Chemical routes to GeS2 and GeSe2 nanowires

Nanowires of GeS(2) and GeSe(2) have been obtained by novel chemical routes involving the decomposition of organo-ammonium precursors containing super-tetrahedral Ge(4)S(10) and the dimeric Ge(2)Se(6) units.     

Über Glasbildung und Eigenschaften von Chalkogenidsystemen. IX. Zur Struktur der GeS/GeS2- und GeSe/GeSe2-Gläser

Glass Formation and Properties of Chalcogenide Systems. IX. On the Structure of GeS/GeS₂ and GeSe/GeSe₂ Glasses Mole volume, glass transition temperature, and coefficient of thermal expansion were measured on glasses prepared by standardized conditions. Near the composition Ge₂S₃ and Ge₂Se₃ the properties show a singularity or point of inflexion, respectively. Random models of structure are inconsistent with such a behaviour. A model of higher chemical order is proposed which can explain the observed dependence of the glass properties on composition and is in accordance with radial distribution studies.     

Single-crystal colloidal nanosheets of GeS and GeSe

Narrow-band-gap IV-VI semiconductors offer promising optoelectronic properties for integration as light-absorbing components in field-effect transistors, photodetectors, and photovoltaic devices. Importantly, colloidal nanostructures of these materials have the potential to substantially decrease the fabrication cost of solar cells because of their ability to be solution-processed. While colloidal nanomaterials formed from IV-VI lead chalcogenides such as PbS and PbSe have been extensively investigated, those of the layered semiconductors SnS, SnSe, GeS, and GeSe have only recently been considered. In particular, there have been very few studies of the germanium chalcogenides, which have band-gap energies that overlap well with the solar spectrum. Here we report the first synthesis of colloidal GeS and GeSe nanostructures obtained by heating GeI(4), hexamethyldisilazane, oleylamine, oleic acid, and dodecanethiol or trioctylphosphine selenide to 320 °C for 24 h. These materials, which were characterized by TEM, SAED, SEM, AFM, XRD, diffuse reflectance spectroscopy, and I-V conductivity measurements, preferentially adopt a two-dimensional single-crystal nanosheet morphology that produces fully [100]-oriented films upon drop-casting. Optical measurements indicated indirect band gaps of 1.58 and 1.14 eV for GeS and GeSe, respectively, and electrical measurements showed that drop-cast films of GeSe exhibit p-type conductivity.     

Crystal structure refinement of manganese thiogermanate Mn2GeS4

The crystal structure of Mn₂GeS₄ was solved by X-ray diffraction, on a single crystal. It has the olivine type, orthorhombic Pnma, with a = 12.776, b = 7.441, c = 6.033Å; R = 0.038 for 956 independent reflections.     

Lewis base mediated autoionization of GeCl2 and SnCl2

Cationic and anionic species of heavier low-valent group 14 elements are intriguing targets in main group chemistry due to their synthetic potential and industrial applications. In the present study, we describe the synthesis of cationic (MCl(+)) and anionic (MCl(3)(-)) species of heavier low-valent group 14 elements of germanium(II) and tin(II) by using the substituted Schiff base 2,6-diacetylpyridinebis(2,6-diisopropylanil) as Lewis base (LB). Treatment of LB with 2 equiv of GeCl(2)·dioxane and SnCl(2) in toluene gives compounds [(LB)Ge(II)Cl](+)[Ge(II)Cl(3)](-) (1) and [(LB)Sn(II)Cl](+)[Sn(II)Cl(3)](-) (2), respectively, which possess each a low-valent cation and an anion. Compounds 1 and 2 are well characterized with various spectroscopic methods and single crystal X-ray structural analysis.     

