Ab initio structure determination of new compound Li4CaB2O6

A new compound, Li₄CaB₂O₆, has been synthesized by solid-state reaction and its structure has been determined from powder X-ray diffraction data by direct methods. The refinement was carried out using the Rietveld methods and the final refinement converged with R_p=10.4%, R_wp=14.2%, R_exp=4.97%. This compound belongs to the orthorhombic space group Pnnm, with lattice parameters a=9.24036(9) Å, b=8.09482(7) Å, and c=3.48162(4) Å. Fundamental building units are isolated [BO₃]³⁻ anionic groups, which are all parallel to the a-b plane stacked along the c-axis. The Ca atoms are six-coordinated by the O atoms to form octahedral coordination polyhedra, which are joined together through edges along the c-axis, forming infinitely long three-dimensional chains. The Li atoms have a four-fold and a five-fold coordination with O atoms that lead to complex Li-O-Li chains that also extend along the c-axis. The infrared spectrum of Li₄CaB₂O₆ was also studied, which is consistent with the crystallographic study.     

Über Sauerstoffperowskite mit fünf- und vierwertigem Iridium Verbindungen vom Typ Ba2B3+Ir5+O6 und Ba3B3+Ir4,5+2O9

Perovskites with pentavalent iridium of type Ba₂B³⁺Ir⁵⁺O₆ are for B³⁺ = La, Nd, Sm, Gd, Dy, Y cubic and with B³⁺ = In hexagonal (6 L structure of BaTiO₃ type; sequence (hcc)₂). According to the intensity calculations of powder patterns for Ba₃SmIr₂O₉ and Ba₃YIr₂O₉ the new series Ba₃B³⁺Ir₂O₉ (B³⁺ = Sm, Eu, Gd, Dy, Ho, Yb, Sc, Y, In; mean oxidation state of iridium + 4.5) crystallize in a hexagonal 6 L structure of BaTiO₃ type (space group $\text{P6}{}_3\text{mmc}$; sequence (hcc)₂). The intensity-related R′ value is 8.6% for B³⁺ = Sm and 10.0% for Y. In the octahedral net the double groups of face-connected octahedra are occupied by the iridium atoms, which are dislocated from their ideal positions such that the IrIr distance has increased (2.72₀ Å (Sm) or 2.63₂ Å (Y)). The ir spectra are reported and discussed in connection with the corresponding factor group analysis.     

Synthesis and crystal structure of gallosilicate- and aluminogermanate tetrahydroborate sodalites Na8[GaSiO4]6(BH4)2 and Na8[AlGeO4]6(BH4)2

Tetrahydroborate enclathrated sodalites with gallosilicate and aluminogermanate host framework were synthesized under mild hydrothermal conditions and characterized by X-ray powder diffraction and IR spectroscopy. Crystal structures were refined in the space group P-43n from X-ray powder data using the Rietveld method. Na₈[GaSiO₄]₆(BH₄)₂: a=895.90(1) pm, V=0.71909(3)×10⁻⁶ nm³, R_P=0.074, R_B=0.022, Na₈[AlGeO₄]₆(BH₄)₂: a=905.89(2) pm, V=0.74340(6)×10⁻⁶ nm³, R_P=0.082, R_B=0.026. The tetrahedral framework T-atoms are completely ordered in each case and the boron atoms are located at the centre of the sodalite cages. The hydrogen atoms of the enclathrated anions were refined on x, x, x positions, restraining them to boron-hydrogen distances of 116.8 pm as found in NaBD₄.The IR-absorption spectra of the novel phases show the typical bands of the tetrahedral group as found in the spectrum of pure sodium boron hydride.The new sodalites are discussed as interesting -containing model compounds which could release pure hydrogen.     

Thermoelectric properties of some metal borides

Polycrystalline AlMgB₁₄ and some hexaborides (CaB₆, SrB₆, YbB₆, SmB₆, and CeB₆) were synthesized to examine their thermoelectric properties. Single phase of orthorhombic AlMgB₁₄, which contains B₁₂ icosahedral clusters as building blocks, was obtained at sintering temperatures between 1573 and 1823 K. Seebeck coefficient (α) and electrical conductivity (σ) of the phase were about 500 μV/K and 10⁻¹ 1/Ω m at room temperature, respectively. These values are comparable to those of metal-doped β-rhombohedral boron. On the other hand, metal hexaborides with divalent cation possessed large negative α ranging from −100 to −270 μV/K at 1073 K. Calculated power factors of CaB₆ and SrB₆ exceeded 10⁻³ W/K² m within the entire range of temperature measured. As a result, they can be thought as promising candidates for n-type thermoelectric material.     

