Synthesis and structure of a gallate of strontium with Sr–C–Ga three-center two-electron bonds

The addition reaction of strontium bis[bis(trimethylsilyl)amide] with triethylgallane yields quantitatively strontium bis[triethyl-bis(trimethylsilyl)aminogallate] (1). The strontium cation shows the unusual low coordination number of four to two nitrogen and two carbon atoms. Sr–C bond lengths with a mean value of 282 pm are observed with the Sr–C–Ga three-center two-electron bonds. Due to the mainly ionic character of this compound a fast exchange of the bridging and terminal ethyl groups is observed on the NMR time scale.     

Electrochemical reactivity of nanocomposite ZnO–Se for lithium-ion batteries

Nanocomposite ZnO–Se thin film has been successfully fabricated by pulsed laser deposition method. The electrochemical behavior is investigated by galvanostatic cycling and cyclic voltammetry. The reversible specific capacity of ZnO–Se/Li cells cycled between 0.01 and 3.5 V is found to be 505 mAh g^?1 with good capacity retention. Nanocomposite ZnO–Se thin film electrode exhibits much better electrochemical performance than pure ZnO. The reversible oxidation/reduction reaction of ZnO and selenidation/reduction reaction of ZnSe are revealed in the electrochemical reaction mechanism of nanocomposite ZnO–Se with lithium.     

Analysis of the Composition of CuI–As2Se3 and CuI–PbI2–As2Se3 Chalcogenide Films by X-ray Fluorescence Spectroscopy

The chalcogenide films As₂Se₃, CuI–As₂Se₃, and CuI–PbI₂–As₂Se₃ are prepared through chemical deposition from an organic solvent and investigated by X-ray fluorescence spectroscopy. The contents of the main components of the chalcogenide films are compared by analyzing the intensity ratios for the AsK , SeK , and CuK lines. It is found that the content of the main components (As, Se, and Cu) is virtually the same in binary chalcogenide, pseudobinary, and multicomponent chalcogenide systems, no matter what the technique used for preparing the materials (films deposited from solutions of chalcogenide glasses in n-butylamine and bulk glasses). This result is consistent with a model of dissolution of vitreous semiconductors in organic bases (amine) according to which the fundamental properties of bulk glasses remain unchanged upon formation of the films. The experimental data indicate an analogy between the properties of the multicomponent chalcogenide glasses CuI–As₂Se₃ and CuI–PbI₂–As₂Se₃ and the chalcogenide glass–based films.     

Development of a composite substrate peel test to assess moisture sensitivity of aggregate–bitumen bonds

This paper presents the development of a suitable procedure to prepare peel test specimens using coarse aggregates and compare the results with the established standard peel test. The newly developed composite substrate peel test (CSPT) was found to be effective in characterising the moisture sensitivity of the aggregate–bitumen bond and the results correlated well with the results from a standard peel test. The results from the CSPT and the standard peel test showed that the fracture energy after moisture damage was found to be aggregate type dependent. Limestone tends to have better resistance to moisture damage than granite when moisture adsorptions are similar. Furthermore, in terms of similar aggregates, lower moisture adsorption results in better moisture resistance. This phenomenon suggests that in a moisture susceptible asphalt mixture, the effect of aggregate may be more influential than the effect of bitumen. Strong correlations were found between the standard peel test and the CSPT in terms of moisture damage evaluation and suggest that the CSPT maybe a more practical procedure to test the aggregate–bitumen bond for actual aggregates used in asphalt mixtures.     

Electrical Switching in Cu–As–Se Glasses

Electrical switching in Cu_xAs₄₀Se_60−x glasses has been studied over a wide composition range for 0≤x≤32. The glasses with lower Cu concentrations (x<15) do not exhibit switching, whereas glasses in the range 15≤x≤25 show a threshold type switching. The glasses in the range 26≤x≤29 exhibited an unusual switching from low-resistance to high-resistance state. For x≥30, the glasses are found to show a memory switching. The thermally crystallized samples indicate that the structural network is characterized by Cu₃AsSe₄ and As₂Se₃ for x<15 and by Cu₃AsSe₄ and Cu₂As₃ for x≥25. The composition range 15≤x≤20 is characterized only by Cu₃AsSe₄ structural units. The samples cooled from their melt show only the ternary Cu₃AsSe₄ for x≤20. For x>20, precipitates of “As” have also been observed along with Cu₃AsSe₄ and Cu₂As₃ phases. The present studies provided a unique way to understand the electrical switching exhibited by chalcogenide glasses based on the thermal model and the filament formation.     

