Structural chemistry and magnetism of dicyclopentadienidehalides of lanthanides Part 8: terbiumdicyclopentadienidebromide [Tb(C5H5)2Br]2

A single-crystal X-ray structural investigation of [Tb(C₅H₅)₂Br]₂ revealed the [Sc(C₅H₅)₂Cl]₂-type structure, space group P2₁/c, with a = 1407.6(2) pm, b = 1644.7(2) pm, c = 1370.6(9) pm, β = 93.46(3)°, V = 3167(2) × 10⁶ pm³, D_c = 2.322 g cm⁻³ and Z = 6 dimers (R = 0.036 for 4627 reflections with I > 3σ(I)). The metal centres have the pseudosymmetry C_2v. Magnetic susceptibility data show Curie-Weiss behaviour between 213 and 6 K with θ_p = −4.5(3) K and a magnetic moment μ = 9.8(1) μ_B close to the Tb³⁺ free-ion value (9.72 μ_B). Below 6 K, deviations from Curie-Weiss behaviour are observed, and at 5.3 K a maximum in the susceptibility is detected which may be caused by intradimer antiferromagnetic spin coupling. The magnetic properties are compared with the prediction of various models, starting from cubic crystal fields and isotropic intramolecular exchange interactions, followed by extension to lower crystal field symmetry (orthorhombic) and anisotropic contributions to the spin coupling. However, a reasonable agreement between the measured and calculated data was not obtained. As in [Gd(C₅H₅)₂Br]₂, the low-temperature behaviour is governed by effects which cannot be described by spin coupling models in the generally accepted form.     

C3H8O3含量对AZ91D镁合金微弧氧化过程及膜层特性的影响

在含有不同C₃H₈O₃含量的硅铝复合电解液中,利用交流脉冲电源在AZ91D镁合金基体上制备了一系列微弧氧化膜。利用SEM和膜层测厚仪分别研究了陶瓷膜层的微观形貌特征及厚度,采用全浸泡实验和电化学阻抗谱测试了膜层在3.5%NaCl中性溶液中的耐蚀性能。结果表明,微弧氧化过程中的起弧电压和终止电压均随C₃H₈O₃含量的增加而呈上升的变化趋势。随着C₃H₈O₃含量的增加,膜层耐蚀性先提高后降低,而膜厚变化幅度不大。膜层的耐蚀性主要取决于内部致密层,当C₃H₈O₃含量为5 mL/L时,膜层相对较致密,因而表现出良好的耐蚀性能。     

High resolution NMR and structural investigations of the 2-ammonium 2-methyl propanol dihydrogenodiphosphate [(CH3)2C(NH3)CH2OH]2H2P2O7

We report on high resolution ¹³C and ³¹P NMR and X-ray diffraction measurements of the organic dihydrogenodiphosphate (C₄H₁₂NO)₂H₂P₂O₇. The obtained ¹³C magic angle spinning (MAS) NMR spectrum at room temperature shows four resonances at 22, 23, 57 and 66 ppm which we attribute to the four magnetically inequivalent carbons of the organic cation, the two CH₃, the CH₂ and the quaternary carbon, respectively. The corresponding ³¹P MAS NMR spectrum presents two isotropic resonances at − 9.2 and − 6.9 ppm assigned to the two crystallographically inequivalent sites of the phosphorus atoms in the structure. The obtained NMR results are in quite good agreement with our X-ray data on the same sample. These results confirm the non-centrosymmetric structure of this material and its ability to exhibit non-linear optical properties.     

Spectroscopy, magnetism and non-radiative processes in heteronuclear Cu:Pr squarate; [Pr2Cu(C4O4)4(H2O)16]·2H2O

In the present work, the spectroscopic and magnetic properties of heteronuclear Cu:Pr squarate are reported. Single crystals of [Pr₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O were obtained by reaction of squaric acid, praseodymium chloride and copper chloride in water solution according to the procedure described earlier. The crystals of title compound are isomorphic with [La₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O crystal, where squarate anions participate as bridging ligands between metal ions.

