Nuclear magnetic resonance studies of methyl-5, 6-dicarboxy-2-norbornene derivatives

A simple procedure is provided for the quantitative analysis of Diels-Alder adduct prepared from commercial methylcyclopentadiene and maleic anhydride by NMR spectra without further separation of its components. The adduct is considered as a mixture of endo norbornene derivatives (C_n), (D_n), (E) and (F_n) which are obtained from 1-, 2- and 5-methylcyclopentadiene and cyclopentadiene, respectively. The quantitative analysis of the adduct can be made on a basis of the ratio of the signal intensities of the olefinic protons in the adduct. The result shows that the adduct prepared under mild conditions mainly consists of three norbornene derivatives (C_n), (D_n) and (F_n), with a negligibly small amount of (E). When the adduct prepared under mild conditions is heated, it contains the exo isomers (Cx), (Dx) and (Fx). The ratio of the endo and the exo norbornene derivatives, i.e. ((C_n) + (D_n) + (F_n)):((C_x) + (D_x) + (F_x)), may be estimated from the signal intensities of the 5- and 6-protons. As the result of the analyses of the adducts which are obtained by heating at different temperatures the adduct prepared under mild conditions, the mole fraction of 2-methyl isomers (D_n) and (D_x), which is found to be 58 % in the adduct prepared at ? 15°C, keeps on increasing with rising temperature and shows almost the same value, ～86%, when heated above 150°C. Therefore, the equilibrium between 1-methyl and 2-methyl isomers does not change above 150°C. On the other hand, the isomerization from endo to exo isomers is not found below 110°C, and then exo isomers keep on increasing above 140°C.     

The electronic structure of FeO 4 2− , RuO4, RuO 4 − , RuO 4 2− and OsO4 by the HFS-DVM method

The electronic structures of FeO ₄ ^2? , RuO₄, RuO ₄ ^? , RuO ₄ ^2? and OsO₄ have been investigated using the Hartree-Fock-Slater Discrete Variational Method. The calculated ordering of the valence orbitals is 2t ₂, 1e, 2a ₁, 3t ₂ andt ₁ with thet ₁ orbital as the highest occupied. The first five charge transfer bands are assigned as:t ₁→2e(v ₁), 3t ₂→2e(v ₂),t ₁→4t ₂(v ₃), 3t ₂→4t ₂(v ₄) and 2a ₁→4t ₂(v ₅). It is suggested that ad-d transition should be observed at 1.5 eV in RuO ₄ ^? and RuO ₄ ^2? .     

Gas-phase solvation of protonated aliphatic amines: methyl,ethyl, n-propyl,and iso-propylamine

The thermodynamic quantities K_{n?1 n}, ΔG⁰_{n?1, n} and ΔS⁰_n?1, n for the gas phase equilibrium reactions RNH⁺₃(RNH₂)_n?1 + RNH₂ = RNH⁺₃(RNH₂)_n, where n ? 3 and R indicates an alkyl group (CH₃, C₂H₅, n-C₃H₇ and iso-C₃H₇), have been determined.     

Characterization of quasi-one-dimensional S=1/2 Heisenberg antiferromagnets Sr2Cu(PO4)2 and Ba2Cu(PO4)2 with magnetic susceptibility, specific heat, and thermal analysis

Properties of Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ having [Cu(PO₄)₂]_∞ linear chains in their structures with Cu-O-P-O-Cu linkages were studied by magnetic susceptibility (T=2-400 K, H=100 Oe) and specific heat measurements (T=0.45-21 K). Magnetic susceptibility versus temperature curves, χ(T), showed broad maxima at T_M=92 K for Sr₂Cu(PO₄)₂ and T_M=82 K for Ba₂Cu(PO₄)₂ characteristic of quasi-one-dimensional systems. The χ(T) data were excellently fitted by the spin susceptibility curve for the uniform S=1/2 chain (plus temperature-independent and Curie-Weiss terms) with g=2.153(4) and J/k_B=143.6(2) K for Sr₂Cu(PO₄)₂ and g=2.073(4) and J/k_B=132.16(9) K for Ba₂Cu(PO₄)₂ (Hamiltonian H=JΣS_iS_i+1). The similar J/k_B values were obtained from the specific heat data. No anomaly was observed on the specific heat from 0.45 to 21 K for both compounds indicating that the temperatures of long-range magnetic ordering, T_N, were below 0.45 K. Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ are an excellent physical realization of the S=1/2 linear chain Heisenberg antiferromagnet with k_BT_N/J<0.34% together with Sr₂CuO₃ (k_BT_N/J≈0.25%) and γ-LiV₂O₅ (k_BT_N/J<0.16%). Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ were stable in air up to 1280 and 1150 K, respectively.     