Multianvil high-pressure/high-temperature preparation, crystal structure, and properties of the new oxoborates Dy4B6O14(OH)2 and Ho4B6O14(OH)2

This paper reports about two new hydrogen-containing rare-earth oxoborates RE₄B₆O₁₄(OH)₂ (RE=Dy, Ho) synthesized under high-pressure/high-temperature conditions from the corresponding rare-earth oxides, boron oxide, and water using a Walker-type multianvil equipment at 8 GPa and 880 °C. The single crystal structure determination of Dy₄B₆O₁₄(OH)₂ showed: Pbcn, a=1292.7(2), b=437.1(2), , Z=2, R1=0.0190, and wR2=0.0349 (all data). The isotypic holmium species revealed: Pbcn, a=1292.8(2), b=436.2(2), , Z=2, R1=0.0206, and wR2=0.0406 (all data). The compounds exhibit a new type of structure, which is built up from layers of condensed BO₄-tetrahedra. Between the layers, the rare-earth cations are coordinated by 7+2 oxygen atoms. Furthermore, we report about temperature-resolved in situ powder diffraction measurements, DTA/TG, and IR-spectroscopic investigations into RE₄B₆O₁₄(OH)₂ (RE=Dy, Ho).     

Synthesis, crystal structure and magnetic properties of new indium rhenium and scandium rhenium oxides, In6ReO12 and Sc6ReO12

The new complex indium rhenium and scandium rhenium oxides, In₆ReO₁₂ and Sc₆ReO₁₂, have been synthesized as single phases in sealed silica tubes and by high-pressure high-temperature syntheses, and their crystal structures have been determined by single crystal X-ray diffraction.The compounds crystallize in a rhombohedral structure related to the distorted fluorite structure like Ln₆ReO₁₂ for some rare earth elements, S. G.: R-3, Z=3, a_H= 9.248(2) Å, c_H=8.720(2) Å for Sc₆ReO₁₂ and a_H=9.492(1) Å, c_H=8.933(1) Å for In₆ReO₁₂. A maximum in magnetization is observed for Sc₆ReO₁₂ at T(M_max)=1.89(2) K, whereas ferromagnetic ordering is found for In₆ReO₁₂ by a pronounced increase in the temperature dependence of magnetization at T_C=7.5(5) K. The magnetic moment per rhenium ion in In₆ReO₁₂ and Sc₆ReO₁₂ is 0.84(1) and 0.65(1) μ_B, respectively, derived from the paramagnetic regions.     

Synthesis, Structure, and Superconductivity in Be1.09B3

The compound Be_1.09B₃ was prepared by arc-melting of the elemental constituents. The structure of single crystals taken from the arc-melted boule was determined from single-crystal X-ray data (T=120 K) and is hexagonal, having space group P6/mmm, and lattice parameters a=9.7738(7) Å and c=9.5467(6) Å, R=0.047. The structure consists of a hexagonal array of boronicosahedra, nonicosahedral B₁₂ cages, and B₁₈ cages. Stacked hexagonal layers of boron atoms, hexagons formed by B and Be, and equilateral triangles of boron atoms disordered by a 60° rotation exist along a 6-fold axis down the [001] direction. A superconducting transition at 0.72 K is clearly indicated by resistivity measurements.     

Ferromagnetic ordering in ThSi2 type CeAu0.28Ge1.72

The compound CeAu_0.28Ge_1.72 crystallizes in the ThSi₂ structure type in the tetragonal space group I4₁/amd with lattice parameters a=b=4.2415(6) Å c=14.640(3) Å. CeAu_0.28Ge_1.72 is a polar intermetallic compound having a three-dimensional Ge/Au polyanion sub-network filled with Ce atoms. The magnetic susceptibility data show Curie-Weiss law behavior above 50 K. The compound orders ferromagnetically at ∼8 K with estimated magnetic moment of 2.48 μ_B/Ce. The ferromagnetic ordering is confirmed by the heat capacity data which show a rise at ∼8 K. The electronic specific heat coefficient (γ) value obtained from the paramagnetic temperature range 15-25 K is∼124(5) mJ/ mol K². The entropy change due to the ferromagnetic transition is ∼4.2 J/mol K which is appreciably reduced compared to the value of R ln(2) expected for a crystal-field-split doublet ground state and/or Kondo exchange interactions.     

