Showing papers on "Halide published in 2013"

First-Principles Modeling of Mixed Halide Organometal Perovskites for Photovoltaic Applications

Abstract: We computationally investigate organometal CH3NH3PbX3 and mixed halide CH3NH3PbI2X perovskites (X = Cl, Br, I), which are key materials for high efficiency solid-state solar cells. CH3NH3PbX3 perovskites exhibited the expected absorption blue shift along the I → Br → Cl series. The mixed halide systems surprisingly showed the CH3NH3PbI3 and the CH3NH3PbI2Cl (or CH3NH3PbI3–xClx) perovskites to have similar absorption onset at ∼800 nm wavelength, whereas CH3NH3PbI2Br absorbs light below ∼700 nm. To provide insight into the structural and electronic properties of these materials, in light of their application as solar cell active layers, we perform periodic DFT calculations on the CH3NH3PbX3 and CH3NH3PbI2X perovskites. We find a good agreement between the calculated band structures and the experimental trend of optical band gaps. For the mixed halide perovskites our calculations show the existence of two different types of structures with different electronic properties, whose relative stability varies by v...

MAPbI3-xClx Mixed Halide Perovskite for Hybrid Solar Cells: The Role of Chloride as Dopant on the Transport and Structural Properties

Abstract: Hybrid halide perovskites represent one of the most promising solutions toward the fabrication of all solid nanostructured solar cells, with improved efficiency and long-term stability. This article aims at investigating the structural properties of iodide/chloride mixed-halide perovskites and correlating them with their photovoltaic performances. We found out that, independent of the components ratio in the precursor solution, Cl incorporation in an iodide-based structure, is possible only at relatively low concentration levels (below 3–4%). However, even if the material band gap remains substantially unchanged, the Cl doping dramatically improves the charge transport within the perovskite layer, explaining the outstanding performances of meso-superstructured solar cells based on this material.

Mechanism and Selectivity in Nickel-Catalyzed Cross-Electrophile Coupling of Aryl Halides with Alkyl Halides

Abstract: The direct cross-coupling of two different electrophiles, such as an aryl halide with an alkyl halide, offers many advantages over conventional cross-coupling methods that require a carbon nucleophile. Despite its promise as a versatile synthetic strategy, a limited understanding of the mechanism and origin of cross selectivity has hindered progress in reaction development and design. Herein, we shed light on the mechanism for the nickel-catalyzed cross-electrophile coupling of aryl halides with alkyl halides and demonstrate that the selectivity arises from an unusual catalytic cycle that combines both polar and radical steps to form the new C–C bond.

Bimetallic Oxidative Addition Involving Radical Intermediates in Nickel-Catalyzed Alkyl–Alkyl Kumada Coupling Reactions

Abstract: Many nickel-based catalysts have been reported for cross-coupling reactions of nonactivated alkyl halides. The mechanistic understanding of these reactions is still primitive. Here we report a mechanistic study of alkyl–alkyl Kumada coupling catalyzed by a preformed nickel(II) pincer complex ([(N2N)Ni–Cl]). The coupling proceeds through a radical process, involving two nickel centers for the oxidative addition of alkyl halide. The catalysis is second-order in Grignard reagent, first-order in catalyst, and zero-order in alkyl halide. A transient species, [(N2N)Ni-alkyl2](alkyl2-MgCl), is identified as the key intermediate responsible for the activation of alkyl halide, the formation of which is the turnover-determining step of the catalysis.

Halide Anions as Shape-Directing Agents for Obtaining High-Quality Anisotropic Gold Nanostructures

Abstract: The fundamental role of halide anions in the seed-mediated synthesis of anisotropic noble metal nanostructures has been a subject of debate within the nanomaterials community. Herein, we systematically investigate the roles of chloride, bromide and iodide anions in mediating the growth of anisotropic Au nanostructures. A high-purity surfactant solution of hexadecyltrimethylammonium bromide (CTABr) is used to reliably probe the role of each halide anion without interference from impurities. Our investigation reveals that bromide anions are required for the formation of Au nanorods, while the controlled combination of both bromide and iodide anions are necessary for the production of high-quality Au nanoprisms. Chloride anions, however, are ineffective at promoting anisotropic architectures and are detrimental to nanorod and/or nanoprism growth at high concentrations. We examine the seed structure and propose a growth model based on facet-selective adsorption on low-index Au facets to rationalize the nanost...