The UV region of absorption spectra of the title compound is dominated by C–T band of Cu(II), f–d transition of Pr(III) and internal π–π*(A_1g→E_u) and π–π*(A_1g→E_g) ligand transitions. In visible and IR regions, t_2g–e_g of copper Cu(II) as well as ³H₄→³P_J, ¹D₂, ¹G₄, ³F_J, ³H₆ Pr(III) transitions at 293 and 4 K were recorded. At low temperature splitting given by Jahn–Teller effect can be observed. Significant anisotropy of d–d transitions intensities confirms well the Jahn–Teller effect, too. Unexpectedly high intensity of ³H₄→¹G₄ transition is probably due to the intensity borrowing from the Cu (II) d–d transition.

The ³P₀ and ¹D₂ emission of Pr(III) in the [Pr₂Cu(C₄O₄)₄(H₂O)₁₆]·2H₂O crystals is quenched even at 77 K. Whereas emission of appropriate polynuclear europium squarate was detected. The pathways of excited state quenching by e_g levels of Cu(II), multhiphonon relaxation and concentration quenching can be considered in the system under studies. Magnetic susceptibility measurements were carried out in 300–1.7 K temperature range and are discussed in relation to the structure.

Effect of the polymeric structure on spectroscopic behaviour is presented. Selectivity of polymeric europium squarate in vitro test for different tumor cells is shown.     

Fermi surface studies of the pressure induced organic superconductor (ET)3Cl2.2H2O

The effects of temperature, pressure and magnetic field on the electrical transport of single crystal of (ET)₃Cl₂.2H₂O are reported. Increasing pressure gradually reduces the ordering temperature of a charge density wave ground state from 160 K at 1 bar to 6 K at 10.2 kbar. A superconducting state with T_c > 4 K is stabilised between 10.2 kbar and 13.5 kbar. Above 12.5 kbar, the observation of Shubnikov-de Haas oscillations allows the pressure dependences of the area of a closed Fermi surface pocket and the associated carrier effective mass to be deduced.     

Temperature dependence of infrared spectra of (ET)4Hg3I8 crystals; H8- and D8-ET derivatives

Infrared spectra of H₈-(ET)₄Hg₃I₈ and analogous salt with deuterated ET molecule D₈-(ET)₄Hg₃I₈ are studied. Polarized reflectance spectra from single crystals and absorption spectra of powders are measured as a function of temperature. The influence of semiconductor-semiconductor phase transitions on IR spectra is considered. It is observed that the ν₂₇(b_lu) mode of ET molecule couples with electrons.     

Magnetocrystalline anisotropy of R2Fe17Hx (x=0, 3) single crystals

The magnetocrystalline anisotropy of R₂Fe₁₇ (R=Y, Gd, Tb, Ho and Er) and their hydrides are studied by analyzing the magnetization curves of single crystal samples in the temperature range 4.2–300 K in magnetic fields up to 140 kOe. There is no noticeable influence of hydrogenation on the magnetic anisotropy in the Y₂Fe₁₇ and Gd₂Fe₁₇ compounds. An easy-plane to easy-cone transition is detected for a Tb₂Fe₁₇H₃ single crystal after hydrogenation. A significant change of the magnetization process has been observed in the hydrides Ho₂Fe₁₇H₃ and Er₂Fe₁₇H₃. Hydrogenation induces a FOMP-type transition in the Ho₂Fe₁₇H₃ compound and, on the contrary, leads to the disappearance of the FOMP type transition in the Er₂Fe₁₇H₃ compound. The obtained results are discussed on the basis of a model based on the interaction of the quadrupolar moment and the magnetic moment of the 4f electron shell of the rare earth ion with the interstitial hydrogen. It is established that the orientation of the quadrupolar moment of the asymmetric 4f shell with respect to the direction of the resulting magnetic moment of 4f electrons plays an important role.     

Phase transition of γ-(BEDT-TTF)3(HSO4)2

The structural properties and the metal-insulator (MI) transition of γ-ET₃(HSO₄)₂ (1) are discussed, in comparison with those of γET₃(ClO₄)₂ (2). Transition of 1 is related to a structural change, as in the case of 2. The substitution of hydrogen of the anion with deuterium lengthens the O O distance of intermolecular hydrogen bonds between the two anions, although an MI transition temperature is not changed appreciably. The hydrogen bonds between the two anions make the rotation of the anion molecules strongly hindered and shift their positions close to each other, which enables the puckering motion of the ethylene bridge of ET molecules easily.     

