Resonance Raman spectrum of the complex [(C2H5)4N] AuBr4

A resonance Raman spectrum of the complex [(C₂H₅)₄N] AuBr₄ has been observed by use of 457.9 nm Ar⁺ excitation. Three progressions in the totally symmetric stretching fundamental ν₁ (a_1g) have been observed, viz. nν₁ (as far as n = 9), ν₂ + nν₁ (as far as n = 1), and ν₄ + nν₁ (as far as n = 6). The spectroscopic constants ω₁ and x₁₁ have been determined from an analysis of the nν₁ and ν₄ + nν₁ progressions.     

Distortion of the coordination polyhedron in mononuclear copper(II) complexes. Optical absorption and electron spin resonance studies on some five-coordinate copper(II) complexes

The preparation and spectral properties are reported for a series of ten mixed-ligand copper(II) complexes of the form [Cu(A)(B)_n](X), where A is acetylacetonate anion, B represents a mono- or bidentate ligand such as morpholine, piperidine, isonicotinic acid hydrazide, 2,2′-bipyridine, 1,10-phenanthroline and X is variously NO^?₃ or ClO^?₄ anion and n = 1 or 2. The coordination of the anions and ligands has been demonstrated by infrared and electronic spectral methods. Electron spin resonance spectral data show the square-pyramidal five-coordinated arrangement around copper(II) in these complexes. Parameters such as g₆, g_⊥, A₆, A_⊥, 〈g〉 and 〈A〉 calculated from electron spin resonance data in solid and solution state at room temperature as well as frozen solution indicate the presence of the unpaired electron in the d_x2_?y2 or d_z2 orbital. These results are in good agreement with electronic and photoacoustic spectral studies.     

Synthesis of perovskite-related layered AnBnO3n+2 = ABOX type niobates and titanates and study of their structural,electric and magnetic properties

ABO_X niobates and titanates belonging to the homologous series A_nB_nO_3n+2 are a special group of perovskite-related layered materials. These oxides comprise the highest-T_c ferroelectrics such as CaNbO_3.50 and LaTiO_3.50, as well as thermodynamically stable bulk compounds involving well-ordered stacking sequences of layers with different thickness such as SrNbO_3.45. An extensive overview on many ABO_X compositions of the A_nB_nO_3n+2 family and its properties is presented. The crystal structure type is given by n and can be tuned by adjusting the oxygen content X. The charge carrier concentration of the electrical conducting oxides can be varied by appropriate substitutions at the A or B site. To investigate the properties of these systems, more than 150 different compositions were prepared. Most of them were grown by floating zone melting, of which many were fabricated as single crystals with precise control of the oxygen content X. For these crystalline compounds, the synthesis, structural, electric and magnetic features are discussed. Attempts to prepare series members beyond the known structure types n=4, 4.33, 4.5, 5 and 6 were not successful. For some of the known structures types n, however, pronounced non-stoichiometric homogeneity ranges with respect to the oxygen content X and cation ratio A/B were found. Thus, these systems offer many possibilities to vary the compositional, structural, chemical and physical properties. Further, measurements of the resistivity as a function of temperature T are reported for crystals of the n=4 type Sr_0.8La_0.2NbO_3.50, n=4.5 type Sr_0.96Ba_0.04NbO_3.45 and n=5 types Sr_1−YLa_YNbO_3.41 (Y=0, 0.035, 0.1), Sr_0.95NbO_3.37, CaNbO_3.41 and LaTiO_3.41. These measurements, which were performed in the temperature range 4 K≤T≤290 K and along the a-, b- and c-axis, revealed a highly anisotropic conductivity and intricate behavior. In parts of the temperature range, these materials are quasi-1D metals which display temperature-driven metal-semiconductor transitions at lower temperatures. The niobates and titanates investigated represent a new group of quasi-1D metals which are in compositional, structural and electronical proximity to non-conducting layered (anti)ferroelectrics. Furthermore, measurements of the magnetic susceptibility as a function of temperature are reported for many compounds. As a typical property at elevated temperatures, it was observed that the magnetic susceptibility rises with increasing temperature.     

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.     