A novel solid–liquid route for the preparation of Cu3Se2 and Ag2Se nanocrystals

Cu₃Se₂ and Ag₂Se nanocrystals have been synthesized with Se as the precursor in aqueous solutions under photo-irradiation at room temperature. The obtained products were analyzed through X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results showed that the tetragonal phase of Cu₃Se₂ with nearly spherical grains and the orthorhombic phase of Ag₂Se with nanoscale dendrite were formed. The experiments also confirmed that photo-irradiation and Na₂SO₃ played important roles in the formation of Cu₃Se₂ and Ag₂Se nanocrystals. The formation mechanism of Cu₃Se₂ and Ag₂Se nanocrystals was investigated in detail.     

A rare 2D coordination polymer of graphite-like structure extended by infinite silver–oxygen–silver bonds

The reaction of AgNO₃ and H₃btb (H₃btb = 1,2,3-benzenetricarboxylic acid) leads to the isolation of {[Ag(μ₂-H₂O)(μ₂-H₂btb)]}_n · 1.5nH₂O (1), which crystallizes in the orthorhombic space group Fddd with a = 11.436(2) Å, b = 6.876(1) Å, c = 58.837(1) Å, V = 4626.5(2) Å³, Z = 32. Silver ions are connected by both strong Ag?Ag interaction and μ₂-H₂O bridges to form hexagonal Ag₆ subunits, and are further assembled into a high ordered 2D grid, presenting an interesting graphite-like 6³ net. Both the fluorescence and the crystal transformation after dehydration are studied.     

Surface damage and threshold determination of Ge–As–Se glasses in femtosecond pulsed laser micromachining

Ge–As–Se chalcogenide glasses were prepared and the surface damage characteristics under femtosecond laser irradiation were experimentally investigated. Femtosecond laser beams with different power intensities, focusing depths, pulse repetition rates, and pulse numbers were employed to determine the damage thresholds of the samples. The surface morphologies and feature sizes of the damage craters were studied with regard to laser energy density to evaluate the damage circumstances of the glasses. The generation of the surface damage was also recorded by using different numbers of pulses. Results showed that the damage area increased monotonically with the laser power at low energy density and tended to saturation when reaching a critical value. According to the linear circumstances of laser energy density on the damage crater area, the average damage thresholds of the Ge–As–Se glasses with different repetition rates and pulse numbers were obtained. Results showed that the damage threshold decreased with the increase in pulse repetition rate and number of pulse.     

Highly selective reductive cleavage of aromatic carbon–oxygen bonds catalyzed by a cobalt compound

A cobalt catalyst has been demonstrated, for the first time, to be effective for the reductive cleavage of inert aromatic CO bonds with high selectivity. Compared with previous Ni catalysts, the cobalt catalyst reported here is more commercially available and air-stable.     

Chlorinating cleavage of silicon–naphthyl bonds of polycarbosilane,and introduction of poly(ethylene glycol) graft copolymer micelles

A new series of polycarbosilanes [(PhCH₂)SiCH₃Cl, Poly B] was designed by chlorinating cleavage reaction of silicon–naphthyl in polycarbosilane. The ¹H spectra of poly B revealed that the SiCH₂ and the SiCH₃ protons peak were up-field shifted compared with the type [(PhCH₂)SiCH₃Np, Poly A] polycarbosilane. Grafted polycarbosilane was synthesized with poly ethylene glycol (PEG) by nucleophilic substitution of the chloride substituents on the polycarbosilane. The aggregation behaviors of graft copolymers were investigated by dynamic light scattering and fluorescence at 25 °C in aqueous solutions of different polyethylene glycol (PEG) substituent.     

微量氧化物对Se基硫系玻璃中H–Se杂质的影响

传统硫系玻璃必须在完全隔氧的环境下进行熔制,但是微量氧化物对硫系玻璃的具体性能影响仍是一个问题.为了探究微量氧化物对As–Se玻璃中Se–H杂质的影响,使用SeO2药品对Se原料进行提纯,通过主动蒸馏法制备了多组玻璃样品,对比研究其在Ge引入后形成的弱还原条件对SeO2发挥作用的效率变化情况.光谱特性和相关数据表明:2...     

