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.     

Thermodynamic and surface properties of Ge–Ga and Ge–Sb liquid alloys

Thermodynamic and surface properties of Ge–Ga and Ge–Sb liquid alloys have been studied using statistical mechanical formulations based on complex formation and that based on the concept of layered structure near the interface. The study showed that low level of complex formation of the form Ge _{2 Sb} exists in Ge–Sb toward the Ge-rich end of the concentration range and the surface properties of Ge–Ga are almost equal to their corresponding bulk equivalent.     

Thermodynamics and vacuum distillation studies of liquid Al–Ga and In–Sn alloys

Activities of components in liquid Al–Ga and In–Sn alloys, the separation coefficients and vapour–liquid phase equilibrium in vacuum distillation were predicted using the molecular interaction volume model as a function of the activity coefficients. The results indicated that both Al and In are preferentially volatilised into vapour phase while Ga and Sn remain in residue. Similarly, we found that both the mass fraction and the content of Al and In in vapour phase increase as distillation temperature increases such that when the content of Al is 0.005985 wt% and In is 0.004141 wt% in vapour phase, respectively, in liquid phase, it was 70 wt% at T = 1073 K for both. The calculated values of activity and activity coefficients at various temperatures are presented. Comparison of the predicted values with experimental data indicates good agreement, thus verifying from statistical thermodynamics viewpoint that the model is stable and reliable.     

Determination of gallium at trace levels using a spectrofluorimetric method in synthetic U–Ga and Ga–As solutions

A simple, easy to use and selective spectrofluorimetric method for the determination of trace levels of gallium has been developed. A new Schiff base, N-o-vanillidine-2-amino-p-cresol (OVAC) was synthesized and its fluorescence activity with gallium investigated. Based on this chelation reaction, a spectrofluorimetric method has been developed for the determination of gallium in synthetically prepared Ga–U and Ga–As samples buffered at pH 4.0 using acetic acid–sodium acetate. The chelation reaction between Ga(III) and N-o-vanillidine-2-amino-p-cresol was very fast, requiring only 30 min at room temperature to complex completely. The limit of detection (LOD) (3σ) for Ga(III) was 7.17 nM (0.50 μg L^?1), determined from the analysis of 11 different solutions of 20 μg L^?1 Ga(III).     

Characterization and Activity of Cr, Cu and Ga Modified ZSM—5 for Direct Conversion of Methane to Liquid Hydrocarbons

Direct conversion of methane using a metal-loaded ZSM-5 zeolite prepared via acidic ion exchange was investigated to elucidate the roles of metal and acidity in the formation of liquid hydrocarbons. ZSM-5 (SiO2/A12O3=30) was loaded with different metals (Cr, Cu and Ga) according to the acidic ion-exchange method to produce metal-loaded ZSM-5 zeolite catalysts. XRD, NMR, FT-IR and N2 adsorption analyses indicated that Cr and Ga species managed to occupy the alllmlnum positions in the ZSM-5 framework. In addition, Cr species were deposited in the pores of the structure. However, Cu oxides were deposited on the surface and in the mesopores of the ZSM-5 zeolite. An acidity study using TPD-NH3, FT-IR, and IR-pyridine analyses revealed that the total number of acid sites and the strengths of the BrSusted and Lewis acid sites were significantly different after the acidic ion exchange treatment.Cu loaded HZSM-5 is a potential catalyst for direct conversion of methane to liquid hydrocarbons. The successful production of gasoline via the direct conversion of methane depends on the amount of aluminum in the zeolite framework and the strength of the BrSnsted acid sites.     