High temperature atomic layer deposition of silicon oxide thin films

Abstract: Atomic layer deposition (ALD) process formation of silicon oxide with temperature > 500°C is disclosed. Silicon precursors used have a formula of: I. R 1 R 2 m Si(NR 3 R 4 ) n X p wherein R 1 , R 2 , and R 3 are each independently selected from hydrogen, a linear or branched C 1 to C 10 alkyl group, and a C 6 to C 10 aryl group; R 4 is selected from, a linear or branched C 1 to C 10 alkyl group, and a C 6 to C 10 aryl group, a C 3 to C 10 alkylsilyl group; wherein R 3 and R 4 are linked to form a cyclic ring structure or R 3 and R 4 are not linked to form a cyclic ring structure; X is a halide selected from the group consisting of Cl, Br and I; m is 0 to 3; n is 0 to 2; and p is 0 to 2 and m+n+p = 3; and II R 1 R 2 m Si(OR 3 ) n (OR 4 ) q X p wherein R 1 and R 2 are each independently selected from hydrogen, a linear or branched C 1 to C 10 alkyl group, and a C 6 to C 10 aryl group; R 3 and R 4 are each independently selected from a linear or branched C 1 to C 10 alkyl group, and a C 6 to C 10 aryl group; wherein R 3 and R 4 are linked to form a cyclic ring structure or R 3 and R 4 are not linked to form a cyclic ring structure; X is a halide atom selected from the group consisting of Cl, Br and I; m is 0 to 3; n is 0 to 2; q is 0 to 2 and p is 0 to 2 and m+n+q+p = 3.

Optoelectronic devices with organometal perovskites with mixed anions

Abstract: The invention provides an optoelectronic device comprising a mixed-anion perovskite, wherein the mixed-anion perovskite comprises two or more different anions selected from halide anions and chalcogenide anions. The invention further provides a mixed-halide perovskite of the formula (I) [A][B][X] 3 wherein: [A] is at least one organic cation; [B] is at least one divalent metal cation; and [X] is said two or more different halide anions. In another aspect, the invention provides the use of a mixed-anion perovskite as a sensitizer in an optoelectronic device, wherein the mixed-anion perovskite comprises two or more different anions selected from halide anions and chalcogenide anions. The invention also provides a photosensitizing material for an optoelectronic device comprising a mixed-anion perovskite wherein the mixed-anion perovskite comprises two or more different anions selected from halide anions and chalcogenide anions.

Efficient Chromium(II)-Catalyzed Cross-Coupling Reactions between Csp2 Centers

Abstract: Low-toxicity chromium(II) chloride catalyzes at 25 °C within minutes the coupling reactions of various (hetero)arylmagnesium reagents with N-heterocyclic halides, aromatic halogenated ketones or imines, and alkenyl iodides. Remarkably, much lower amounts of homo-coupling side products are obtained compared to related iron, cobalt, or manganese cross-couplings.

Synthesis, Characterization, and Photophysical Properties of Heteroleptic Copper(I) Complexes with Functionalized 3-(2′-Pyridyl)-1,2,4-triazole Chelating Ligands

Abstract: A new series of mononuclear copper(I) complexes (1–9) with functionalized 3-(2′-pyridyl)-1,2,4-triazole chelating ligands, as well as the halide and/or phosphine ancillary ligands, have been synthesized. Complexes 1–9 were fully characterized by elemental analysis, NMR spectroscopy, mass spectroscopy, electronic absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry, and X-ray crystallography (1–8). They adopt a distorted tetrahedral configuration, and are considerably air-stable in solid state and in solution. All these Cu(I) complexes display a comparatively weak low-energy absorption in CH2Cl2 solution, assigned to charge-transfer transitions with appreciable MLCT character, as supported by TD-DFT studies. Cu(I) halide complexes 1–4 each shows bright solid-state emission at room temperature, although they are nonemissive in fluid solutions, in which the emission markedly depends on the halide and the substituent on the 2-pyridyl ring. Complexes 5–9 bearing 2-pyridyl functionalized 1,2,4...