Determination of the Fluctuation Free Volume Fraction for Glasses in the As–S(Se) Systems

The fraction f _g of fluctuation free volume frozen at the glass transition temperature is determined from the temperature dependence of the viscosity in terms of the Vogel–Fulcher–Tammann equation and the formula T _g = f _gln(1/f _g). The fluctuation free volume fractions obtained using these two procedures for glasses in the As–S(Se) systems are in quite reasonable agreement. It is demonstrated that the difference in the ratios between the fraction of fluctuation free volume and the lattice Grüneisen parameter for chalcogenide and oxygen-containing glasses is associated with the specific structure of the network of chalcogenide glasses. It is found that the dependence of the fluctuation free volume fraction on the mean coordination number Z _m, which characterizes the degree of connectivity of the network in noncrystalline materials, exhibits nonmonotonic behavior.     

The optical spectra characterization of Cr2+:ZnSe polycrystalline synthesized by direct reaction of Zn–Cr alloy and element Se

Cr²⁺:ZnSe materials have attracted much attention as candidates for mid-infrared laser source either in the form of polycrystalline powders, or bulk ceramics, single crystals and nano-materials. In this work, a novel method for synthesizing Cr²⁺:ZnSe polycrystalline by direct reaction of Zn–Cr alloy and element Se (DRAE) was proposed. The zinc alloy containing 0.1 at% Cr was prepared by dissolving Cr in zinc liquid in a closed quartz ampoule. X-ray diffraction (XRD) results showed that the synthesized Cr²⁺:ZnSe polycrystalline was with a Zinc-blend structure. X-ray photoelectron spectroscopy (XPS) spectra showed that there was no un-reacted element of Zn, or Se. Cr²⁺ ions successfully and uniformly doped into ZnSe crystal lattice, which is confirmed by the diffuse reflectance spectrum, Raman spectrum and mid-infrared photoluminescence spectra. Furthermore, the sample showed excellent mid-infrared properties without luminescence quenching in the region 1800–3000 nm, and the decay-time was about 5 μs. The as-synthesized Cr²⁺:ZnSe polycrystalline meets the requirement for the preparation of mid-infrared ceramic or single crystals. These results indicate that the novel strategy of DRAE is valid for the synthesis of other transition metal doped ZnSe materials.     

Low gallium-content,dysprosium III-doped,Ge–As–Ga–Se chalcogenide glasses for active mid-infrared fiber optics

A systematic investigation is presented, for the first time, of a 1000 ppmw (parts per million, by weight) Dy³⁺-doped Ge–As–Ga–Se chalcogenide glass series, with a fixed low Ga content of 1 atomic% (at. %), suitable for active mid-infrared fiber optics. Seven glasses constitute the series, which have increasing average coordination number from 2.49 to 2.61, in steps of 0.02, with the GeSe₂, As₂Se₃, and Ga₂Se₃ stoichiometries kept. Glass formation is confirmed using X-ray diffraction and differential scanning calorimetry. Fourier transform infrared spectroscopy is reported for the series. Parallel plate viscometry enables prediction of fiber-drawing temperatures and, with differential thermal analysis, determines the potential for fiber fabrication. X-ray diffraction of samples after parallel-plate viscometry shows that Ge₂₅As₉Ga₁Se₆₅ (at. %) alone, in the glass-series, devitrifies to form the single-crystalline phase: monoclinic-GeSe₂; scanning electron microscope imaging suggests that this phase is both surface and bulk grown. Overall, the recommended host glass at. % compositions for doping with rare-earth ions and drawing to active mid-infrared fiber are: Ge_17.5As₁₈Ga₁Se_63.5, Ge₁₅As₂₁Ga₁Se₆₃, and Ge_12.5As₂₄Ga₁Se_62.5.     

Chemisorption of halogen on carbons—I Stepwise chlorination and exchange of C-CI with C-H bonds

Stepwise chlorination at 773 K of carbons and the resulting amounts of HC1 released can be interpreted by assuming that saturation of olefinic bonds by Cl₂ occurs first. This is followed by exchange with the chemibound hydrogen and lastly by slight dehydrogenation of the adsorbent, yielding HCl and olefinic bonds. High-temperature chlorination-hydrogenation cycles may be performed many times to a depth of 3.4 meq/g without appreciable weight loss or change in pore structure of an activated carbon.     