Ga+-catalyzed hydrosilylation? About the surprising system Ga+/HSiR3/olefin,proof of oxidation with subvalent Ga+ and silylium catalysis with perfluoroalkoxyaluminate anions

Already 1 mol% of subvalent [Ga(PhF)₂]⁺[pf]⁻ ([pf]⁻ = [Al(OR^F)₄]⁻, R^F = C(CF₃)₃) initiates the hydrosilylation of olefinic double bonds under mild conditions. Reactions with HSiMe₃ and HSiEt₃ as substrates efficiently yield anti-Markovnikov and anti-addition products, while bulkier substrates such as HSiⁱPr₃ are less reactive. Investigating the underlying mechanism by gas chromatography and STEM analysis, we unexpectedly found that H₂ and metallic Ga⁰ formed. Without the addition of olefins, the formation of R₃Si–F–Al(OR^F)₃ (R = alkyl), a typical degradation product of the [pf]⁻ anion in the presence of a small silylium ion, was observed. Electrochemical analysis revealed a surprisingly high oxidation potential of univalent [Ga(PhF)₂]⁺[pf]⁻ in weakly coordinating, but polar ortho-difluorobenzene of E_1/2(Ga⁺/Ga⁰; oDFB) = +0.26–0.37 V vs. Fc⁺/Fc (depending on the scan rate). Apparently, subvalent Ga⁺, mainly known as a reductant, initially oxidizes the silane and generates a highly electrophilic, silane-supported, silylium ion representing the actual catalyst. Consequently, the [Ga(PhF)₂]⁺[pf]⁻/HSiEt₃ system also hydrodefluorinates C(sp³)–F bonds in 1-fluoroadamantane, 1-fluorobutane and PhCF₃ at room temperature. In addition, both catalytic reactions may be initiated using only 0.2 mol% of [Ph₃C]⁺[pf]⁻ as a silylium ion-generating initiator. These results indicate that silylium ion catalysis is possible with the straightforward accessible weakly coordinating [pf]⁻ anion. Apparently, the kinetics of hydrosilylation and hydrodefluorination are faster than that of anion degradation under ambient conditions. These findings open up new windows for main group catalysis.

Nobler than expected: subvalent [Ga(PhF)₂][pf] ([pf]⁻ = [Al{OC(CF₃)₃}₄]⁻) oxidizes hydrosilanes to silylium ions, allowing for catalytic hydrosilylation and hydrodefluorination and suggesting that silylium catalysis is possible with the [pf]− anion.     

Effects of growth behaviors on chemical and physical properties of sol–gel derived ZnO:Ga films

In this study, we investigated the effects of different heating processes on the structural, electrical and chemical properties of ZnO:Ga (GZO) films from the viewpoint of nucleation and growth behaviors. An infrared heating furnace and a traditional tube furnace were employed for the homogeneous and heterogeneous nucleation of GZO films. XRD patterns demonstrated that the preferential growth orientation of both kinds of GZO films is still the (002) direction. XPS data implied that the infrared heating process enables more uniform distribution of the dopant material and retards the oxidization of gallium in grain boundary areas. At the same time, the textured crystallite might provide a free tunnel for oxygen diffusion. Thus, the activation of free charge carriers could be more efficient when the GZO films were annealed under vacuum. As a result, the samples annealed by the infrared heating furnace had a noticeably high carrier concentration. Although the mobility was slightly smaller than that of the samples annealed by the tube furnace, film resistivity dropped obviously in general.     

Synthesis and characterization of Sibunit-supported Pd–Ga,Pd–Zn,and Pd–Ag catalysts for liquid-phase acetylene hydrogenation

Pd/Sibunit and Pd–M/Sibunit (M = Ga, Zn, or Ag) catalysts have been synthesized, and their catalytic properties in liquid-phase acetylene hydrogenation have been investigated. Doping of the palladium catalyst with a metal M leads to the formation of the Pd₂Ga, PdZn, or Pd_0.46Ag_0.54 bimetallic compound. The bimetallic particles are much smaller (1.6–2.0 nm) than the monometallic palladium particles (4.0 nm). Doping with zinc raises the ethylene selectivity by 25% without affecting the activity of the catalyst. Specific features of the effect of each of the dopants on palladium are reported.     

Comparative thermodynamic study of Ga–In–Sb system

The results of comparative thermodynamic analysis of Ga–In–Sb system are presented in this paper. Investigations, carried out in the section from Ga corner with molar ratio of In:Sb equal to 1:1, were done experimentally, using Oelsen calorimetry at the temperature 873 K and analytically, applying different calculation methods—Toop and Muggianu, in the temperature interval from 873 to 1673 K. Excess molar Gibbs energies and activity of all components in specified temperature interval were calculated.     