A mechanistic study of the acid- and base-catalysed cleavages of β-trimethylstannylstyrenes

The cleavages of cis- and trans-PhCHCHSnMe₃ in 1/10 AcOD-MeOD have been shown to give cis- and trans-PhCHCHD, respectively. The rates of cleavage of some XC₆H₄CHCHSnMe₃ compounds in 1/10 AcOH-MeOH at 50°C have been measured; there is no significant difference between the rates for cis- and trans-PhCHCHSnMe₃, and the relative rates of cleavage as X is varied are (X  H), 1.0; p-OMe, 7.0; p-Me, 2.3; m-Cl, 0.34; m-Br, 0.36. There is an excellent correlation with σ⁺ constants, with a ρ value of 1.1. The results are interpreted in terms of rate-determining proton transfer to the β-carbon atoms, and it is suggested that acid cleavages of vinylHgX bonds involve analogous mechanisms. PhSnMe₃ is cleaved 20 times as slowly as PhCHCHSnMe₃ in the 1/10 AcOH/MeOH.The rates of cleavage of XC₆H₄CHCHSnMe₃ compounds by a mixture of MeOH (3 vol.) and 2 M aqueous NaOH (2 vol.) have been measured; trans-PhCHCHSnMe₃ is cleaved about 1.3 times as rapidly as its cis-isomer, and about 12 times as rapidly as a mixture of cis- and trans-PhCHCHSnEt₃. The relative rates for the various XC₆H₄CHCHSnMe₃ compounds (mainly trans-isomers) are (X ) H, 1.0; p-OMe, 0.99; p-Me, 0.92; m-Cl, 1.67; m-Br, 1.65. Cleavage of trans-PhCHCHSnMe₃ by NaOD/D₂O/MeOD gives exclusively trans-PhCHCHD. For cleavages in methanolic NaOMe the values of the rate isotope effects, (the ratio k_meOH/k_MeOD) are 2.3–2.6, and those of the product isotope effects, PIE (the product ratio RH/RD on cleavage of RSnMe₃ by NaOMe in 1 : 1 MeOH/MeOD) are 4.5–5.0.The results are interpreted in terms of proton transfer from the solvent to the leaving carbon atom in the rate determining step as the SnC bond breaks as a result of the attack of the base anion at tin in a prior or synchronous process. PhCHCHSnMe₃ is cleaved by the aqueous alcoholic base about 5 times as rapidly as PhSnMe₃.Cleavage of trans-PhCHCHSnMe₃ by PHCOCl in presence of AlCl₃ in CH₂Cl₂ gives trans-PhCHCHCOPh, and cleavage of a 90/10 mixture of trans- and cis-PhCHCHSnMe₃ by bromine in CCl₄ gives a corresponding mixture of trans- and cis-PhCHCHBr.     

Normalized potential sweep voltammetry: Part III. Elimination of the effect of uncompensated Resistance and the application to heterogeneous kinetics of rapid charge-transfer processes

Uncompensated resistance (R_u) has a distoring effect on normalized potential sweep voltammetry (NPSV) slopes. This provides a simple and effective method to determine R_f^o, the value of the potentiostat feedback resistance necessary for full compensation. If the NPSV range is divided into overlapping segment, 1 and 2, corresponding to I_N of 0.20–0.50 and 0.50–0.80 respectively, the slopes m₁ and m₂ differ significantly when R_f differs form R_f^o. The difference, m₁-m₂, is negative for R_f<R_f^o and positive for R_f>R_f^o. Fine tuning of the potentiostat R_f setting so that the average value of the difference is the theoretical value can be accomplished in a minimum of time. Under these conditions, m₁ and m₂, as well as m_T, the slope of the entire correlation have very nearly the same values. Linear equations were derived from theoretical data which allow heterogeneous rate constants to be obtained directly from NPSV slopes. The precision in the NPSV slopes was observed to be of the order of ±0.002 which implies that the method should give reliable rate constants as great as 10cm s^? at a voltage sweep rate of 100V s^?1. The method is demonstrated using the reduction of benzonitrile and perylene in N,N-dimethylformamide and acetonitrile as examples.     