Direct low-temperature synthesis of RB6 (R=Ce, Pr, Nd) nanocubes and nanoparticles

Rare-earth hexaborides (RB₆, R=Ce, Pr, Nd) nanocrystals were prepared by a facile solid state reaction in an autoclave. Single-crystalline RB₆ nanocubes were fabricated at 500 °C starting from B₂O₃, RCl₃·6H₂O and Mg powder. RB₆ nanoflakes and nanoparticles could be obtained around 400 °C using NaBH₄ as boron resource. XRD patterns show that all of the hexaborides are cubic phase with high crystallinity and high purity and have lattice parameters that are consistent with nearly stoichiometric products. Raman spectra elucidate the active vibrational modes of the hexaborides. The TEM and FESEM images clearly show that the nanocubes have an average size of 200 nm and nanoparticles of 30 nm. Our experiment developed an efficient, simple and low-cost route to prepare RB₆, which could be extended further to the preparation of other rare-earth metal hexaborides.     

Structure and magnetic properties of ScFe6Ga6-type RCo5Ga7 (R=Y, Tb, Dy, Ho and Er)

The structure and magnetic properties of the RCo₅Ga₇ (R=Y, Tb, Dy, Ho and Er) compounds with the ScFe₆Ga₆-type structure have been studied. The stability of RCo₅Ga₇ is closely related with the ratio of the metal radii R_RE/R_(Co,Ga). With R_RE/R_(Co,Ga)?1.36, the compounds can be stabilized in the ScFe₆Ga₆-type structure. The lattice of RCo₅Ga₇ shrinks as the atomic order of R increases, and it is consistent with the lanthanide contraction. The structure analysis based on X-ray diffraction patterns reveals that in the orthorhombic RCo₅Ga₇ (Immm), R occupies the 2a site, and Co enters into the 8k and the 4h sites, and Ga is at the 4e, 4f, 4g, 4h and 8k sites. The interatomic distances and the coordination numbers of RCo₅Ga₇ are provided from the refinement results. The short interatomic distance (less than 2.480 Å) between the Co ions results in the negative magnetic interaction, which does not favor ferromagnetic ordering. The magnetic moment of YCo₅Ga₇ is absent, and RCo₅Ga₇ (R=Tb, Dy, Ho and Er) may have long-range magnetic ordering with the paramagnetic Curie temperature lower than 5 K.     

High-Pressure Synthesis and Crystal Structure of B2S3

Two new high-pressure phases of binary boron-sulfur compounds, B₂S₃-II and B₂S₃-III, were synthesized at 3-6.2 GPa. A single crystal of B₂S₃-III was grown and the structure was determined (tetragonal, space group I4₁/a, a=16.086(2) Å, c=30.488(4) Å; V=7888(1) ų, Z=100, R=3.0% and R_w=2.8% for 3047 observed data [I>3.00σ(I)]. The structure of B₂S₃-III consists of two kinds of macrotetrahedra built up from 20 and 34 BS₄-tetrahedra. These macrotetrahedra connect each other to form an interpenetrating zincblende-type structure by sharing BS₄-tetrahedra at the corners of those. B₂S₃-III is anticipated having a rather disordered structure. From the UV-Vis diffuse reflectance spectrum, the optical band gap of B₂S₃-III was estimated to be 3.7 eV.     