Simulation of the crystal field effect on the Pr ion in K2La1−xPrxCl5 ternary chlorides

The high resolution absorption, luminescence and excitation spectra of the orthorhombic potassium lanthanum praseodymium ternary chloride, K₂La_1−xPr_xCl₅, (0.02 ≤ x ≤ 0.15) single crystals were recorded at 4, 77 and 293 K with different excitation sources. The experimental 4f² energy level scheme of the Pr³⁺ ion in K₂LaCl₅ derived from the absorption and emission spectra consisted of 86 (out of 91) Stark components. This energy level scheme was simulated by using a phenomenological crystal field (cf) model which included eight free ion and nine cf parameters according to the C_2v symmetry. Despite the approximate C_2v point symmetry instead of the real C_s one, the simulation yielded a very satisfactory rms deviation of 17 cm⁻¹ between the experimental and calculated energy level schemes. The results, especially the weak cf strength, are discussed taking into account the bonding characteristics in K₂LaCl₅.     

Hydrogen absorption properties of the slurry system composed of liquid C6H6 and F-treated Mg2Ni

The hydrogenation characteristics of the slurry composed of the NH₄F solution treated Mg₂Ni and liquid C₆H₆ were studied. The F-treatment results in a net-shaped MgF₂ surface and higher nickel content in the sub-layer. It is found that the hydride of the NH₄F treated alloy has a much higher activity for the hydrogenation of benzene. The catalytic activity for hydrogenation of the alloy depended strongly on the surface properties of the catalyst. At 483 K and under a hydrogen pressure of 4.0 MPa, the alloy absorbed hydrogen first, transformed into hydride and then the benzene was hydrogenated to cyclohexane with the hydride as the catalyst. The hydrogen absorption capacity of slurry system composed of 20 wt.% treated alloy and benzene reached 6.4 wt.% and the hydrogenation completed in 20 min. Results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis on the crystal structure, surface composition and surface morphology of the untreated and treated alloy are presented and discussed.     

Ca15(CBN)6(C2)2O- a new cubic structure type containing CBN-anions together with acetylide and oxo anions

Ca₁₅(CBN)₆(C₂)₂O contains CBN⁴⁻ anions as well as C₂⁻ units and isolated O²⁻ anions. The compound is obtained by heating a stoichiometric mixture of CaO, C and BN with an excess of Ca in sealed niobium ampoules to 1270 K. It crystallizes in the space group Ia d with a = 1656.84(9) pm. Preparation, crystal structure, NMR and IR-spectroscopic properties are discussed.     

Optical study of praseodymium dicarboxylate [Pr(H2O)]2[O2C(CH2)3CO2]3.4H2O

Praseodymium dicarboxylate, [Pr(H₂O)]₂[O₂C(CH₂)₃CO₂]₃.4H₂O]–glutarate, Pr[glut], is synthesized by hydrothermal techniques. The title compound crystallizes in the monoclinic space group C2/c (No. 15). The rare earth cation is coordinated by nine oxygen atoms, eight oxygen atoms from the carboxylate groups and one from the water molecule. The local symmetry of Pr site is low, C_s. The absorption spectra of Pr[glut] are recorded from the visible to the far IR domain at 300, 77 and 9 K. Under various Ar⁺ laser excitations no emission is detected from ³P₀ and ¹D₂ excited levels of Pr³⁺ ion. In the low temperature absorption spectra only one electronic line is recorded for ³H₄→³P₀ transition. It confirms a unique local environment for the rare earth ion in Pr[glut]. The utility of the ‘barycenter curves’ in the attribution of electronic lines is demonstrated. Energy level scheme of 36 Stark components is deduced from the absorption spectra. The parametric calculation was performed on the whole 4f² (Pr³⁺) configuration with the starting set of crystal field parameters obtained previously for the Eu³⁺ ion in the isostructural compound. Eight free ion and nine phenomenological crystal field parameters in C_2v symmetry reproduce quite well several electronic levels of Pr³⁺ ion experimentally observed in Pr[glut]. A good r.m.s. standard deviation of 14.8 cm⁻¹ is obtained.     

