Search results for "Tellurium"
showing 10 items of 135 documents
Experimental Investigations and Ab Initio Studies of Tellurium(II) Dithiolates, Te(SR)2
1999
The reaction between Te(O(i)Pr)(4) and HSR offers a new and effective route to tellurium dithiolates, Te(SR)(2). Te(S(i)Pr)(2) (1) and Te(S(t)Bu)(2) (2) are stable compounds whereas Te(SPh)(2) (3) slowly decomposes at room temperature to give Te and Ph(2)S(2). IR spectra of 1-3 and ab initio calculations (HF/3-21G(d) and MP2 with double-zeta polarization effective core potential basis set) show nu(as)(Te-S) and nu(s)(Te-S) to be around 340 and 380 cm(-)(1), respectively. UV spectra exhibit similar lambda(max) (346-348 nm) for all three compounds, with the greater extinction coefficient of 3 accounting for its different and more intense color. Analysis of the molecular orbitals of the model …
Thermal stability and reaction of chalcogen-containing metallocenic compounds with elemental chalcogens
1989
Abstract Dissymmetrical four-membered bimetallocenacycles (t-BuC 5 H 4 ) 2 M(μ-S) 2 M′-(RC 5 H 4 ) 2 (M, M′ = Zr, Hf; R = H, t-Bu) have been prepared and found to give redistribution products in solution at 190°C; identification of these products shows that the reaction involves exclusive cleavage of a metal-sulfur bond. Elemental sulfur and selenium react with chalcogen-containing complexes. The reaction is shown to involve the introduction of chalcogenic species in place of the σ-ligands of the complex to give either four-membered bimetallic complexes or catenated pentachalcogen metallocenic compounds. Some examples of insertion of sulfur and tellurium into the zirconium-methyl bond are a…
Nb 4 Te 17 I 4 , a New Pseudo One‐Dimensional Solid‐State Polytelluride
1994
The new ternary compound Nb4Te17I4 has been prepared and structurally characterized. It crystallizes in the monoclinic system, space group C2/c with unit-cell parameters a = 16.199(4), b = 8.128(2), c = 27.355(6) A, β = 110.84(2)°, Z = 4. The structure consists of infinite one-dimensional niobium/tellurium chains running parallel to the crystallographic c direction. The chains are separated by iodine atoms. Short and long metal–metal distances alternate in the sequence of three consecutive short bonds ([d ≈ 3.1 – 3.2 A) and one long (d = 4.268 A) metal–metal separation. Each Nb atom is eight-coordinate. The composition of the chain is ∞11[(Nb5+)2(Nb4+)2(Te22−)4(Te32−)3(I−)4].
Influence of gel composition in the synthesis of MoVTeNb catalysts over their catalytic performance in partial propane and propylene oxidation
2010
[EN] MoVTeNb mixed oxides catalysts have been prepared by a slurry method with different molar compositions (Mo/Te ratio from 2 to 6 and Nb/(V + Nb) ratio from 0 to 0.7) in the synthesis gel leading to different crystalline phases distribution and catalytic behaviour in the partial oxidation of both propane and propylene to acrylic acid. Chemical analysis indicates that the composition of samples before and after the heat-treatment changes, especially the Te-content, since a significant amount of Te is lost during the heat-treatment step when the amount of oxalate (from niobium oxalate) increases in the synthesis gel. Thus, the nature of the crystalline phases and the catalytic performance …
Spectroscopic Investigation of the System TeCl4/[NEt4]PF6 in Solution and the Crystal Structure of [NEt4]2[Te2Cl10].
2005
Solutions containing TeCl 4 and [NEt 4 ][PF 6 ] in CH 2 Cl 2 were investigated by means of UV/vis and NMR spectroscopy in order to study the complex chemistry of TeCl 4 with the [PF 6 ] - anion. The results show formation of [TeCl 5 ] - and strong interactions of [PF 6 ] - with a tellurium containing species, presumably [TeCl 3 ] + . The life time of the Te I V -PF 6 complex is long enough to give different signals in the 1 9 F NMR spectrum of a solution containing excess [PF 6 ] - . Even a fivefold excess of Cl - ions over [PF 6 ] - does hardly lead to a dissociation of [TeCl 3 ...PF 6 ]. Crystals of [NEt 4 ] 2 [Te 2 Cl 1 0 ] were obtained from a 4:1 solution of [NEt 4 ]PF 6 and TeCl 4 in …
ChemInform Abstract: Ta1.09Fe2.39Te4, a New Non-Stoichiometric Ternary Tantalum Telluride.