Fluorine-bridged chain compounds as models in magnetochemistry: structures and magnetism of (imidH)2[Fe2oxF6] and [Fe2oxF4(DMSO)4]

The crystal structure of a new Fe(III) dimer obtained by fluorination of FeCl₃ with Me₃SnF in the presence of oxalic acid and crystallization from dimethyl sulfoxide (DMSO) has been determined: [Fe₂oxF₄(DMSO)₄] 1, Space group P2₁/n, Z=2, a=7.259(2), b=11.409(3), c=13.374(2) Å, β=97.26(1), R=4.47%. It shows a tetradentate bridging oxalato, equatorial cis fluorine and axial trans DMSO ligands.From an aqueous solution of FeF₃·3H₂O, oxalic acid, and imidazolium fluoride, crystals of (imidH)₂[Fe₂oxF₆] 2 could be precipitated. Space group Pban, Z=2, a=9.143(2), b=20.837(6), c=3.890(1) Å, R=2.51%. The structure shows anionic chains formed by bridging trans fluorine ligands connected, like in the dimer above, by oxalate anions to form a double chain. The magnetic properties were determined on powders by SQUID measurements. Mössbauer experiments were performed on the S=5/2 Fe³⁺ double chain of (imidH)₂[Fe₂oxF₆], where the anisotropy is of dipolar origin and is therefore very weak. The striking result is the characteristic aspect of two magnetic split spectra below T_N and additionally, the coexistence of a temperature dependent paramagnetic component (doublet) and the magnetic split spectra in the temperature range T_N=14.5 and T_H=40 K. The origin of that unusual behaviour is attributed to nonlinear excitations (magnetic solitons) in systems with small local anisotropy. Consequently, the domain wall width should be large. The subspectrum of the doublet was identified with intraband solitons. The relative intensity of the fast relaxing component increases with increasing temperature as ∝exp(−E_s/kT). From the slope of fractional intensity of the broadened doublet as a function of inverse temperature, the activation energy E_s/k=40(1) K was derived. Considering the results of magnetic susceptibility measurements of the intra-chain exchange constant J/k=−17.3(2) K, we found an anisotropy constant of D/k=0.15(2) K in agreement with our magnetic study. Additionally, parameters as the inter-chain constants J′/k=0.08(2) K and J″/k=0.60(5) K were calculated. Speculatively, from the experimental data of the magnetically split spectra the ratio (domain length/domain wall width) ≈ 2 was estimated at T_N, in agreement with the theoretical expectations. Finally, the results obtained for the double chain of (imidH)₂[Fe₂oxF₆] with weak anisotropy are compared with previously reported Mössbauer experiments on -doped powder of (ND₄)₂MnF₅, inelastic neutron scattering, and magnetic susceptibility measurements on single crystals of (ND₄)₂MnF₅ with strong anisotropy.     

Calorimetric and spectroscopic studies of the critical phase transition in (CH3NH3)2[SnCl6]

(CH₃NH₃)₂[SnCl₆] undergoes a critical phase transition at 154.32 ± 0.06 K with the critical exponents α = 0.36 ± 0.04, α' = 0.19 ± 0.02, the critical entropy ratio 0.062 and the total transition entropy (1.60 ± 0.18) R. Infrared spectral change favors the order-disorder mechanism of the transition proposed from the thermodynamic data.     

Dirac—Fock one-centre calculations. VI. The tetrahedral and octahedral model systems CeH4, ThH4, CrH6, MoH6, WH6, UH6 and (106)H6

Relativistic and non-relativistic Hartree—Fock calculations are reported for the tetrahedral model systems CeH₄ and ThH₄ and the octahedral model systems CrH₆, MoH₆, WH₆, UH₆ and (106)H₆. The effects of relativity on bond strengths and lengths are obtained from fits to a Morse potential. The calculated CrH, MoH and WH bond lengths are comparable to those measured in the organometallic systems. Their relativistic contractions are 0.36, 0.8 and 2.8%, respectively. For the MH_n systems (M = Ti, Zr, Hf, Th, Cr, Mo, W), the calculated MH bond lengths differ in the average from the experimental MX by 16, 39, ?3, 42, 55 and 75 pm for X = Hb(BH₄), C(σ), F, Cl, Br and I, respectively, suggesting a “hydridic” hydrogen covalent radius of 58 pm. A comparison of the bond lengths for CeH₄ and HfH₄ yields the value of 19 pm for the lanthanoid contraction. A corresponding non-relativistic calculation gives 16 pm. Thus the lanthanoid contraction is predominantly a non-relativistic shell-structure effect. A similar comparison of ThH₄ and (104)H₄ or of UH₆ and (106)H₆ predicts an actinoid contraction of 30 pm for compounds of the present type. The fact that WH bonds are stronger than MoH bonds is probably due to relativistic effects. Strong s-p-d hybridization is found for CeH₄ and ThH₄ with only weak f AO contributions. For UH₆ the f AO participation is four times larger and has a double-humped radial distribution suggesting “true” 5f participation in bonding. Adding the 5f:s shortens the bond length by 8 and 22 pm for ThH₄ and UH₆, respectively, also indicating s-p-d-f hybridization for uranium. The 7p radius for Th is larger than the 6d radius and the norm N(7p), of the t₂ MO increases with increasing bond length R. Therefore this t₂ MO causes a potential V(R), that is more attractive than in the case without 7p functions, even at R of the order of 500 pm. Possible connection with hydrogenation catalysis by elements like Th and Ti is discussed.     