Determination of K shell X-ray intensity ratios for some heavy elements

The K shell X-ray intensity ratios K_α2/K_α1, K_β1,3/K_α1 and K_β2/K_α1 for 21 elements with 65⩽Z⩽92 have been measured using an incident photon energy of 123.6 keV. The X-rays have been measured with a Si(Li) semiconductor detector. K_β and K_α X-rays have been analyzed into the components K_β1,3 and K_β2 and K_α1 and K_α2, respectively, using a computer program. The experimental results were compared with the theoretical values of Scofield and available experimental results. All X-ray intensity ratios values have been plotted versus atomic number.     

Excess molar quantities of (a halogenated n-alkane + an n-alkane) A comparative study of mixtures containing either 1-chlorobutane or 1,4-dichlorobutane

Excess molar volumes V_m^E at 298.15 K were obtained, as a function of mole fraction x, for series I: {x1-C₄H₉Cl + (1 ? x)n-C_lH_{2l + 2}}, and II: {x1,4-C₄H₈Cl₂ + (1 ? x)n-C_lH_{2l + 2}}, for l = 7, 10, and 14. 10, and 14. The instrument used was a vibrating-tube densimeter. For the same mixtures at the same temperature, a Picker flow calorimeter was used to measure excess molar heat capacities C_{p, m}^E at constant pressure. V_m^E is positive for all mixtures in series I: at x = 0.5, V_m^E/(cm³ · mol^?1) is 0.277 for l = 7, 0.388 for l = 10, and 0.411 for l = 14. For series II, V_m^E of {x1,4-C₄H₈Cl₂ + (1 ? x)n-C₇H₁₆} is small and S-shaped, the maximum being situated at x_max = 0.178 with V_m^E(x_max)/(cm³ · mvl^?1) = 0.095, and the minimum is at x_min = 0.772 with V_m^E(x_min)/(cm³ · mol^?1) = ?0.087. The excess volumes of the other mixtures are all positive and fairly large: at x = 0.5, V_m^E/(cm³ · mol^?1) is 0.458 for l = 10, and 0.771 for l = 14. The C_{p, m}^Es of series I are all negative and |C_{p, m}^E| increases with increasing l: at x = 0.5, C_{p, m}^E/(J · K^?1 · mol^?1) is ?0.56 for l = 7, ?1.39 for l = 10, and ?3.12 for l = 14. Two minima are observed for C_{p, m}^E of {x1,4-C₄H₈Cl₂ + (1 ? x)n-C₇H₁₆}. The more prominent minimum is situated at x′_min = 0.184 with C_{p, m}^E(x′_min)/(J · K^?1 · mol^?1) = ?0.62, and the less prominent at x″_min = 0.703 with C_{p, m}^E(x″_min)/(J · K^?1 · mol^?1) = ?0.29. Each of the remaining two mixtures (l = 10 and 14) has a pronounced minimum at low mole fraction (x_min = 0.222 and 0.312, respectively) and a broad shoulder around x = 0.7.     

Exchange interactions in R2Fe17−xGax (R=Y, Sm, Gd, Tb, Ho and Tm) compounds

We calculated the molecular field coefficients, n_FeFe and n_RFe (R=Sm, Gd, Tb, Ho and Tm), for R₂Fe_17−xGa_x and the values of n_FeFe and n_SmFe for R₂Fe_17−xT_x (T=Al and Si) using the experimental values of the Curie temperature. The values of n_FeFe increase in spite of the decrease of μ_Fe for 0?x?5. The values of n_SmFe have large values when the magnetic anisotropy is axial. For 6?x?8, the values of n_FeFe, n_HoFe and n_TmFe increase largely, which is related to the change of the easy magnetization direction. For Y₂Fe_17−xT_x (T=Ga and Al), the values of n_FeFe have a maximum value with increasing those of μ_Fe. With increasing V⁻¹, the values of n_FeFe have a maximum value around the same value of V⁻¹ for Y₂Fe_17−xT_x (T=Ga and Al). For Y₂Fe_17−xSi_x, the values of n_FeFe increase with increasing V⁻¹.     