Site-Selective Pyridination of Benzylic and Allylic C−H bonds via Radical-Radical Cross-Coupling

Herein, we report a modular photocatalytic platform for the site-selective pyridination of saturated hydrocarbon compounds employing organic photoredox catalysis to forge new carbon-carbon bonds. The site-selective C−H pyridination could couple benzylic/allylic C−H bonds with pyridylphosphonium salts, which installed directly and regioselectively from C−H heteroarenes through a radical-radical cross coupling mechanism. This synthetic methodology could tolerate a variety of functional groups, complex heteroarenes, even late-stage functionalization of pharmaceuticals selectively.     

A vibrational study of the activation sequence of C–H and C–C bonds of isobutene and 1-butene on Mo(110) and (4 × 4)-C/Mo(110) surfaces

The thermal decomposition pathways of isobutene and 1-butene on both Mo(110) and 4 × 4-C/Mo(110) surfaces have been studied using high-resolution electron energy loss spectroscopy (HREELS) in order to highlight the substantially different activities of these two surfaces towards the cleavage of C–H and C–C bonds. On clean Mo(110), the CH₂ group of isobutene decomposes upon heating to 150 K, producing either a /-bonded isobutenylidene [(CH₃)₂CCH] species or a 1,1-di-/-bonded isobutenyl [(CH₃)₂CC] species. Upon further heating, extensive C–H bond scission occurs to form hydrocarbon fragments which do not contain CH₃ or CH₂ groups, but appear to have largely intact carbon skeletons. By contrast, isobutene is molecularly adsorbed on the carbide-modified surface at 150 K. Further heating produces isobutylidyne [(CH₃)₂HCC] by 300 K, which subsequently decomposes via C–C bond scission to generate surface methyl groups. The different activation sequence of the C–H and C–C bonds of isobutene on clean and carbide-modified Mo(110) surfaces is also qualitatively confirmed by comparative studies of 1-butene on the two surfaces.     

Effect of pH on the Catalytic Properties of Mo–V–Te–P–O Catalysts for Selective Oxidation of Isobutane

Mo–V–Te–P mixed oxide catalysts, prepared by a dry-up method at various pHs (in the range of about 1.0–9.0), have been tested in the partial oxidation of isobutane. The best catalytic performance was achieved over a catalyst prepared at a pH about 7.0. In this case, high selectivity to methacrolein (37.0%) at an isobutane conversion of 12.7% has been obtained at 380 °C. The surface V⁴⁺/V⁵⁺ ratios of the calcined samples were strongly influenced by the pH in the synthesized solution, which is one of the key factors in the catalytic performance for selective oxidation of isobutane.     

Three Ag(I)–cyanide coordination polymers with metal bonds tuned by N-heterocyclic ligands

Hydrothermal reactions of AgNO₃, K₃[Fe(CN)₆] with N-heterocyclic ligands afforded three novel Ag(I)–cyanide coordination polymers, [Ag₂(CN)₂(tpt)]_n (1), {[Ag(CN)(bpe)_0.5][Ag(CN)]}_n (2) and [Ag(CN)(btmb)_0.5]_n (3) (tpt = 2,4,6-tris(4-pyridyl)-1,3,5-triazine, bpe = 1,2-bis(4-pyridyl)ethane, btmb = 1,2-bis(1,2,4-triazol-1-ylmethyl)benzene). In complex 1, two Ag(CN) linear chains are bridged by bidentate tpt ligand to form a ladder-like structure, which are further connected by AgAg metal bond to generate a 2D polymeric network. Complex 2 is an interesting 3D supramolecular architecture assembled by 2D [Ag¹(CN)(bpe)_0.5]_n network and linear [Ag²(CN)]_n chain combined by strong AgAg metal bond. Complex 3 is a 1D ladder-like double-chain polymer constructed from Ag–cyanide linear chains and btmb spacer, which is further extended to a 2D supramolecular network by Ag–Ag weak interaction. The Ag–Ag metal interactions play important roles in the construction of three coordination polymers. Complexes 1 and 2 are respectively thermally stable at 300 and 180 °C. Complexes 1 and 3 emit strong blue luminescence.