Tuning of gallery heights in a crystalline 2D carbon nitride network

Abstract: Poly(triazine imide)—a 2D layered network—can be obtained as an intercalation compound with halides from the ionothermal condensation of dicyandiamide in a eutectic salt melt. The gallery height of the intercalated material can be tuned via the composition of the eutectic melt and by post-synthetic modification. Here, we report the synthesis of poly(triazine imide) with intercalated bromide ions (PTI/Br) from a lithium bromide and potassium bromide salt melt. PTI/Br has a hexagonal unit-cell (P63cm (no. 185); a = 8.500390(68) A, c = 7.04483(17) A) that contains two layers of imide-bridged triazine (C3N3) units stacked in an AB-fashion as corroborated by solid-state NMR, FTIR spectroscopy and high-resolution TEM. By comparison with a recently reported material PTI/Li+Cl−, prepared from a LiCl/KCl eutectic, the layer-stacking distance in the analogous bromide material was expanded from 3.38 A to 3.52 A – an exceptionally large spacing for an aromatic, discotic system (cf. graphite 3.35 A). Subsequent treatment of PTI/Br with concentrated ammonium fluoride yields poly(triazine imide) with intercalated fluoride ions (PTI/F) (P63/m (no. 176); a = 8.4212(4) A, c = 6.6381(5) A) as a statistical phase mix with PTI/Br. Fluoride intercalation leads to a contraction of the gallery height to 3.32 A, demonstrating that the gallery height is synthetically tuneable in these materials.

Remarks on Ion Generation for CPC Detection Efficiency Studies in Sub-3-nm Size Range

Abstract: To calibrate a newly developed condensation particle counter, samples of known chemical composition are needed as the chemistry plays a role in the activation process. For that, we have built a calibration setup and produced ammonium sulfate, sodium chloride, tungsten oxide, silver, alkyl halide, and ionic liquid clusters down to 1 nm in mobility diameter in positive and negative mode. The chemical composition of most negatively charged clusters was solved using high-resolution mass spectrometer and we identified about 70% of the total signal of the mass spectrometer. For the Airmodus Particle Size Magnifier, which was the instrument to be calibrated, we measured cutoff diameters of 1.1, 1.3, 1.4, 1.6, and 1.6–1.8 nm for negative sodium chloride, ammonium sulfate, tungsten oxide, silver, and positive organics, respectively. From the alkyl halide and ionic liquid experiments, we concluded that the composition plays a bigger role than the charge state of the cluster in the activation process. We also showed...

Multimodal bioimaging using a rare earth doped Gd2O2S:Yb/Er phosphor with upconversion luminescence and magnetic resonance properties

Abstract: While infrared upconversion imaging using halide nanoparticles is very common, the search for very efficient halide free upconverting phosphors is still lacking. In this article we report Gd2O2S:Yb/Er, YbHo, YbTm systems as very efficient alternative phosphors that show upconversion efficiency comparable to or even higher than those of existing halide phosphors. While the majority of rare earth dopants provide the necessary features for optical imaging, the paramagnetic Gd ion also contributes to the magnetic imaging, thereby resulting in a system with bimodal imaging features. Results from imaging of the nanoparticles together with aggregates of cultured cells have suggested that imaging of the particles in living animals may be possible. In vitro tests revealed no significant toxicity because no cell death was observed when the nanoparticles were in the presence of growing cells in culture. Measurement of the magnetization of the phosphor shows that the particles are strongly magnetic, thus making them suitable as an MRI agent.

Medium and high oxidation state metal/non-metal fluoride and oxide–fluoride complexes with neutral donor ligands

Abstract: While most high and medium oxidation state (O.S. ≥ 3) metal and non-metal fluorides and oxide fluorides are strong Lewis acids, exploration of their coordination chemistry with neutral ligands has been limited and mostly non-systematic. This is despite the very different properties conferred on the acceptor centre by the small electronegative fluoride ligands compared to the heavier halides. This article sets out these key differences, discusses possible synthetic routes, the key characterisation techniques, and appropriate bonding models. Current knowledge of the coordination chemistry of d, f and p-block fluorides and oxide fluorides with neutral ligands (with donor atoms drawn from Groups 15 and 16 and including N-heterocyclic carbenes) is then presented and discussed, and the differences in properties compared to complexes containing the heavier halides are illustrated. The emphasis is on work published post 1990, but earlier work is also included as essential background and where no more recent information exists. Attention is drawn to unexplored areas meriting investigation and to possible applications of these complexes.