Excess molar volumes of (cyclohexanone+trichloromethane,or 1,2-dichloroethane,or trichloroethene,or 1,1,1-trichloroethane,or cyclohexane) at T=308.15 K,and of (cyclohexanone+dichloromethane) at T=303.15 K

Excess molar volumes V_m^E have been measured using a dilatometric technique for mixtures of cyclohexanone (C₆H₁₀O) with trichloromethane (CHCl₃), 1,2-dichloroethane (CH₂ClCH₂Cl), trichloroethene (CHClCCl₂), 1,1,1-trichloroethane (CCl₃CH₃), and cyclohexane (c-C₆H₁₂) at T=308.15 K, and for cyclohexanone+dichloromethane (CH₂Cl₂) at T=303.15 K. Throughout the entire range of the mole fraction χ of C₆H₁₀O, V_m^E has been found to be positive for χ C₆H₁₀O+(1−χ)c-C₆H₁₂, and negative for χ C₆H₁₀O+(1−χ)CH₂Cl₂, χ C₆H₁₀O+(1−χ)CHClCCl₂, χ C₆H₁₀O+(1−χ)CHCl₃, and χ C₆H₁₀O+(1−χ) CCl₃CH₃. For χ C₆H₁₀O+(1−χ)CH₂ClCH₂Cl, V_m^E has been found to be positive at lower values of χ and negative at high values of χ, with inversion of sign from positive to negative values of V_m^E for this system occurring at χ∼0.78. Values of V_m^E for the various systems have been fitted by the method of least squares with smoothing equation, and have been discussed from the viewpoint of the existence specific interactions between the components.     

A systematic study of magnetic order in divalent europium perovskites

The magnetic properties of a series of cubic perovskite materials, Eu(Al_0.5Ta_0.5)O₃, Eu(Mg_0.5W_0.5)O₃, and Eu(Lu_0.5Ta_0.5)O₃ have been investigated using bulk magnetic and Mössbauer techniques. Eu(Al_0.5Ta_0.5)O₃ is a ferromagnet (T_c ～ 5°K, θ_c = + 8°K), Eu(Lu_0.5Ta_0.5)O₃ is an antiferromagnet (T_N = 4.0, θ_c = ?8°K), while Eu(Mg_0.5W_0.5)O₃ is probably antiferromagnetic (T_N = 2.8°K, θ_c = ? 1°K). These data are compared with the known properties of EuLiH₃ and EuTiO₃ and a sharp drop in θ_c as a function of increasing lattice constant is noted. A molecular field theory analysis of the data yields two possible sets of nn (J₁) and nnn (J₂) exchange constants for each compound which are compared with existing theories.     

Oxygen nonstoichiometry and chemical stability of Nd2−xSrxNiO4+δ

Nonstoichiometric variation of oxygen content in Nd_2−xSr_xNiO_4+δ (x=0, 0.2, 0.4) and decomposition P(O₂) were determined by means of high temperature gravimetry and coulometric titration. The measurements were carried out in the temperature range from 873 to 1173 K and the P(O₂) range from 10⁻²⁰ to 1 bar. Nd_2−xSr_xNiO_4+δ shows the oxygen excess and the oxygen deficient composition depending on P(O₂), temperature, and the Sr content. To evaluate the characteristics of oxygen nonstoichiometric behavior, partial molar enthalpy of oxygen was calculated. The value of partial molar enthalpy of oxygen slightly approaches zero as δ increases in the oxygen excess region while that is independent of δ in the oxygen deficient region. Discussion was made by comparing data of this study with nonstoichiometric and thermodynamic data of La_2−xSr_xNiO_4+δ: Nd_2−xSr_xNiO_4+δ show more oxygen excess than La_2−xSr_xNiO_4+δ in the higher P(O₂) region, while the nonstoichiometric behavior in the oxygen deficient composition is almost the same. The variation of partial molar enthalpy of oxygen with δ for Nd_2−xSr_xNiO_4+δ in the oxygen excess region is much smaller than that of La_2−xSr_xNiO_4+δ. The oxygen nonstoichiometric behavior of Nd_2−xSr_xNiO_4+δ is more ideal-solution-like than that of La_2−xSr_xNiO_4+δ.     

