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At least 1,261 records · Page 70Linked to original sources
PubMed2003

[2,6-Mes(2)C(6)H(3)](2)Ga(+)Li[Al(OCH(CF(3))(2))(4)](2)(-) (Mes = 2,4,6-Me(3)C(6)H(2)): A compound containing a linear unsolvated two-coordinate gallium cation.

The title compound [2,6-Mes(2)C(2)H(3)](2)Ga(+)Li[Al(OCH(CF(3))(2))(4)](2)(-), 1, containing a linear two-coordinate gallium cation, has been obtained by metathesis reaction of [2,6-Mes(2)C(2)H(3)](2)GaCl with 2 equiv of Li[Al(OCH(CF(3))(2))(4)] in C(6)H(5)Cl solution at room temperature. Compound 1 has been characterized by (1)H, (13)C((1)H), (19)F, and (27)Al NMR spectroscopy and X-ray crystallography. Compound 1 consists of isolated [2,6-Mes(2)C(6)H(3)](2)Ga(+) cations and Li[Al(OCH(CF(3))(2))(4)](2)(-) anions. The C-Ga-C angle is 175.69(7) degrees, and the Ga-C distances are 1.9130(14) and 1.9145(16) A. The title compound is remarkably stable, is only a weak Lewis acid, and polymerizes cyclohexene oxide.

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PubMed2004

Gallium cluster "magic melters".

Calorimetry measurements (using a method based on multicollision induced dissociation) have been performed for unsupported gallium clusters, Gan+ (n = 30-50 and 55). Melting transitions have been identified from spikes in the heat capacities recorded as a function of temperature. There are enormous fluctuations in the melting temperatures and the heats of fusion with cluster size. Clusters with n = 31, 33, 37, and 45-47 are "magic melters" with particularly well-defined melting transitions. There is a strong correlation between the heats of fusion, entropies of fusion, and the stabilities of the clusters. However, these quantities are not strongly correlated with the melting temperatures.

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PubMed2005

Electron flow generated by gas phase exothermic catalytic reactions using a platinum-gallium nitride nanodiode.

We report steady-state conversion of chemical reaction energy into hot electrons by ballistic injection into a platinum-gallium nitride (Pt/GaN) nanodiode during the platinum-catalyzed oxidation of carbon monoxide. Surface catalytic reactions of molecules from the gas phase generated continuous steady-state hot electron currents with energies at least that of Schottky barrier energy ( approximately 1 eV). These hot electron currents were observed on two different nanodiodes (Pt/TiO2 and Pt/GaN) and represent a new method of chemical energy conversion.

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PubMed2005

Polarized Raman confocal microscopy of single gallium nitride nanowires.

Polarized Raman spectra and corresponding Raman scattering intensity images of an isolated gallium nitride nanowire with a diameter of 170 nm are presented. The sensitivity of the confocal microscope combined with a high-resolution piezoelectric stage enables analysis of the crystalline phase and crystallographic orientation of an individual nanowire with an excellent spatial and spectral resolution in a short acquisition time.

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PubMed2005

Liquid gallium columns sheathed with carbon: Bulk synthesis and manipulation.

It is impossible to fabricate isolated gallium nanomaterials due to the low melting point of Ga (29.8 degrees C) and its high reactivity. We report the bulk synthesis of uniform liquid Ga columns encapsulated into carbon nanotubes through high-temperature chemical reaction between Ga and CH4. The diameter of filled Ga liquid columns is approximately 25 nm, and their length is up to several micrometers. The thickness of the carbon sheaths is approximately 6 nm. Simultaneous condensation of a Ga vapor and carbon clusters results in the generation of Ga-filled carbon nanotubes. A convergent 300 kV electron beam generated in a field emission high-resolution electron microscope is demonstrated to be a powerful tool for delicate manipulation of the liquid Ga nanocolumns: they can be gently joined, cut, and sealed within carbon nanotubes. The self-organization of a carbon sheath during the electron-beam irradiation is discussed. The electron-beam irradiation may also become a decent tool for Ga-filled carbon nanotube thermometer calibration.

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PubMed2005

Second-order phase transitions in amorphous gallium clusters.

Ion mobility and calorimetry measurements have been used to probe the nature of the phase transitions in gallium clusters with 29-55 atoms. While most clusters appear to undergo a first-order transition between solidlike and liquidlike phases, a few show the signature of melting without a significant latent heat. These transitions appear to be the finite size analogue of a second-order phase transition, and they presumably occur for some cluster sizes because their solidlike phase is amorphous.

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PubMed2005

Synthesis of sub-20-nm-sized bismuth 1-D structures using gallium-bismuth systems.

Bismuth (Bi) nanowires are interesting one-dimensional systems due to the significant quantum confinement effects exhibited as a function of the wire diameters, and synthesizing Bi nanowires with sizes below 20 nm is of fundamental importance in understanding quantum effects. Here, we report a bulk synthesis method to synthesize ultrafine Bi nanowires and a new morphology of bismuth nanostructures, tapered whiskers. These tapered whiskers are about 10-20 mum in length and have diameters of 5-10 nm at the tip and 250-500 nm at the base. The synthesis method is based upon the multiple nucleation and basal growth of nanometer scale nuclei from molten gallium (Ga) melts that result from the low solubility of Bi in Ga and the low eutectic temperature of the Ga-Bi binary system. Adopting different methods of supplying bismuth and using variations in simple heating and cooling, we have synthesized a variety of bismuth nanostructures.