Substitution in barium-fluoride apatite: The crystal structures of Ba10(PO4)6F2, Ba6La2Na2(PO4)6F2 and Ba4Nd3Na3(PO4)6F2

The crystal structures of the apatites Ba₁₀(PO₄)₆F₂(I), Ba₆La₂Na₂(PO₄)₆F₂(II) and Ba₄Nd₃Na₃(PO₄)₆F₂ (III) have been determined by single-crystal X-ray diffraction. All three compounds crystallize in a hexagonal apatite-like structure. The unit cells and space groups are: I, a = 10.153(2), c = 7.733(1)Å, $\text{P6}{}_3\text{m}\text{; a = 9.9392(4), c = 7.4419(5)}$Å, $\text{P}\text{6}$; III, a = 9.786(2), c = 7.281(1)Å, $\text{P}\text{3}$. The structures were refined by normal full-matrix crystallographic least squares techniques. The final values of the refinement indicators R_w and R are: I, R_w = 0.026, R = 0.027, 613 observed reflections; II, R_w = 0.081, R = 0.074, 579 observed reflections; III, R_w = 0.062, R = 0.044, 1262 observed reflections.In I, the Ba(1) atoms located in columns on threefold axes, are coordinated to nine oxygen atoms; the Ba(2) sites form triangles about the F site and are coordinated to six oxygen atoms and one fluoride ion. The fluoride ions are statistically displaced ～0.25 Å from the Ba(2) triangles. This displacement of the F ions is analogous to the displacement of OH ion in Ca₁₀(PO₄)₆(OH)₂.The structures of II and III contain disordered cations. In II there is disorder between La and Na in the column cation sites as well as triangle sites. In III, Nd and Na ions are ordered in the column sites, but there is disorder among Ba and the remaining Nd and Na ions in the triangle sites to give an average site population of $\text{2}\text{3}\text{Ba}\text{,}\text{1}\text{6}\text{Nd}\text{,}\text{1}\text{6}\text{Na}$. The coordination of the rare earth ions and Na ions in the ordered column sites are nine and six oxygens, respectively, in accord with the greater charge of the rare earth ions as compared with Na. The F ions in both II and III suffer from considerable disorder in position, and their locations are not precisely known.     

Growth and spectroscopic characterization of Nd:Sr6GdSc(BO3)6 crystal

A crystal of Nd³⁺:Sr₆GdSc(BO₃)₆ with the dimension of φ20×30 mm³ was grown by Czochralski method. The grown crystal was characterized by X-ray diffraction and DSC analysis. The DSC analysis showed that the crystal congruently melt at 1306.7°C. The absorption and emission spectra of Nd³⁺:Sr₆GdSc(BO₃)₆ were investigated. The absorption band at 806 nm has a FWHM of 13 nm. The absorption and emission cross-sections are 2.33×10⁻²⁰ cm² at 806 nm and 1.58×10⁻¹⁹ cm² at 1062 nm, respectively. The luminescence lifetime τ_f is 75 μs at room temperature.     