Subsolidus phase relations and crystal structures of R-Ca-Cu-O (R=Nd, Sm, Gd, Tm) systems

The subsolidus phase relations of R₂O₃-CaO-CuO ternary systems (R=Nd, Sm, Gd, Tm) have been investigated by X-ray powder diffraction. All samples were synthesized at about 950° in air. There exists a ternary compound Ca_14−xR_xCu₂₄O₄₁ (x = 4 for R=Nd, Gd and x = 5 for R = Sm) and a ternary solid solution Ca_2+xR_2−xCu₅O₁₀ (R=Nd, Sm, Gd, Tm) with a wide composition range Δx of about 0.6. The compound Ca_14−xR_xCu₂₄O₄₁ possesses a layered orthorhombic structure and is isostructural to Sr_14−xCa_xCu₂₄O₄₁. The lattice parameters a and c of the compound are basically independent of the ionic radius of R, while the lattice parameter b and unit-cell volume V decrease substantially with the decrease of the ionic radii of R. The Ca_2+xR_2−xCu₅O₁₀ solid solution is isostructural to Ca_2+xY_2−xCu₅O₁₀, the structure of which is based on an orthorhombic “NaCuO₂-type” subcell containing infinite one-dimensional chains of edge-shared square planar cuprate groups crosslinked by the layered cations Ca and R that locate in the inter-chain tunnels.     

Relationship between interlayer hydration and photocatalytic water splitting of A′1−xNaxCa2Ta3O10·nH2O (A′=K and Li)

Partial replacement of alkaline metals in anhydrous KCa₂Ta₃O₁₀ and LiCa₂Ta₃O₁₀ was studied to control interlayer hydration and photocatalytic activity for water splitting under UV irradiation. A′_1−xNa_xCa₂Ta₃O₁₀·nH₂O (A′=K and Li) samples were synthesized by ion exchange of CsCa₂Ta₃O₁₀ in mixed molten nitrates at 400 °C. In K_1−xNa_xCa₂Ta₃O₁₀·nH₂O, two phases with the orthorhombic (C222) and tetragonal (I4/mmm) structures were formed at x?0.7 and x?0.5, respectively. Upon replacement by Na⁺ having a larger enthalpy of hydration (ΔH_h⁰), the interlayer hydration occurred at x?0.3 and the hydration number (n) was increased monotonically with an increase of x. Li_1−xNa_xCa₂Ta₃O₁₀·nH₂O showed a similar hydration behavior, but the phase was changed from I4/mmm (x<0.5, n∼0) via P4/mmm (x∼0.5, n∼1) to I4/mmm (x∼1.0, n∼2). The photocatalytic activities of these systems after loading 0.5 wt% Ni were quite different each other. K_1−xNa_xCa₂Ta₃O₁₀·nH₂O exhibited the activity increasing in consistent with n, whereas Li_1−xNa_xCa₂Ta₃O₁₀·nH₂O exhibited the activity maximum at x=0.77, where the rates of H₂/O₂ evolution were nearly doubled compared with those for end-member compositions (x=0 and 1).     

The role of boron trichloride in the synthesis of phenyltrichlorosilane from benzene and trichlorosilane

Benzene and trichlorosilane form phenyltrichlorosilane and hydrogen. Boron trichloride has long been used as the preferred catalyst for this process. The mechanism of catalysis is indicated as follows: BCl₃ + xHSiCl₃ → H_xBCl_3?x + xSiCl₄; H_xBCl_3?x + xC₆H₆ → (C₆H₅)_x + xH₂; (C₆H₅)_xBCl_3?x + xHSiCl₃ → H_xBCl_3?x + xC₆H₅SiCl₃.     