Hydroamination of alkynes with aromatic amines catalyzed by digallane (dpp-bian)Ga—Ga(dpp-bian)

Digallane (dpp-bian)Ga—Ga(dpp-bian) (1) (dpp-bian is the 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) catalyzes the addition of 4-chloroaniline to some terminal alkynes RC≡CH (R = Buⁿ, Ph, 4-MeC₆H₄). The reaction orders in each of the substrates were found for the reaction of phenylacetylene with 4-chloroaniline catalyzed by compound 1. The reaction of compound 1 with phenylacetylene in a molar ratio of 1: 10 led to 1-[N-(2,6-diisopropylphenyl)imino]-2-(1-phenylethylidene)acenaphthene (5) and the compound [C₁₂H₆(NC₆H₃Pr₂ ⁱ)(PhC=CH₂)(PhC=CH)]Ga(C≡CPh)₂ (6). The reaction of digallane 1 with phenylacetylene and aniline in a stoichiometric ratio of 1: 2: 2 gave bis-anilide (dpp-bian)-Ga[N(H)Ph]₂ (7) in 40% yield. The compound (PhC≡C)₃Ga·THF (9) was obtained by the reaction of three equivalents of sodium phenylacetylide (prepared in situ from phenylacetylene and sodium) with one equivalent of GaCl₃ in tetrahydrofuran. Compounds 5—7 and 9 were characterized by IR spectroscopy, ¹H NMR spectroscopy was used to characterize products 5, 6, and 9, whereas EPR spectroscopy was used for amide 7. The structures of compounds 5—7 and 9 were determined by single crystal X-ray diffraction analysis.     

Transport and electrocatalytic properties of La0.3Sr0.7Co0.8Ga0.2O3−δ membranes

Incorporation of gallium into the perovskite lattice of La_0.3Sr_0.7CoO_3– leads to increasing unit cell volume and to decreasing thermal expansion, total conductivity and oxygen permeability. At 973–1223 K, the oxygen permeation fluxes through La_0.3Sr_0.7Co_0.8Ga_0.2O_3– ceramics with 96.5% density are determined by the bulk ionic conduction and surface exchange rates. The total conductivity of La_0.3Sr_0.7Co_0.8Ga_0.2O_3–, predominantly p-type electronic, exhibits an apparent pseudometallic behavior due to oxygen losses on heating, whereas the p(O₂) dependencies of the conductivity and Seebeck coefficient suggest a small-polaron mechanism of hole transport. The average thermal expansion coefficients in air are 15.9×10^–6 K^–1 at 360–710 K and 27.9×10^–6 K^–1 at 710–1030 K. On decreasing oxygen pressure down to 4–30 Pa at 973–1223 K, perovskite-type La_0.3Sr_0.7Co_0.8Ga_0.2O_3– transforms into a brownmillerite-like modification, whose electrical properties are essentially p(O₂) independent. Further reduction results in the decomposition of the brownmillerite into a multiphase oxide mixture at p(O₂)=8×10^–10–3×10^–4 Pa, and then in the segregation of metallic cobalt. Due to surface-limited oxygen transport, La_0.3Sr_0.7Co_0.8Ga_0.2O_3– membranes are, however, kinetically stable under an air/CH₄ gradient up to 1223 K. The conversion of dry methane in model membrane reactors increases with oxygen permeation flux and temperature, but yields high CO₂ concentrations (>90%), indicating a dominant role of complete CH₄ oxidation on the membrane surface.     