Dielectric relaxation and ionic conductivity studies of [N(CH3)4]2Cu0.5Zn0.5Cl4

WO₃-doped zinc titanate ceramics were prepared by conventional mixed-oxide method combined with a chemical processing. The effects of WO₃ additions on the phase structure and phase transitions of zinc titanate ceramics were investigated by high-temperature X-ray diffractometry (HTXRD) and transmission electron microscopy (TEM). The results showed that the major phase of zinc titanate ceramics transformed from zinc orthotitanate phase to zinc metatitanate phase with the amounts of WO₃ additions increasing. Small WO₃ (<1.00 mass%) addition accelerated the transition of ZnTiO₃ to Zn₂TiO₄, while excessive WO₃ addition restrained the transition. HTXRD showed that WO₃ enhanced the stability of Zn₂Ti₃O₈ and weakened the stability of ZnTiO₃. A precipitate within the Zn₂TiO₄ matrix was observed. Viewed along the orientation of Zn₂TiO₄, the precipitate was found to have a rectangular shape and to be nanometer level in size; its composition was concluded to be Zn₂Ti₃O₈. The dielectric properties of WO₃-doped zinc titanate ceramics were measured at different frequencies. The results showed the decreasing tendency with the increasing measuring frequencies for both the dielectric constants and the loss tangents, and there existed maximum values when the amount of WO₃ was 0.50 mass%.     

Thermal expansion studies on Th(MoO4)2, Na2Th(MoO4)3 and Na4Th(MoO4)4

Thermal expansion behavior of Th(MoO₄)₂, Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ was studied under vacuum in the temperature range of 298–1123 K by high temperature X-ray diffractometer. Th(MoO₄)₂ was synthesized by reacting ThO₂ with 2 mol of MoO₃, at 1073 K in air and Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were prepared by reacting Th(MoO₄)₂ with 1 and 2 mol of Na₂MoO₄, respectively at 873 K in air. The XRD data of Th(MoO₄)₂ was indexed on orthorhombic system where as XRD data of Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were indexed on tetragonal system. The lattice parameters and cell volume of all the three compounds, fit into polynomial expression with respect to temperature, showed positive thermal expansion (PTE) up to 1123 K. The average value of thermal expansion coefficients for Th(MoO₄)₂, Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were determined from the high temperature data.     

Novel BEDT-TTF salts with magnetic anions [MoOCl4(H2O)] and [Re2(NCS)10]

We report two novel BEDT-TTF salts containing magnetic transition metal anions. Both compounds are unusual in not containing discrete layers of anions and cations. In (BEDT-TTF)[MoOCl₄(H₂O)] the anions form hydrogen-bonded chains that lie in between 1-dimensional ribbons of edge-linked BEDT-TTF molecules. The compound is semiconducting with σ₃00K 0.5Scm^{− 1} E_A0.leV. In (BEDT-TTF)₃[Re₂(NCS)₁₀] CH₂Cl₂ no continuous network of BEDT-TTF exists, however π-π interactions are seen between the cation and the [Re₂(NCS)₁₀]^{3 −} anion. The compound is semiconducting with σ300K 0.01Scm⁻¹; E_A = 0.30eV.     

Structural and thermal studies on Na2U(MoO4)3 and Na4U(MoO4)4

In Na–U(IV)–Mo–O system, two quaternary compounds Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ were prepared by solid state reactions of Na₂MoO₄, UMoO₅ and MoO₃ in the required stoichiometric ratio at 500 °C in evacuated sealed quartz ampoules. The crystal structure of both the compounds were derived from X-ray powder diffraction data in the tetragonal system by Rietveld profile method. Na₂U(MoO₄)₃ has scheelite structure, whereas Na₄U(MoO₄)₄ has scheelite superlattice structure.

TG curves of Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ did not show any significant weight change up to 750 °C in an inert atmosphere. During the heating cycle in an inert atmosphere, DTA curves of Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ showed endothermic peaks due to the melting of the compounds at 740 °C and 730 °C, respectively. Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄, when heated in air atmosphere at 1200 °C, decomposed to form Na₂U₂O₇ which was confirmed by weight loss calculation and XRD.     