(Mn,Cu)3O4-based conductive coatings as effective barriers to high-temperature oxidation of metallic interconnects for solid oxide fuel cells

(Mn,Cu)₃O₄-based conductive oxides are examined as protective coatings to improve the surface stability of metallic interconnects for solid oxide fuel cells at high temperatures. Nano-sized Mn_3???x Cu _x O₄ materials with various Cu contents (x?=?1.0–1.5) are synthesized and a composition-structure–property relationship is experimentally determined. The Cu content (x) has a significant influence on phase stability as well as sintering, electrical, and thermal expansion characteristics. Thin and dense Mn_3???x Cu _x O₄ coatings are fabricated on the interconnects (Crofer 22 APU) by a slurry coating process and subsequent heat treatment. The coated interconnects exhibit area-specific resistances as low as 7.1–15.0 mΩ cm² at 800 °C. The electrochemical cell shows no performance degradation in the presence of the Mn_3???x Cu _x O₄-coated interconnect. The results indicate that the Mn_3???x Cu _x O₄ coatings act as an effective barrier to high-temperature oxidation of the metallic interconnects.     

Synthesis and fluorescence properties of covalently linked homo- and hetero-porphyrin dyads containing meso-tolyl porphyrin and meso-furyl porphyrin sub-units

Three porphyrin building blocks with N₄, N₃S and N₂S₂ cores having three meso-furyl groups and one meso-iodophenyl group were synthesized and characterized. The porphyrin building blocks were used to synthesize six porphyrin dyads such as N₄-N₄, N₃S-N₃S, N₂S₂-N₂S₂, N₄-N₃S, N₄-N₂S₂ and N₃S-N₂S₂ containing meso-tolyl and meso-furyl porphyrin sub-units under mild Pd(0) mediated coupling conditions. Steady state fluorescence studies indicated an efficient energy transfer from the meso-tolyl porphyrin sub-unit to the meso-furyl porphyrin sub-unit in all six dyads. This study supported the argument that the meso-furyl porphyrins can be used as good energy acceptors when meso-aryl porphyrins act as energy donors in their metal free form.     

Monoelemental polymers: Structure and properties

Monoelemental polymers with various chemical constitutions and different spatial structures (linear Te _n , Se _n , and S _n ; planar graphite C _n , black phosphorus P _n , As _n , Sb _n , and Bi _n ; and chemically bonded three-dimensional diamond C _n , B _n , Si _n , and Ge _n ) were considered and categorized as a class of covalent macromolecular compounds. Quantitative expressions relating the thermal (melting point, thermal expansion coefficient, heat conductivity) and elastic (microhardness, bulk compression modulus of elasticity) properties of polymers to the energy of intra-and intermolecular interactions and the equilibrium length of chemical bonds in the crystalline and glassy states are given. A numerical correlation between the spatial structure of polymers and their thermal and elastic properties was obtained. The hypothetical melting point of diamond at normal pressure was calculated as T _f = 3155 K.     

Properties of MgB2 bulks after combined doping with Fe and C by adding Iron(II) lactate (C6H10FeO6)

Bulk MgB₂ doped with C and Fe was prepared by using the solid state sintering method with C₆H₁₀FeO₆ as dopant. The phase composition, microstructure, and superconducting properties were studied. X-ray diffraction (XRD) shows the presence of iron after the doping. The addition of C₆H₁₀FeO₆ increases the a- and c-axis parameters of MgB₂, as evidenced by the shifting of the (100) and (002) peaks to a lower angle on the XRD patterns. Fe atoms were distributed uniformly, as shown by the field emission scanning electron microscope images, while the magnetization of the sample was dominated by the signals from the MgB₂ superconductor, although the iron-containing materials also contributed a minor amount of magnetization. The residual resistivity ratio was decreased as the C₆H₁₀FeO₆ doping level increased. The critical temperature also decreased with increased doping level, as did the critical current density, J_c. The doping also caused decreases in the irreversibility field, H_irr, and the upper critical field, H_c2. The decrease in H_c2 and H_irr, together with the harmful effects from impurity phases such as MgO is the reason for the decrease in J_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? .     

