Thermodynamics of the URuC system

Thermodynamic measurements by the electromotive force method were made on the binary intermetallic phases URu₃ and U₃Ru₅ and on the ternary carbides URu₃C_0.7 and U₂RuC₂ of the URu and the URuC systems between 950 and 1200 K using galvanic cells with CaF₂ single crystal electrolytes: U, UF₃¦CaF₂¦UF₃, URu₃, Ru; U, UF₃¦CaF₂¦UF₃, U₃Ru₅, URu₃; Ru, URu₃, UF₃¦CaF₂¦UF₃, URu₃C_0.7, Ru, C; U, UF₃¦CaF₂¦UF₃, URu₃C_0.7, U₂RuC₂, C. The Gibbs energies of formation of URu₃, U₃Ru₅, URu₃C_0.7 and U₂RuC₂ were evaluated from the measured electromotive force which give ^fΔG^o〈URu₃〉 = −199 100 + 35.9 T J mol^−1fΔG^o〈U₃Ru₅〉 = −398 600 + 43.6 T J mol^−1fΔG^o〈URu₃C_0.7〉 = −192 600 + 2.5 T J mol^−1fΔG^o〈U₂RuC₂〉 = −380 200 + 52.5 T J mol⁻¹ The implications of these thermodynamic data for the behaviour of the fission product ruthenium in irradiated carbide fuels are discussed.     

Comparison of the magnetic properties of MmFeband NdFeB compounds

NdFeB and corresponding MmFeB compounds were studied, the high field magnetization at 4.2 K, the a.c. susceptibility (4.2 < T < 300 K) and the anisotropy field were measured using the singular point detection technique (77 < T < 570 K). At room temperature the anisotropy field of the MmFeB is about 3T, whereas that of NdFeB compounds is about 7T. The MmFeB compounds showed effects due to the cerium (lowering the Curie temperature) as well as due to the neodymium (spin reorientation at low temperatures).     

Trapping of the coordinatively unsaturated organosilicon anion radical Me3SiCCCCSiMe3− by double ate-complex formation with AIR3

Reaction of 1,4-bis(trimethylsilyl)-1,3-butadiyne with AIR₃ and potassium in THF has led to observation of the first examples of persistent radical di-ate complexes, [(R₃Al)(Me₃Si)CCCC(SiMe₃)(AIR₃)]⁻, which have been characterized by ESR spectroscopy.     

First principles search of hard materials within the SiCN ternary system

Starting from C₃N₄ and Si₃N₄ stoichiometries and from the pseudocubic model structure of the former, intermediate phases SiC₂N₄ and Si₂CN₄ are proposed and geometry optimised within density functional built pseudopotential method using both local density (LDA) and generalised gradient approximations (GGA). The ternary compounds are found to be less stable than the two binary systems but the trends in the calculated magnitudes of the bulk moduli B₀ from the fit of the E(V) curves with Birch equation of state: B₀ (SiC₂N₄)=334.5 GPa and B₀ (Si₂CN₄)=270.3 GPa can be interpolated from those of the two extreme compounds: B₀ (C₃N₄)=424.1 GPa and B₀ (Si₃N₄)=219.8 GPa. This translates the chemical role of the substituting element on one hand and allows validating Cohen's semiempirical law relating B₀ to the inverse powers of the average interatomic distances on the other hand. From a mismatch of the chemical bonding in Si(C)NC(Si) chain observed by the electron localisation function (ELF) plot we propose an interpretation for the instability of the intermediate ternary phases. The electronic structure (density of states and band structures) obtained from augmented spherical wave (ASW) calculations of the relaxed structures point to semiconducting behaviour with smaller band gaps for the intermediate phases (∼2 eV, compared with the ∼4 eV gap of binaries).     

Cycloaddition of alkynes RCCR′ with free singlet dimethyl germylene Me2Ge

Alkynes RCCR′ exhibit a high and specific reactivity towards free dimethyl germylene Me₂Ge as a typical singlet heavy carbene analogue. New and novel unsaturated² 4-,5-, and 6-membered germa heterocycles with 1–3 Ge atoms are formed, dependent on R and R′ in the 7 alkynes used. Corresponding reaction mechanisms are proposed.     

Allyldialkyl complexes of ruthenium(IV): Preparation and reductive CC bond formation followed by CH bond activation

New η³-allyldimethyl complexes Ru(η⁵-C₅R₅)(η³-C₃H₅)(CH₃)₂, where R = H or CH₃, are prepared from Ru(η⁵-C₅R₅)(η³-C₃H₅)Br₂ by alkylation with trimethyl-aluminium. The Ru^IV dimethyl complex is thermally converted to the Ru^II 1-methylallyl compound, Ru(η⁵-C₅R₅)(η³-CH₂CHCHCH₃)L, where L = CO or t-C₄H₉NC, with evolution of methane. Kinetic and deuteration studies on the reductive process are also discussed.     