Mg6Ir2H11, a new metal hydride containing saddle-like [IrH4] and square-pyramidal [IrH5] hydrido complexes

Mg₆Ir₂H₁₁ has been synthesised by both hydrogenation of the intermetallic compound Mg₃Ir at 20 bar and 300 °C, and sintering of the elements at 500 °C under 50 bar hydrogen pressure. Neutron powder diffraction on the deuteride indicates a monoclinic structure (space group P2₁/c, Mg₆Ir₂D₁₁: a=10.226(1), b=19.234(2), c=8.3345(9) Å, β=91.00(1)°, T=20 °C) that is closely related to orthorhombic Mg₆Co₂H₁₁. It contains a square-pyramidal [IrH₅]⁴⁻ complex and three saddle-like [IrH₄]⁵⁻ complexes of which one is ordered and two are disordered. Five hydride anions H⁻ are exclusively bonded to magnesium. The compound has a red colour, is presumably non-metallic and decomposes under 3 bar argon at 500 °C into Mg₃Ir, iridium and a previously unreported intermetallic compound of composition Mg₅Ir₂.     

Crystal structures and structural relationships of KFe2(SeO2OH)(SeO3)3 and SrCo2(SeO2OH)2(SeO3)2

The new phases KFe₂(SeO₂OH)(SeO₃)₃ and SrCo₂(SeO₂OH)₂(SeO₃)₂ have been synthesized under low-hydrothermal conditions and their structures were determined by single-crystal X-ray methods. Both compounds are monoclinic; KFe₂(SeO₂OH)(SeO₃)₃: space group P2, A = 9.983(4), B = 5.270(1), C = 10.614(4) Å, β = 97.42(2)°, V = 553.7 ų, Z = 2; SrCo₂(SeO₂OH)₂(SeO₃)₂: space group P2ln, A = 14.984(2), B = 5.286(1), C = 13.790(2) Å, β = 94.72(1)°, V = 1088.5 ų , Z = 4. The refinements converged to R-values of 2.9 and 3.6% respectively.

The atomic arrangement in KFe₂(SeO₂OH)(SeO₃)₃ and SrCo₂(SeO₂OH)₂(SeO₃)₂ is based on isolated MO₆ octahedra (M = Fe³⁺, Co²⁺), which are corner-linked via trigonal pyramidal selenite groups to a framework structure. Interstitials are occupied by potassium or strontium atoms in ten- or eight-coordination respectively, and by the lone-pair electrons of the Se⁴⁺ atoms. Both compounds are not isotypic but are closely related and may be interpreted as different distortions of an idealized structure type in space group P2/m, which was modelled for a theoretical compound SrFe₂(SeO₃)₄ by distance least squares refinement (program ).     

Crystal field analysis of EuCl3.6H2O

Absorption and magnetic circular dichroism (MCD) spectra of polycrystalline EuCl₃.6H₂O samples were recorded between 16 000 and 36 000 cm⁻¹ at ambient temperature and at 77 K. A total of 104 crystal field transitions has been observed in the spectra. The MCD spectrum resembles the first derivative of the absorption spectrum, indicating the presence of (pseudo) A-terms. The advantage of MCD is the possibility of detecting quasi-degenerate crystal field levels, which are not resolved in the absorption spectrum. The coordination polyhedron around Eu³⁺ is a distorted square antiprism (C.N.=8). In order to make the crystal field calculations more tractable, the real C₂ symmetry of the europium site is approximated by a C_2v symmetry. The energy levels of the 4f⁶ configuration of Eu³⁺ are parametrized in terms of 20 free ion parameters and 9 B_q^k crystal field parameters. J-mixing is taken into account.     

Effect of various carbides on the dissolution behavior of Ti(C0.7N0.3) in a Ti(C0.7N0.3)–30Ni system

HfC, TaC, or WC were individually added to a Ti(C_0.7N_0.3)–30 wt% Ni system, in order to investigate microstructural changes and the dissolution behaviors of Ti(C_0.7N_0.3) and the carbides. Of these systems, the Ti(C_0.7N_0.3)–WC–Ni system proved to be the most favorable for the refinement of microstructure. The fraction for the cross-sectional area of the Ti(C_0.7N_0.3) cores, which is related to the amount of Ti(C_0.7N_0.3) dissolved, increases and the thickness of solid solution rims decreases in the order of HfC, TaC, and WC added. This finding indicates that the dissolution rate of Ti(C_0.7N_0.3) in a Ni melt is the lowest when WC is added. In addition, it was found that the average dissolution rate of Ti(C_0.7N_0.3) in the HfC-containing system is 1.6 and 1.9 times higher than those for Ti(C_0.7N_0.3) in the TaC- and WC-containing systems at the same sintering conditions. Further, the dissolution rates of TaC and WC were 80% of the rate found for HfC during the formation of the outer rim.