The reaction of GeCl4 with primary and secondary phosphines

Reaction of GeCl4 and CyPH2 leads to a range of products from which crystals of [CyPH3]+[GeCl3]- have been obtained. The major intermediate in this reaction, Cy(H)PGeCl3, can be obtained as the dominant product only when an excess of GeCl4 is used in the preparation. Similarly, crystals of [Ph2PH2]+[GeCl3]- have been obtained from reaction of Ph2PH and GeCl4(1 : 1). The structures of both primary and secondary phosphonium cations are reported. Aerosol-assisted and low-pressure chemical vapour deposition experiments using Cy(H)PGeCl3 as precursor lead to the deposition of thin films containing both germanium and phosphorus, contaminated with large amounts of oxygen. GeP has been identified as components of the film from bandgap measurements.     

Die Stabilität von gasförmigem GeS2

Stability of Gaseous GeS₂ For the reaction the ΔH°(298) = 33 kcal (138kJ) has been determined. This value has been obtained from chemical transport reactions as well as from mass spectrometric und thermogravimetric observations.     

Dehydrogenation of Ethanol Over Cu/ZnO Catalysts Prepared from Various Coprecipitated Precursors

For the title reaction, Cu/ZnO catalysts prepared from aurichalcite were more active than those prepared from other precursors. Selectivity to ethyl acetate over Cu/ZnO was much higher than that over Cu/SiO₂ This revised version was published online in June 2006 with corrections to the Cover Date.     

CO2 Reforming of CH4 over Nickel and Cobalt Catalysts Prepared from La—Based Perovskite Precursors

Four perovskite-type complex oxides (LaNiO3, La2NiO4, LaCoO3 and La2CoO4) were successfully prepared using two sol-gel methods, the Pechini method (PC) and the citric acid complexing method (CC). The catalysts were characterized by XRD and TPR. After reduction, the activity of the catalysts in the CO2 reforming of methane was tested. Ni-based catalysts from La2NiO4 precursors were the most active and stable catalyst after calcination above 850 癈, which gave a methane conversion of 0.025 mmol/(g-s) for those prepared by the PC method and 0.020 mmol/(g-s) by the CC method. It was proposed that the well-defined structure and lower reducibility is responsible for the unusual catalytic behavior observed over the pre-reduced La2NiO4 catalyst.     

Synthesis of BaZrS3 and BaHfS3 Chalcogenide Perovskite Films Using Single-Phase Molecular Precursors at Moderate Temperatures

Chalcogenide perovskites have garnered interest for applications in semiconductor devices due to their excellent predicted optoelectronic properties and stability. However, high synthesis temperatures have historically made these materials incompatible with the creation of photovoltaic devices. Here, we demonstrate the solution processed synthesis of luminescent BaZrS₃ and BaHfS₃ chalcogenide perovskite films using single-phase molecular precursors at sulfurization temperatures of 575 °C and sulfurization times as short as one hour. These molecular precursor inks were synthesized using known carbon disulfide insertion chemistry to create Group 4 metal dithiocarbamates, and this chemistry was extended to create species, such as barium dithiocarboxylates, that have never been reported before. These findings, with added future research, have the potential to yield fully solution processed thin films of chalcogenide perovskites for various optoelectronic applications.     

Interaction between Cr2Se3 and Cu2GeSe3

The interaction along the Cu₂GeSe₃-Cr₂Se₃ join has been investigated using differential thermal and X-ray powder diffraction analyses. It has been found that the join is quasi-binary with a degenerate eutectic based on the Cu₂GeSe₃ compound. Two new quaternary compounds have been found along the join, namely, Cu₂GeCr₆Se₁₂ and the γ phase. The phase is formed at 915°C by the peritectic reaction L + β-Cr₂Se₃ = γ and has the primary crystallization region up to 9 mol % Cr₂Se₃ in the temperature range 758–915°C. The room-temperature homogeneity range of the γ phase is 65–70 mol % Cr₂Se₃. The Cu₂GeCr₆Se₁₂ compound is formed by the peritectoid reaction γ + β-Cr₂Se₃=Cu₂GeCr₆Se₁₂ at 880°C, and its homogeneity range is 73–79 mol %. The X-ray reflections of the γ phase are indexed for the tetragonal crystal system with the unit cell parameters a = 12.043 Å and c = 9.180 Å. Samples with ferromagnetic properties are found in the homogeneity regions of both compounds.     

