−xBa_xCoO₃ has been constructed.