2010
Abstract Ta1.09Fe2.39Te4 was prepared by chemical transport from the elements in sealed silica tubes in a temperature gradient from 700 to 600 °C. It crystallizes in the monoclinic space group P2/m with a = 6.162(2) A , b = 7.852(3) A , c = 7.250(3) A , β = 95.32(3)° and Z = 2 . Its structure can be derived from a hexagonal close packing of tellurium atoms with tantalum and iron atoms in octahedral voids and additional iron atoms in tetrahedral voids. The structure is closely related to the structures of MM'Te2 (MNb, Ta; M′Fe, Co, Ni) and MxFeγTe2 (MNb, x = 0.89, γ = 0.93; MTa, x = 0.77, γ = 0.90).
Hydride generation atomic fluorescence spectrometric determination of ultratraces of selenium and tellurium in cow milk
2003
Abstract A sensitive procedure has been developed for selenium and tellurium determination in milk by hydride generation atomic fluorescence spectrometry (HG-AFS) after microwave-assisted sample digestion. The method provides sensitivity values of 1591 and 997 fluorescence units ng−1 ml−1 with detection limits of 0.005 and 0.015 ng ml−1 for Se and Te, respectively. The application of the developed methodology to the analysis of cow milk samples of the Spanish market evidenced the presence of concentration ranges from 11.1 to 26.0 ng ml−1 for Se, and from 1.04 to 9.7 ng ml−1 for Te having found a good comparability with data obtained after dry-ashing of samples.
Multicommutation hydride generation atomic fluorescence determination of inorganic tellurium species in milk
2005
Abstract A multicommutated flow system has been developed for hydride generation, atomic fluorescence (HG-AFS) determination of tellurate (Te VI ) and tellurite (Te IV ) in milk samples. After a batch leaching of Te by sonication at room temperature for 10 min with aqua regia, sample slurries in acidic medium were merged with sodium borohydride and HCl to obtain data on Te IV . Another portion of the acidic slurry was mixed with KBr and passed through a reaction coil introduced inside a microwave oven to reduce quantitatively Te VI to Te IV which was analyzed by HG-AFS. The detection limit was 0.57 ng g −1 in the original samples. The linear range obtained was till 4 ng ml −1 and the averag…
Speciation of selenium and tellurium in milk by hydride generation atomic fluorescence spectrometry
2004
A simple, fast and highly sensitive method has been developed for the differentiation of Se and Te into their (IV) and (VI) oxidation states in milk samples by HG-AFS. This procedure involves a previous leaching of milk slurries by sonication with aqua regia for 10 min. Se(IV) and Te(IV) were determined by analysis of the samples without a pre-reduction step; being total Se and Te determined after reduction with KBr. The method provides limit of detection values (LOD) of 0.012 and 0.023 ng ml−1 for Se(IV) and Te(IV) respectively. Average relative standard deviation values of 10.5%, 3.9%, 12% and 12.5% were found for the determination of Se(IV), Se(VI), Te(IV) and Te(VI) in milk samples cont…
Multicommutation as an environmentally friendly analytical tool in the hydride generation atomic fluorescence determination of tellurium in milk.
2003
The aim of this study is to show the advantages of the emerging multicommutation methodology based on the use of solenoid valves for Te determination in milk by hydride generation atomic fluorescence spectrometry (HG-AFS). The delivery of a series of alternating sequential insertions of small volumes of samples and reagents gives rise to new hydrodynamic processes and exciting analytical potentials by controlling the time of flow through the on/off-switched solenoid valves. This drastically reduces the reagent consumption by a factor of 4 and the generation of effluents (590 mL h(-1) instead of 750 mL h(-1) generated by the continuous-mode measurement) and also provides an improvement in th…