Synthesis of π-(arene)metallocarboranes containing iron and ruthenium. Crystal structure of 3,1,2-(η6-1,3,5-(CH3)3C6H3)FeC2B9H11

The reaction of bis(arene)iron(II) salts (arene = mesitylene or hexamethylbenzene) or benzenedichlororuthenium(II) dimer with Tl[3,1,2-TlC₂B₉H₁₁] in THF produces neutral, air-stable π-(arene)(Fe, Ru)C₂B₉H₁₁ complexes in low or moderate yields. The metallocarboranes are formal analogues of [π-(arene)Fe, Ru)ⁿ⁺(C₅H₅)] species, and a single crystal X-ray structure of the title compound has established the closo sandwich geometry expected for the molecule on the basis of electron counting rules. The carborane cage was found to be disordered in the crystal but the essential features of the molecular geometry were not obscured. The mesitylene is symmetrically bound to the iron, and the Fe-arene (centroid) distance of 1.60 Å is similar to that found in the previously-characterized [(CH₃)₆C₆]Fe^I(C₅H₅) complex, despite the difference in the metal electronic configurations (d⁶ vs d⁷) and the change from the B₉C₂H₁₁^2? cage to C₅H₅^?. Crystals of 3,1,2-(η⁶-1,3,5-(CH₃)₃C₆H₃)FeC₂B₉H₁₁ are orthorhombic, space group Pn2₁a, with a = 12.638(4), b = 12.432(4), c = 9.686(3) Å.     

Synthesis and crystal structures of the new metal-rich ternary borides Ni12AlB8, Ni12GaB8 and Ni10.6Ga0.4B6—examples for the first B5 zig-zag chain fragment

Single crystals of the new borides Ni₁₂AlB₈, and Ni_10.6Ga_0.4B₆ were synthesized from the elements and characterized by XRD and EDXS measurements. The crystal structures were refined on the basis of single crystal data. Ni₁₂AlB₈ (oC252, Cmce, a=10.527(2), b=14.527(2), c=14.554(2) Å, Z=12, 1350 reflections, 127 parameters, R₁(F)=0.0284, wR₂(F²)=0.0590) represents a new structure type with isolated B atoms and B₅ fragments of a B-B zig-zag chain. Because the pseudotetragonal metric crystals are usually twinned. Ni_10.6Ga_0.4B₆ (oP68, Pnma, a=12.305(2), b=2.9488(6), c=16.914(3) Å, Z=4, 1386 reflections, 86 parameters, R₁(F)=0.0394, wR₂(F²)=0.104) is closely related to binary Ni borides. The structure contains B-B zig-zag chains and isolated B atoms. Ni₁₂GaB₈ is isotypical to the Al-compound (a=10.569(4), b=14.527(4) and c=14.557(5) Å).     

X-ray photoelectron emission studies of mixed selenides AgGaSe2 and Ag9GaSe6

Auger and direct electron specta from crystalline AgGaSe₂ and Ag₉GaSe₆ have been studied with X-ray photoelectron spectroscopy. It is shown that the AgM₅N_4,5N_4,5 and M₄N_4,5N_4,5 Auger spectra are more sensitive to the chemical environment than the Ag 3d direct photoelectron spectra. Furthermore the Auger parameter as defined by Wagner is used in order to characterize the chemical state of these compounds. Last, the XPS spectra of the valence-band region are investigated and chalcogen s and p and noble-metal d bands are clearly identified. The electronic structure of these two selenides does not seem to be determined predominantly by the crystal structure. As a whole, the spectral features are discussed in connection with the character of the chemical bonding and the physical properties of these compounds.     

The crystal structures and magnetic properties of Ba2LaRuO6 and Ca2LaRuO6

Profile analysis of high-resolution, powder neutron-diffraction data was used to refine the previously reported structures of the ordered, distorted perovskites Ba₂LaRuO₆ and Ca₂LaRuO₆. Low-temperature neutron diffraction experiments showed that, at 2K, the former is a Type IIIa antiferromagnet while the latter is Type I. Both compounds have an ordered magnetic moment of $\text{μ}{}_{\mathrm{<mtext>Ru</mtext>}}\text{? 1.95μ}{}_{\mathrm{<mtext>B</mtext>}}$ per Ru⁵⁺ ion. The Néel temperature of Ba₂LaRuO₆ was determined to be 29.5K, and the covalent mixing between the ruthenium and nearest-neighbor anions is described by A²_π = 8.2 ± 1% for Ba₂LaRuO₆ and 8.6 ± 1% for Ca₂LaRuO₆. The ionic radius of a Ru⁵⁺ ion is 0.56 Å. These data are consistently interpreted within the framework of a strongly correlated, half-filled π1 band. Extension of this interpretation to the magnetic data for the perovskites CaRuO₃ and SrRuO₃ leads to a fundamental theoretical prediction.