Electrochemistry of Layered Graphitic Carbon Nitride Synthesised from Various Precursors: Searching for Catalytic Effects

Graphitic carbon nitride (g‐C₃N₄), synthesised by pyrolysis of different precursors (dicyandiamide, melamine and urea) under varying reaction conditions (air and nitrogen gas) is subjected to electrochemical studies for the elucidation of the inherent catalytic efficiency of the pristine material. Contrary to popular belief, pristine g‐C₃N₄ shows negligible, if any, enhancement in its electrochemical behaviour in this comprehensive study. Voltammetric analysis reveals g‐C₃N₄ to display similar catalytic efficiency to the unmodified glassy carbon electrode surface on which the bulk material was deposited. This highlights the non‐catalytic nature of the pristine material and challenges the feasibility of using g‐C₃N₄ as a heterogeneous catalyst to deliver numerous promised applications.     

Structure change induced by terminal sulfur in noncentrosymmetric La2Ga2GeS8 and Eu2Ga2GeS7 and nonlinear-optical responses in middle infrared

Two new noncentrosymmetric quaternary sulfides, La(2)Ga(2)GeS(8) (1) and Eu(2)Ga(2)GeS(7) (2), have been synthesized by high-temperature solid-state reactions. The structure change on going from 1 to 2 to the known Li(2)Ga(2)GeS(6) (3) nicely shows that the reduced cation charge-compensation requirement causes a decrease in the number of terminal S atoms per formula, which is a key to determining the connectivity of the GaS(4) and GeS(4) building units. Powder sample 2 exhibits a strong second-harmonic-generation (SHG) response of about 1.6 times the benchmark AgGaS(2) at 2.05 μm laser radiation, a non type I phase-matchable behavior, and a comparable transparency region. The SHG intensities of these compounds originate from the electronic transitions from S 3p states to La/Eu/Li-S, Ga-S, and Ge-S antibonding states according to Vienna ab initio simulation package studies.     

Ortho‐Chalcogenotetrelate Anions as Chelating Ligands: Syntheses and Characterization of [K6(MeOH)9][Sn2Se6][Cr(en)2(SnSe4)]2, [Na(H2O)4][Cr(en)3]2[GeS3OH]2[Cr(en)2(GeS4)], and [Ba(H2O)10][{Cr(en)}2(GeSe4)2]

Reactions of K₄[SnSe₄], Na₄[GeS₄] or Ba₂[GeSe₄] with different 1,2‐diaminoethane (= en) coordinated complexes of CrCl₃ ([Cr(en)₂Cl₂]Cl or [Cr(en)₃]Cl₃) in MeOH or aqueous solution yielded three novel compounds that contain complexes of Cr³⁺ with ortho‐chalcogenotetrelate anions [E′E₄]^4? (E′ = Ge, Sn; E = S; Se): the crystal structures of [K₆(MeOH)₉][Sn₂Se₆][Cr(en)₂(SnSe₄)]₂ ( 1 ), [Na(H₂O)₄][Cr(en)₃]₂[GeS₃OH]₂[Cr(en)₂(GeS₄)] ( 2 ), and [Ba(H₂O)₁₀][{Cr(en)}₂(GeSe₄)₂] ( 4 ) have been determined by means of single crystal X‐ray diffraction ( 1 : triclinic space group ; lattice dimensions at 203 K: a = 1175.7(2), b = 1315.3(3), c = 1326.7(3) pm, α = 61.99(3)°, β = 64.05(3)°, γ = 83.57(3)°, V = 1617.4(6)·10⁶ pm³; R₁ [I > 2σ(I)] = 0.0788; wR₂ = 0.1306; 2 : monoclinic space group C2/c; lattice dimensions at 203 K: a = 2445.3(5), b = 1442.5(3), c = 1579.3(3) pm, β = 94.61(3)°, V = 5552.9(19)·10⁶ pm³; R₁ [I > 2σ(I)] = 0.0801; wR₂ = 0.2046; 4 : triclinic space group ; lattice dimension at 203 K: a = 1198.4(2), b = 1236.8(3), c = 1297.5(3) pm, α = 65.69(3)°, β = 63.35(3)°, γ = 81.21(3)°, V = 1565.2(5)·10⁶ pm³; R₁ [I > 2σ(I)] = 0.0732; wR₂ = 0.1855). 1 and 2 show the yet unprecedented complexation of transition metal ions by non‐bridging, single chalcogenotetrelate ligands to produce dinuclear, heterobimetallic complexes. Compound 2 contains the first structurally characterized complex with an ortho‐thiogermanate ligand. The formation of these compounds, and of a by‐product of 2 , [Cr(en)₃][GeS₃OH]·6H₂O ( 3 : monoclinic space group C2/c; lattice dimensions at 203 K: a = 2396.8(5), b = 1463.4(3), c = 1740.1(4) pm, β = 132.99(3)°, V = 4463.8(15)·10⁶ pm³; R₁ [I > 2σ(I)] = 0.0462; wR₂ = 0.1058), provides some insight in fundamental differences between the reaction behavior of [SnE₄]^4? anions one the one hand and [GeE₄]^4? anions on the other hand. The crucial role of the counterion charge becomes evident when comparing the structure motifs of the ternary anions in 1 and 2 with that observed in the Ba²⁺ compound 4 .     