Copper-catalyzed aromatic C–H bond halogenation with lithium halides under aerobic conditions

Abstract: A concise and practical Cu-catalyzed protocol for the preparation of chloro- and bromoarenes via C–H bond activation has been developed. The advantages of this strategy are the employment of cheap Cu(NO3)2·3H2O, LiX and O2, and its compatibility with both electron-donating and electron-withdrawing substituents on aryl rings.

Method and apparatus for germanium tin alloy formation by thermal cvd

Abstract: A method and apparatus for forming semiconductive semiconductor-metal alloy layers is described. A germanium precursor and a metal precursor are provided to a chamber, and an epitaxial layer of germanium-metal alloy, optionally including silicon, is formed on the substrate. The metal precursor is typically a metal halide, which may be provided by evaporating a liquid metal halide, subliming a solid metal halide, or by contacting a pure metal with a halogen gas. A group IV halide deposition control agent is used to provide selective deposition on semiconductive regions of the substrate relative to dielectric regions. The semiconductive semiconductor-metal alloy layers may be doped, for example with boron, phosphorus, and/or arsenic. The precursors may be provided through a showerhead or through a side entry point, and an exhaust system coupled to the chamber may be separately heated to manage condensation of exhaust components.

An unusual copper(I) halide-based metal-organic framework with a cationic framework exhibiting the release/adsorption of iodine, ion-exchange and luminescent properties.

Abstract: A copper(I) halide-based compound with a formula of [Cu4I3(DABCO)2]I3 (DABCO = N,N′-dimethyl-1,4-diazabicyclo[2.2.2]octane) has been prepared by solvothermal reactions. This compound has been characterized by single-crystal X-ray diffraction, elemental analysis, IR, TG, XPS and powder X-ray diffractions. Structure analyses reveal that this compound is constructed by unprecedented cationic cluster [Cu8I6]2+ and organic ligand DABCO and the channels of this compound are occupied by I2 and I−. The guest I2 and I− can move freely in and out of the host-framework. UV/vis spectra confirm that the I2 molecules in the channels can release into some organic solvents and IR spectra confirm the I− was exchanged by SCN−. In addition, the luminescent properties of this compound in the solid state have also been investigated.

Deposition of films containing alkaline earth metals

Abstract: Described are methods of depositing a metal film by chemical reaction on a substrate. The method comprises: exposing the substrate to flows of a first reactant gas comprising a group 2 metal and a second reactant gas comprising a halide to form a first layer containing a metal halide on the substrate; exposing the substrate to a third reactant gas comprising an oxidant to form a second layer containing a metal peroxide or metal hydroxide on the substrate during; exposing the substrate to heat or a plasma to convert the metal peroxide or metal hydroxide to metal oxide. The method may be repeated to form the metal oxide film absent any metal carbonate impurity.

Correlation between 13C chemical shifts and the halogen bonding environment in a series of solid para-diiodotetrafluorobenzene complexes

Abstract: The co-crystallization of para-diiodotetrafluorobenzene (p-DITFB) with ammonium and phosphonium halide (Cl− and Br−) salts afforded four new compounds, [(n-Bu4PCl)(p-DITFB)] (2), [(n-Bu4NBr)(p-DITFB)] (3), [(n-Bu4PBr)(p-DITFB)] (4), and [(EtPh3PBr)2(p-DITFB)] (5), that exhibit moderately strong halogen bonding interactions. They have been characterized by single-crystal X-ray diffraction and 13C solid-state nuclear magnetic resonance (SSNMR) spectroscopy in magnetic fields of 9.4 and 21.1 T. The X-ray crystallography shows that in 2, 3, and 4, the halide is ditopic and forms long polymeric zigzag chains, whereas the bromide in 5 forms a dianionic species when involved in halogen bonding interactions. The NMR data, when combined with zeroth-order regular approximation density functional theory (ZORA–DFT) calculations, provide insight into the relationship between the strength of the halogen bond and the 13C isotropic chemical shift. When the carbon–iodine bond length increases, the 13C chemical shift also increases. Further insights into the relationship between halogen bonding and the 13C chemical shifts are obtained through additional systematic ZORA–DFT calculations as a function of the halogen bonding environment.