Influence of Oxygen Nonstoichiometry on the Spectral Properties of Solid Solutions LaNb2−2xTa2xVO9−δ (x=0-0.4) and LaTa2−2xNb2xVO9−δ (x=0-0.1)

Phase equilibria in the LaVO₄-Nb₂O₅-Ta₂O₅ system were analyzed. New solid solutions LaTa_2−2xNb_2xVO_9−δ (x=0-0.1) and LaNb_2−2xTa_2xVO_9−δ (x=0-0.4) were detected in this system. The structures of the vanadate-niobate LaNb₂VO₉ and vanadate-tantalate LaTa₂VO₉ are not known. The structures of the vanadate-tantalate LaTa₂VO₉ and LaTa₂VO₉-based solid solutions are similar to the structure of LaTa₇O₁₉, which refers to the hexagonal crystal system. The influence of the oxygen nonstoichiometry δ(x) on crystallochemical characteristics and spectral properties of these solid solutions were examined by the X-ray phase analysis, IR and radio spectroscopic methods. A correlation between the nonstoichiometry δ(x) and the volume of a unit cell V(x) of solid solutions LaTa_2−2xNb_2xVO_9−δ was found. The IR spectrum of LaTa₂VO_9−δ transformed in going from δ=0 to δ≠0. Two types of VO₄ tetrahedra were formed in solid solutions LaNb_2−2xTa_2xVO_9−δ depending on δ(x).     

Synthesis and crystal structure of Ln2MGe4O12, Ln=rare-earth element or Y; M=Ca, Mn, Zn

The crystal structure of the promising optical materials Ln₂M²⁺Ge₄O₁₂, where Ln=rare-earth element or Y; M=Ca, Mn, Zn and their solid solutions has been studied in detail. The tendency of rare-earth elements to occupy six- or eight-coordinated sites upon iso- and heterovalent substitution has been studied for the Y_2−xEr_xCaGe₄O₁₂ (x=0-2), Y_2−2xCe_xCa_1+xGe₄O₁₂ (x=0-1), Y₂Ca_1−xMn_xGe₄O₁₂ (x=0-1) and Y_2−xPr_xMnGe₄O₁₂ (x=0-0.5) solid solutions. A complex heterovalent state of Eu and Mn in Eu₂MnGe₄O₁₂ has been found.     

Charge compensation and oxidation in NaxCoO2−δ and LixCoO2−δ studied by XANES

A comparative study on the oxidation and charge compensation in the A_xCoO_2−δ systems, A=Na (x=0.75, 0.47, 0.36, 0.12) and Li (x=1, 0.49, 0.05), using X-ray absorption spectroscopy at O 1s and Co 2p edges is reported. Both the O 1s and Co 2p XANES results show that upon removal of alkali metal from A_xCoO_2−δ the valence of cobalt increases more in Li_xCoO_2−δ than in Na_xCoO_2−δ. In addition, the data of O 1s XANES indicate that charge compensation by oxygen is more pronounced in Na_xCoO_2−δ than in Li_xCoO_2−δ.     

Synthesis and crystal structure of three silver indium double phosphates

Three new silver indium double phosphates Ag₃In(PO₄)₂ (I), β-(II) and α-Ag₃In₂(PO₄)₃ (III) were synthesized by solid state method (I and II—700 °C, III—900 °C). Compounds I and II crystallize into a monoclinic system (I—sp. gr. C2/m, Z=2, a=8.7037(1)Å, b=5.4884(1)Å, c=7.3404(1)Å, β=93.897(1)°; II—sp. gr. C2/c, Z=4, a=12.6305(1)Å, b=12.8549(1)Å, c=6.5989(1)Å, β=113.842(1)°), and compound III crystallize into a hexagonal system (sp. gr. R-3c, Z=6, a=8.9943(1)Å, c=22.7134(1)Å). Their crystal structures were determined by the Rietveld analysis (I—R_p=6.47, R_wp=8.54; II—R_p=5.67, R_wp=6.40; III—R_p=7.30, R_wp=9.91). Structure of Ag₃In(PO₄)₂ is related to the sodium chromate structure type and is isotypic to α-Na₃In(PO₄)₂. The polymorphous modifications of β- and α-Ag₃In₂(PO₄)₃ are isostructural to sodium analogs (β- and α-Na₃In₂(PO₄)₃) and are related to alluaudite (II) and NASICON (III) structure types. Compounds I and II are not stable at temperature above 850 °C. Ag₃In(PO₄)₂ is decomposed providing silver orthophosphate Ag₃PO₄ and α-Ag₃In₂(PO₄)₂. β-Ag₃In₂(PO₄)₃ is transformed to α-Ag₃In₂(PO₄)_3.     