Simple Stereocontrolled Synthesis of Methyl 2-Deoxy-d-erythro-hexopyranosid-4-uloses,Thromboxane B2 (TXB2) Precursors,from d-Galactose

Abstract

The stereospecific synthesis of methyl 3-O-benzoyl-6-O-(tert-butyldiphenylsilyl)-2-deoxy-α-d-erythro-hexopyranosid-4-ulose (5) - a Thromboxane B₂ (TXB₂) precursor -starting from D-galactose is described. Facile and established methods including selective benzoylation, oxidation-elimination and a stereocontrolled hydrogenation (Pd/charcoal) were employed effectively.     

Raman scattering in GeS2 glass and its crystalline polymorphs compared

Raman spectrum of glassy GeS₂ and low-resolution ones of polycrystalline α- and β-GeS₂ were studied. It was shown that the medium range structure of glassy GeS₂ is similar to the three-dimensional structure of β-GeS₂. Our conclusion of similarity of medium range order of glassy GeS₂ and β-GeS₂ was also confirmed by detection of β-GeS₂ microcrystals grown from glassy GeS₂ at annealing temperature sufficiently below glass transition temperature.     

2-Amino-4-dimethylamino-1-thia-3-azabutadienes as Precursors of Thiazoles

The reaction of 2-amino-4-dimethylamino-1-thia-3-azabutadienes 1 with f -bromoketones gave rise to 2-aminothiazoles 2 together with 2-( N , N -dimethylaminomethylenamino)thiazoles 3 . Competitive mechanisms are described. Furthermore, reaction of diene 1a with methyl f -bromoacetate or hydroxylamine- O -sulfonic acid yielded respectively 2-( N , N -dimethylaminomethylenamino)thiazolin-4-one 4 and 5-amino-1,2,4-thiadiazole 5 .     

4-(2-Hydroxyaryl)-1,2,3-selenadiazoles as Precursors of Benzofuran-2-selenolates

The reaction of selenium dioxide with o-hydroxyacetophenone semicarbazones gives 4-(2-hydroxyaryl)-1,2,3-selenadiazoles which undergo ready decomposition by the action of potassium carbonate to form benzofuran-2-selenolates. The latter can be alkylated with methyl iodide and benzyl chloride and arylated with 2,4-dinitrochlorobenzene. Intermediate formation of 2-(o-hydroxyphenyl)ethyneselenolate during decomposition of 1,2,3-selenadiazoles was proved by the isolation of methyl o-methoxyphenylethynyl selenide when the substrate was treated with potassium carbonate in the presence of methyl iodide.