Potassium strontium iodide: A new high light yield scintillator with 2.4% energy resolution

Abstract: A new ternary metal halide scintillator, potassium strontium iodide, activated with divalent europium (KSr 2 I 5 :Eu) has been discovered. This material has a monoclinic crystal structure with a density of 4.39 g/cm3. Differential scanning calorimetry indicates a congruent melting point of 471°C and suggests that this compound has no solid-solid phase transitions. As is the case with most metal halides, the material is hygroscopic, and it has some internal radioactivity due to the presence of 40K. Single crystals of 13 and 25 mm diameter of KSr 2 I 5 doped with 4% Eu2+ were grown in evacuated quartz ampoules via the Bridgman technique. X-ray excited emission consisted of a single peak at ∼452 nm due to the 5d-4f transition in Eu2+. The measured light yield is ∼94,000 photons/MeV with an energy resolution of 2.4% at 662 keV.

Semiclathrate Hydrate Phase Equilibrium for CO2/CH4 Gas Mixtures in the Presence of Tetrabutylammonium Halide (Bromide, Chloride, or Fluoride)

Abstract: In this paper, hydrate phase equilibrium data for the CO2/CH4 + water system, CO2/CH4 + tetrabutylammonium bromide (TBAB) + water system, CO2/CH4 + tetrabutylammonium chloride (TBAC) + water system, and CO2/CH4 + tetrabutylammonium fluoride (TBAF) + water system were measured at temperatures from 280.2 K to 291.3 K and pressures from 0.61 MPa to 9.45 MPa with the 2.93·10–3 mole fraction of tetrabutylammonium halide. The equilibrium hydrate formation conditions were measured by an isochoric pressure-search method. The mole fractions of the mixture gas used in this work were 0.33 CO2 and 0.67 CH4. The experimental data for the CH4 + water system were contrasted with the published equilibrium data in the literature. Both have a good consistency, which demonstrates that the experimental method and the apparatus used in this paper are feasible and reliable. The experiment results show that the hydrate stable region was enlarged by adding TBAB, TBAC, or TBAF. Among the three additives, TBAF is the best and the ...

On the Effects of Temperature, Pressure, and Dissolved Salts on the Hydrogen-Bond Network of Water

Abstract: We study the structure of water through molecular dynamics, specifically the compression/expansion of the hydrogen-bond (H-bond) network, with temperature and pressure, and in salt solutions of alkali chlorides and sodium halides, and relate the observed local spatial perturbations with the tetrahedrality and the average number and lifetime of water H-bonds. The effect of transient H-bonds and transient broken H-bonds on H-bond lifetimes is further investigated, and results are compared with depolarized Rayleigh scattering lifetimes for neat water. A significant electrostriction is observed in the first hydration shell of Li+ and F–, while larger ions cause a small expansion of the H-bond network of water instead. However, both alkali cations and halide anions induce a minor contraction of the H-bond network in the second hydration shell. Further, water in the second hydration shell of Li+, Na+, and K+ is less tetrahedral than neat water, resembling water at high pressures, while the H-bond network in the...

Deposition of n-metal films comprising aluminum alloys

Abstract: Provided are methods of depositing films comprising alloys of aluminum, which may be suitable as N-metal films. Certain methods comprise exposing a substrate surface to a metal halide precursor comprising a metal halide selected from TiCl4, TaCl5 and HfCl4 to provide a metal halide at the substrate surface; purging metal halide; exposing the substrate surface to an alkyl aluminum precursor comprising one or more of dimethyaluminum hydride, diethylhydridoaluminum, methyldihydroaluminum, and an alkyl aluminum hydrides of the formula [(CxHy)3-aAlHa]n, wherein x has a value of 1 to 3, y has a value of 2x+2, a has a value of 1 to 2, and n has a value of 1 to 4; and exposing the substrate surface to an alane-containing precursor comprising one or more of dimethylethylamine alane, methylpyrrolidinealane, di(methylpyrolidine)alane, and trimethyl amine alane borane. Other methods comprise exposing a substrate surface to a metal precursor and trimethyl amine alane borane.