Calculation of direct and indirect excitons in GaAs–Ga1−xAlxAs coupled double quantum wells: Electric and magnetic fields and hydrostatic pressure effects

A study of the electronic and optical properties of coupled double quantum wells is presented. Within the framework of the effective mass and parabolic-band approximations we have calculated the electron–hole and photoluminescence energy transitions under simultaneous effects of electric and magnetic fields. For that purpose, a variational procedure has been used, taking into account the effect of hydrostatic pressure. The electric field is taken to be oriented along the growth direction of the heterostructure whereas for the magnetic field both in-plane and in-growth directions have been considered. The results show that hydrostatic pressure is a useful tool to tune the direct and indirect exciton transitions in such heterostructures. It is shown that the photoluminescence peak energy transitions strongly depend on the external fields and hydrostatic pressure studied here. Furthermore, our numerical outcome is in good agreement with previous experimental findings at zero pressure in double quantum wells under applied electric and magnetic fields.     

Why Does a Ga2 Dimer React Spontaneously with H2, but a Ga Atom Does Not?—A Detailed Quantum Chemical Investigation of the Differences in Reactivity Between Ga Atoms and Ga2 Dimers,in Combination with Experimental Results

The spontaneous and photoactivated reactions between Ga(2) and H(2) in a matrix of solid Ar at 12 K have been followed by using IR spectroscopy and have been shown to give access to several isomers of the subvalent hydride Ga(2)H(2). We now present Raman spectra for this system, to complete its characterization on the basis of vibrational spectra. In addition, the differences between the reactivity of a Ga atom and a Ga(2) dimer toward H(2) are evaluated. The matrix isolation experiments have shown that Ga(2) reacts spontaneously with H(2,) at 12 K, to give the cyclic subvalent hydride Ga(micro-H)(2)Ga (D(2h) symmetry), which can be transformed into two other isomers of Ga(2)H(2) by selective photoactivation. Interestingly, the spontaneous reaction is subject to a marked isotopic effect. In total, the experimental results provide detailed information about the reaction mechanism. In contrast to Ga(2), Ga atoms do not react spontaneously with H(2); on photoactivation they instead yield the radical species GaH(2). The quantum chemical calculations presented herein start with an analysis of the structures and relative energies of the relevant species at the MP2 level, by using extended basis sets, and lead on to a discussion of the correlation diagrams for both reactions. Finally, CASSCF and MRCI methods, in combination with moderate-sized basis sets, were employed to analyze in detail the mechanisms of the two reactions. It will be shown that the computational results, in concert with the experimental findings, provide a satisfying explanation of the contrasting reactivities of Ga and Ga(2).     

Synthesis,characterization, and biocide activity of new dithiocarbamate-based complexes of In(III), Ga(III), and Bi(III) – Part III

In this work, we describe the syntheses, characterization, and antifungal activity of [In{S₂CNR(R¹)}₃] (1), [Ga{S₂CNR(R¹)}₃] (2), [Bi{S₂CNR(R¹)}₃] (3), [In{S₂CNR(R²)}₃] (4), [Ga{S₂CNR(R²)}₃] (5), and [Bi{S₂CNR(R²)}₃] (6) {R?=?Me; R¹?=?CH₂CH(OMe)₂; and R²?=?2-methyl-1,3-dioxolane}. All complexes have been characterized using infrared and ¹H and ¹³C spectroscopy, and the structures of 1, 3, 4, and 6 have been authenticated by X-ray diffraction. The In(III)–dithiocarbamate bonding scheme depicts a distorted octahedral with asymmetric In(III)–S bonds and S–In–S angles. A pentagonal bipyramid is observed for the corresponding Bi(III) complexes with intermolecular Bi–S associations through the lone pair of electrons. The antifungal activities of 1–6 have been screened against Aspergillus niger, Aspergillus parasiticus, and Penicillium citrinum, and the results have been compared with those of nystatin and miconazole nitrate, as control drugs.     

Synthesis, Characterization and Catalytic Properties of Zeolite [B, Al, Ga, Fe]-ZSM-5

Zeolite [B,Al, Ga, Fe]-ZSM-5, containing several heteroatoms, was synthesized for the first time under. hydrothermal conditions. Characterization of the sample using various techniques such as XRD, IR, ESR, TG-DTA, SEM and XRF indicates that the heteroatoms are located in the framework, similar to the situations of the heteroatoms present in the zeolites [B]-, [Al]-, [Ga]- and [Fe]-ZSM-5. The study of the catalytic properties for reactions of cracking and dehydrogenation of ethylbenzene reveals that the heteroatoms function independently and there are no mutual interactions between the heteroatoms.     