Synthesis, crystal structure and magnetic properties of the spin ladder compounds La2(Cu1−xZnx)2O5 and La8(Cu1−xZnx)7O19

The influence of Zn-doping on the crystal structure and magnetic properties of the spin ladder compounds La₂Cu₂O₅ (4-leg) and La₈Cu₇O₁₉ (5-leg) have been investigated. The La₂(Cu_1−xZn_x)₂O₅ and La₈(Cu_1−xZn_x)₇O₁₉ solid solutions were obtained as single phases with x=0-0.1 via the solid-state reaction method in the temperature range between 1005-1010 °C and 1015-1030 °C in oxygen and air atmospheres, respectively. The lattice parameters a and c of the monoclinic crystal structures as well as the unit cell volume V increase with increasing x, while b and β decrease for both series. The magnetic susceptibilities χ of both series show a very similar behavior on temperature as well as on Zn-doping, which is supposed to be due to the similar Cu-O coordination in both La₂Cu₂O₅ and La₈Cu₇O₁₉. For low Zn-doping (x?0.04), a spin-chain like behavior is found. This quasi-one-dimensional behavior is strongly suppressed in both series for x?0.04. Here, the maximum (characteristic for spin chains) in χ(T) disappears and χ(T) decreases monotonically with increasing temperature.     

Distribution de la densite des electrons de valence dans Cu2As

The distribution of valency electron density in Cu₂As (C38) has been determined by Fourier synthesis using as coefficients the values ΔF = F_obs ? F_core (F_core corresponds to the structure factors of the inner orbitals). The bonding between the pyramidal-site copper atoms and the arsenic atoms is exposed, as well as the bonding between tetrahedral-site and pyramidal-site copper atoms.The structural evolution of the unit cell from the Cu₂Sb-type (C38) to the Fe₂P-type (C22) and Co₂P-type (C23) can be related to the metal-metalloid interaction. This interaction mainly involves the pyramidal-site metal atoms in the Cu₂Sb-type, and the tetrahedral-site metal atoms in the Fe₂P- and Co₂P-types.     

3DOM InVO4-supported chromia with good performance for the visible-light-driven photodegradation of rhodamine B

Three-dimensionally ordered macroporous (3DOM) monoclinic InVO₄ and its supported chromia (yCrO_x/3DOM InVO₄, y denotes as the weight percentage of Cr₂O₃, y = 5, 10, 15, and 20 wt%) photocatalysts were fabricated using the ascorbic acid-assisted polymethyl methacrylate-templating and incipient wetness impregnation methods, respectively. Physicochemical properties of the materials were characterized by means of a number of analytical techniques. Photocatalytic activities of the samples were evaluated for the degradation of rhodamine B (RhB) in the presence of H₂O₂ under visible-light illumination. Compared to 3DOM InVO₄ and 15CrO_x/bulk InVO₄, yCrO_x/3DOM InVO₄ showed much better visible-light-driven photocatalytic performance for RhB degradation, with the 15CrO_x/3DOM InVO₄ sample performing the best. It is concluded that the CrO_x loading, higher surface area and surface oxygen vacancy density and lower bandgap energy as well as the better quality of 3DOM structure were responsible for the good photocatalytic performance of 15CrO_x/3DOM InVO₄ for the degradation of RhB.     

Some binuclear complexes of iron and cobalt with isocyanide ligands

Whereas Co₂(CO)₈ and RNC (R= Me, Et, and Cy) react to give mixtures of [(RNC)₅Co] [Co(CO)₄] and the covalent, carbonyl-bridged [(RNC)_mCo₂(CO)_8?m] derivatives (m = 1–3), [(π-dienyl)Fe(CO)₂]₂ give only [(π-dienyl)₂Fe₂(CO)_4?n(CNR)_n] complexes (dienyl = C₅H₅, MeC₅H₄ and C₉H₇; n = 1–2) that exist in solution as mixtures of cis- and trans-CO- and RNC-bridged tautomers with the μ-RNC species decreasing in importance as the bulk of R increases.     