Phase equilibria and crystal chemistry of the R-Cu-Ti-O systems (R=lanthanides and Y)

As part of the study of interaction of the Ba₂RCu₃O_6+z (R=lanthanides and Y) superconductor with SrTiO₃ buffer, phase equilibria of the subsystem, R₂O₃-TiO₂-CuO (R=Nd, Y, and Yb), have been investigated in air at 960 °C. While the phase relationships of the two phase diagrams with smaller R (Y and Yb) are similar, substantial differences were found in the Nd₂O₃-TiO₂-CuO system, partly due to different phase formation in the binary R₂O₃-TiO₂ and R₂O₃-CuO systems. R₂CuTiO₆ and R₂Cu₉Ti₁₂O₃₆ were the only ternary phases established in all the three diagrams. R₂Cu₉Ti₁₂O₃₆ belongs to the perovskite-related [AC₃](B₄)O₁₂ family which is cubic Im3. Depending on the size of R³⁺, R₂CuTiO₆ crystallizes in two crystal systems: Pnma (R=La-Gd), and P6₃cm (R=Dy-Lu). The structure and crystal chemistry of the Pnma series of R₂CuTiO₆ (R=La, Nd, Sm, Eu, and Gd) are discussed in detail in this paper. Patterns for selected members of R₂CuTiO₆ have also been prepared and submitted for inclusion in the Powder Diffraction File (PDF).     

Mixed oxides of sodium, antimony (5+) and divalent metals (Ni, Co, Zn or Mg)

A family of α-NaFeO₂-type oxides Na_xM_(1+x)/3Sb_(2−x)/3O₂ (M=Ni, Co, Zn, Mg; x≈0.8 or 0.9) has been prepared by solid state reactions and characterized by powder XRD. At x=1, ordering occurs with tripling the unit cells and formula units. The powder patterns for Na₃M₂SbO₆ (M=Ni, Co) comply with both trigonal P3₁12 cell and monoclinic C2/m cell. The Ni compound exhibits also a series of extremely weak reflections (I<0.3%) that need doubling of the c axis, and the final cell is C2/c, a=5.3048(3), b=9.1879(4), c=10.8356(7), β=99.390(5). These ambiguities are explained by stacking faults. The compounds absorb atmospheric moisture with c-axis expansion up to 29%. A delafossite-related superlattice Ag₃Co₂SbO₆ has been prepared by ion exchange and refined: P3₁12, a=5.3842(2), c=18.6613(10). Ionic conductivity of the Na_0.8Ni_0.6Sb_0.4O₂ ceramics, 0.4 S/m at 300 °C, is greater than reported previously, presumably owing to the grain orientation produced by hot pressing.     

Atomistic simulation on the site preference and mechanical properties of Th3Co4+xAl12−x and U3Co4+xAl12−x

An atomistic study is presented on the phase stability, site preference and lattice constants of the actinide intermetallic compounds Th₃Co_4+xAl_12−x and U₃Co_4+xAl_12−x. Calculations are based on a series of interatomic pair potentials related to the actinides and transition metals, which are obtained by a strict lattice inversion method. The lattice constants of Th₃Co_4+xAl_12−x and U₃Co_4+xAl_12−x are calculated for different values of x. The site preference of Co atoms at Al sites is also evaluated and the order is given as 6h, 4f, 2b and 12k for Th₃Co_4+xAl_12−x, and 6h, 4f, 12k and 2b for U₃Co_4+xAl_12−x. In addition, some simple mechanical properties such as the elastic constants and bulk modulus are investigated for the actinide compounds with complex structures.