Thermal Analysis of Sulfide Ge—Ga Glasses Doped by Praseodymium

The present study shows the dependence of the temperature of glass transition — T _g upon the presence and quantity of doping Pr atoms. Substantial effect of the form — chemical nature of compound from which the doping atoms are incorporated into the glass has been displayed as well. With the increase of the content of sulfidic form T _g values approach the level of undoped glasses. Thus, if the studied glasses are doped by sulfidic form, bonded areas atoms of Pr so atoms of S. Glasses doped by halogenous source of Pr behave differently; the shift of the T _g value does not change with the amount of the dopand, displaying the anion deficiency of glass stoichiometry in studied interval of halogenous dopands. Generally, a very slight non-stability of the glass against the oxidation in temperature region of glass transition is observed.This revised version was published online in November 2005 with corrections to the Cover Date.     

Insertion of the Ga(I) bis-imidinate Ga(DDP) into the metal halogen bonds of Rh(I) complexes. How electrophilic are coordinated Ga(DDP) fragments?

The reactivity of Ga(DDP) (DDP = 2-((2,6-diisopropylphenyl)amino-4-((2,6-diisopropylphenyl)imino)-2-pentene) towards the rhodium-chloride bonds of [RhCl(PPh3)3] and [RhCl(COE)2]2 (COE = cyclooctene) is investigated. Reaction of the first complex leads to [(Ph3P)2Rh{Ga(DDP)}(mu-Cl)] (1), exhibiting a chloride bridging the gallium and the rhodium atoms, whereas the second complex leads to a full insertion of the Ga(DDP) ligand into the Rh-Cl bond giving [(COE)(benzene)Rh{(DDP)GaCl}] (2) on coordination of the solvent C6H6. Compounds 1 und 2 readily react with the halide abstracting reagent Tl[BArF] (BArF = B[3,5-(CF3)2C6H3]4), yet the products could not be isolated and characterized because of their lability. The Au(I) complex [{(DDP)Ga}Au{Ga(DDP)}Cl] reacts with Na[BArF] giving the linear, symmetric cationic complex [{(DDP)Ga.THF}2Au][BArF] (3.2THF), exhibiting two THF molecules coordinated to the Ga(DDP) moieties.     

Antimicrobial,antifertility, and antiradiation studies of Ga(III) and Tl(I) complexes with N∩S and N ∩ O donor systems

New complexes of gallium(III) and thallium(I) derived from 5,6-dimethyl-1H-indol-2,3-dione hydrazinecarbothioamide (L¹H) and 5,6-dimethyl-1H-indol-2,3-dione hydrazinecarboxamide (L²H) have been prepared and investigated using a combination of microanalytical analysis, melting point, molar conductance measurement, electronic, IR, ¹H NMR, and ¹³C NMR spectral studies. Gallium isopropoxide interacts with the ligands in 1 : 1, 1 : 2, and 1 : 3 molar ratios resulting in the formation of colored products, whereas TlCl forms only unimolar products. The mono- and bis-alkoxy derivatives are dimeric, while the tris ligand metal complexes are monomeric. On the basis of conductance and spectral evidences, a pentacoordinate structure for gallium(III) 1 : 1 complexes, hexacoordinate structure for 1 : 2 and 1 : 3 complexes, and a bicoordinate geometry for thallium(I) complexes have been assigned. The ligands are coordinated to gallium(III) and thallium(I) via the azomethine nitrogen and the thiolic sulfur/enolic oxygen. The antimicrobial activities of the ligands and complexes have been screened in vitro against bacteria Pseudomonas cepacicola and Bacillus subtilis and fungi Collectatrichum capsici and Fusarium oxysporum. The complexes have higher activities than the free bases. In vivo studies of the ligands and their corresponding complexes have also been carried out to assess their antifertility and antiradiation activities. The results of these activities indicate the antiandrogenic and radiation protective nature of these complexes.