Formation enthalpies of rare earth titanate pyrochlores

High-temperature oxide melt solution calorimetry and Rietveld refinements of powder X-ray diffraction data were used to investigate the structure (Fd3m; Z=8) and energetics of a series of RE₂Ti₂O₇ (RE=Sm-Lu) compounds with the pyrochlore structure as well as La₂Ti₂O₇ with a layered perovskite-type structure. All of the RE-titanates were found to be stable in enthalpy with respect to their oxides. In the pyrochlore series, Lu₂Ti₂O₇ was least stable in enthalpy (ΔHf-ox at 298 K=−56.0±4.0 kJ/mol); the most stable materials were Gd-, Eu-, and Sm₂Ti₂O₇ with ΔHf-ox at 298 K=−113.4±2.7, −106.1±4.2, −115.4±4.2 kJ/mol, respectively. In general, as the radius ratio of the A- to B-site cations, R_A/R_B, decreases, the pyrochlore structure becomes less stable. The trend of ionic radius of the RE³⁺ cation vs. ΔHf-ox at 298 K is non-linear and approximately parallels the increasing “resistance” to ion-beam-induced amorphization as R_A/R_B decreases.     

Photochemicalsyn-anti isomerization of a Schiff base: A two-dimensional description of a conical intersection in formaldimine

The shape of theS ₀,S ₁, andT ₁ potential energy surfaces of formaldimine, CH₂=NH, is explored in the two-dimensional subspace defined by the twisting and linear inversion motions which correspond to the geometricalsyn-anti isomerization, using anab initio large-scale CI method. Minima in theS ₁ andT ₁ surfaces as well as aS ₀-S ₁ conical intersection are identified and the photoisomerization mechanism is discussed.     

Synthesis, Structures, and Thermal Expansion of the La2W2−xMoxO9 Series

The La₂W_2−xMo_xO₉ series has been synthesized by the ceramic method. An alternative synthesis using microwave radiation is also reported. La₂W₂O₉ has two polymorphs and the low-temperature phase (α) transforms to the high-temperature form (β) at 1077°C. The influence of the W/Mo substitution in this phase transition has been investigated by DTA. The β structure for x≥0.7 compositions can be prepared as single phase at any cooling rate. The β phase for 0.3≤x≤0.7 compounds can be prepared as single phase by quenching, whereas a mixture of α and β phases is obtained by slow cooling. The W/Mo ratio in both coexisting phases is different with the β-phase having a higher Mo content. The x=0.1 and 0.2 compounds have been prepared as mixtures of phases. The room temperature structure of β-La₂W_1.7Mo_0.3O₉ has been analyzed by the Rietveld method in P2₁3 space group. The final R-factors were R_WP=9.0% and R_F=5.6% with a structure similar to that of β-La₂Mo₂O₉. Finally, the thermal expansion of both types of structures has been determined from a thermodiffractometric study. The thermal expansion coefficients were 2.9×10⁻⁶ and 9.7×10⁻⁶°C⁻¹ for α-La₂W₂O₉ and β-La₂W_1.2Mo_0.8O₉, respectively.     

Ternary rare-earth alumo-silicides—single-crystal growth from Al flux, structural and physical properties

A number of rare-earth alumo-silicides (R-Al-Si) have been synthesized from the corresponding elements by high-temperature reactions, carried out in excess of aluminum to serve as a flux. Under these experimental conditions, large single crystals of all R-Al-Si ternary phases were readily produced. The crystal structures these ternaries adopt were studied by means of powder and single-crystal X-ray diffraction and were classified as follows: (1) the early rare-earths (R=La, Ce, Pr, Nd, Sm, Gd) yield RAl_xSi_2−x, x∼1, non-stoichiometric ternary derivatives of the body-centered α-ThSi₂-type; (2) the late rare-earths (R=Tb, Dy, Ho, Er, Tm) form stoichiometric R₂Al₃Si₂ compounds that crystallize in the C-centered monoclinic Y₂Al₃Si₂-type; (3) the divalent Eu and Yb produce EuAl₂Si₂ and YbAl₂Si₂ with the trigonal CaAl₂Si₂-type, whereas the last lanthanide element, Lu, forms LuAlSi with C-centered orthorhombic YAlGe-type. These structural trends are reviewed, and the evolution of the basic physical properties such as magnetism, heat capacity and electrical resistivity when moving across the series is described in detail.