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PubMed2005

Synthesis and optical properties of gallium phosphide nanotubes.

Gallium phosphide nanotubes with zinc blende structure were synthesized for the first time. The as-prepared GaP nanotubes are polycrystalline with diameters of 30-120 nm and occasionally partially filled. The growth has been reasonably proposed to follow vapor-liquid-solid (VLS) mechanism. The integration of the nanotubular structure with the unique intrinsic semiconducting properties of GaP might bring GaP nanotubes some novel optical and electronic properties and applications.

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PubMed2006

Unusual infrared spectrum of ethane adsorbed by gallium oxide.

The present study reports an unusual diffuse reflection Fourier transform (DRIFT) spectrum of ethane adsorbed by gallium oxide. One of the stretching C-H bands in this spectrum with a maximum at 2753 cm(-1) is more than by 100 cm(-1) shifted toward lower frequencies in comparison with gaseous ethane. In addition, the relative intensity of this band is unusually high. This indicates a very strong polarizability of the corresponding chemical bonds resulting from perturbation of ethane by the low coordinated Ga(3+) cations. The assignment of this band to the very strongly perturbed initially fully symmetric nu(1) C-H stretching vibration is confirmed by a DFT modeling of ethane adsorption by the simplest Ga(2)O(3) cluster. The obtained results also indicate heterolytic dissociative adsorption and dehydrogenation of ethane by Ga(3+) Lewis sites at elevated temperature. This is evidenced by the appearance of new IR bands from zinc alkyl fragments and acidic protons followed by decomposition of resulting zinc ethyl species. In parallel, the most intense IR band at lower frequency from the most strongly polarized C-H chemical bond decreased in intensity. The obtained results indicate that these vibrations are involved in subsequent heterolytic dissociative adsorption. The obtained results demonstrate that, similar to the shifts of C-H stretching vibrations to the low-frequency, intensities of IR C-H stretching bands can be also used as an index of chemical activation of adsorbed paraffins via their polarization by the low-coordinated cations.

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PubMed2006

Quantum chemical study of adsorption and dissociation of H2S on the gallium-rich GaAs (001)-4 x 2 surface.

H(2)S adsorption and dissociation on the gallium-rich GaAs(001)-4 x 2 surface is investigated using hybrid density functional theory. Starting from chemisorbed H(2)S on the GaAs(001)-4 x 2 surface, two possible reaction routes have been proposed. We find that H(2)S adsorbs molecularly onto GaAs(001)-4 x 2 via the formation of a dative bond, and this process is exothermic with adsorption energy of 6.6 kcal/mol. For the first reaction route, one of the H atoms from the chemisorbed H(2)S is transferred to a second-layer As atom and the dissociated SH is inserted into the Ga-As bond with an activation barrier of 8.2 kcal/mol, which is found to be 29.3 kcal/mol more stable than the reactants. For the second case, the dissociated species may insert themselves into the Ga-Ga dimer resulting in the Ga-H-Ga and Ga-HS-Ga bridge-bonded states, which are found to be 29.8 and 22.2 kcal/mol more stable than the reactants, respectively. However, the calculations also show that the activation barrier (16.1 kcal/mol) for chemisorbed H(2)S dissociation through the second route is higher than the transfer of one H atom into a second-layer As atom. As a result, we conclude that sulfur insertion into the Ga-As bond is more kinetically favorable.

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PubMed2005

Light-induced switching between structural forms with different optical properties in a single gallium nanoparticulate.

In a single gallium nanoparticulate, self-assembled (from an atomic beam) in a nanoaperture at the tip of a tapered optical fiber, we have observed reversible light-induced reflectivity changes associated with a sequence of transformations between a number of structural forms with different optical properties, stimulated by optical excitation at nanowatt power levels. The ability to change the optical properties of a nanoparticulate using structural transformations provides a new mechanism for photonic functionality on the nanoscale.

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PubMed2005

Gallium-mediated allyl transfer from bulky homoallylic alcohol to aldehydes via retro-allylation: stereoselective synthesis of both erythro- and threo-homoallylic alcohols.

Retro-allylation of bulky gallium homoallylic alkoxides occurs to generate (Z)- and (E)-crotylgallium reagents stereospecifically, starting from erythro- and threo-homoallylic alcohols, respectively. The (Z)- and (E)-crotylgallium reagents immediately reacted with aromatic aldehydes to afford the corresponding erythro- and threo-homoallylic alcohols, respectively. [reaction: see text]

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PubMed2007

Efficient one-pot synthesis of fluorinated benzimidazolines, benzothiazolines, benzoxazolines, and dihydrobenzoxazinones using gallium(III) triflate as a catalyst.

One-pot synthesis of fluorinated benzimidazolines, benzothiazolines, benzoxazolines, and dihydrobenzoxazinones was easily achieved under mild conditions in high yields and purity through gallium(III) triflate mediated condensation-cyclization. Introduction of fluorine atoms favors the formation of the five-membered heterocycles over seven-membered heterocycles. [reaction: see text].

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PubMed2001

Gallium-boron donor-acceptor bonds.

Examples of compounds with gallium-boron donor-acceptor bonds, HC[MeC(2,6-pri2C6H3)N]2Ga-->B(C6F5)3 3 and (eta 5-C5Me5)Ga-->B(C6F5)3 4 have been prepared by treatment of the free gallanediyls with B(C6F5)3; the structures of both compounds were determined by X-ray crystallography.

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