Enantioselective synthesis of allenecarboxylates from phenyl acetates through CC bond forming reactions

A variety of optically active 4,4-disubstituted allenecarboxylic acid methyl esters were prepared from simple α,α-disubstituted phenyl acetate through base treatment of the esters to generate ketenes, followed by successive Horner–Wadsworth–Emmons reaction. The transformation was further developed as a one-pot procedure with satisfactory yields and high enantioselectivity.     

Calorimetric studies of CeCu AND CeMgCu alloys

Using different calorimeters, the following measurements have been carried out.

• 1.(i) The integral enthalpies of mixing of CeCu binary and some CeMgCu ternary liquid alloys,
• 2.(ii) The enthalpy of formation and the enthalpy of melting of the intermetallic compound CeCu₂.
• 3.(iii) The heat content of solid and liquid CeCu₂.

The observed concentration and temperature dependence of the measured values of the enthalpies of mixing as well as the glass-forming abilities of these alloys are explained on the basis of an association model.     

The excess enthalpies of liquid GaGeTe and GaSnTe alloys

The excess enthalpies of the liquid alloys GaGeTe and GaSnTe were measured in a heat-flow calorimeter at 1203 K. The enthalpy surface in the ternary space in both systems is characterized by a valley stretching from the exothermic minimum in the GaTe system to the minima of the GeTe and SnTe systems. The minima in the ternary systems were found in this valley, i.e. on the sections Ga₂Te₃-GeTe and Ga₂Te₃-SnTe. A comparison of the experimental data with those calculated from the excess enthalpies of the constituent binaries with the aid of the Bonnier model, reveals only small deviations. A preliminary investigation was made into the ternary phase diagram of GaSnTe. This system contains the two quasibinary sections Ga₂Te₃-SnTe, GaTe-SnTe and the ternary compound Ga₆SnTe₁₀. The previously reported compounds Ga₂SnTe₃ and GaSnTe₂ do not exist.     

Integral intensities and polarity of vinylic CH bonds of 3,3-disubstituted cyclopropenes

The influence of substituents on the polarity of vinylic CH bonds of 3,3-disubstituted cyclopropenes was studied by analysis of the integral absorption intensities of infrared bands. The influence of intermolecular interactions in solutions of cyclopropenes in non-polar solvents on integral intensities has been determined. The dipole moments of the vinylic bonds were determined starting from infrared band intensities. The experimental data were compared with CNDO/S3 calculations. High sensitivity of intensities and frequencies of the absorption bands to the changes in electron acceptor character of substituent has been found. Correlations were established between dipole moment values of vinylic bonds, determined from experiment and on the basis of CNDO/S3 calculations, as well as between stretching vibrational frequencies on the one hand and values of substituent constants on the other.     

Phase equilibrium diagram of the system MnCrO

A hypothetical oxygen pressure-composition phase diagram and a projection of the oxygen pressure-temperature-composition diagram on the composition triangle were constructed from phase equilibria in the system MnCrO on the basis of the data available in literature. The temperature-composition phase equilibrium diagram of this same system in air was specified. Isomorphism of solid solutions with spinel and hausmannite structure and their intertransformation was studied. Two chemical compounds, MnCr₂O₄ and Cr₄Mn₂₈O₄₈, are supposed to exist in the system.     

Bubble-point pressures of the H2COCO2 system

Bubble-point pressures of the H₂COCO₂ system were measured at temperatures from 253.15 to 303.15 K and pressures up to 9 MPa. Multiple bubble-points were observed within certain limits of hydrogen compositions. The data have been compared with the calculated results by the Redlich-Kwong and the Peng-Robinson equations of state.     

A novel CC bond forming reaction of aryl-and alkenylsilanols. A halogen-free Mizoroki-Heck type reaction

When dimethyl(phenyl)silanol is subjected to on electron-deficient olefin in the presence of a stoichiometric amount of Pd(OAc)₂, substitution of the CH bond of the olefin by a phenyl group on the silanol occurs in 52–86% yields. The reactions of several aryl- and alkenylsilanols with several olefins are also found to proceed in the system of 10 mol% of Pd(OAc)₂, Cu(OAc)₂ (3 mol), LiOAc (2 mol) to give the corresponding products in up to 69% yield.     

Copper(I) promoted CC bond forming reactions: direct activation of allyl alcohols

Allylic alcohols, acetates, carbonates and chlorides can be activated by copper(I) salts towards nucleophilic substitution by carbon nucleophiles under relatively mild conditions.     

The CF bond as a tool in the conformational control of amides

The conformation of 2-fluoro-N-(2-fluoroethyl)-propionamide 4 in the solid state indicates the influence of both a β-fluorine-amide gauche effect and an α-fluoroamide effect. The structure reveals the influence of two recently observed stereoelectronic effects associated with the CF bond, which has resulted in the successful prediction of the solid state conformation of amide 4. A gauche relationship (−69.9°) was observed for atoms N(1)C(4)C(5)F and a syn planar (2.0°) relationship was observed for N(1)C(3)C(2)F. The paper demonstrates the predictive power of using the CF bond as a tool in influencing the conformation of amides and peptides.