Search results for "TUNGSTEN"
showing 10 items of 372 documents
Sodium nitrate and tungsten as matrix modifiers for the determination of arsenic in shotgun pellets by electrothermal atomic absorption spectrometry
2001
A method for the determination of arsenic in a complicated sample matrix by Zeeman effect electrothermal atomic absorption spectrometry using tungsten and sodium nitrate as matrix modifiers was developed. The determination of arsenic in SRM C2416 (Bullet Lead) and SRM 2710 (Montana Soil) by ETAAS using a mixture of palladium and magnesium nitrate as a matrix modifier failed to obtain the certified concentrations at the 95% level of confidence using the t-test. Both tungsten and sodium nitrate as matrix modifiers stabilized arsenic so that the certified concentrations of the SRMs were determined with high accuracy and precision (RSD 0.999), with low detection and quantification limits, wer…
High yield synthesis of trinuclear [M3S4X3(diphos)3]+ (M=Mo, W; X=Cl, Br and diphos=dmpe, dppe) molecular clusters from solid state materials. Synthe…
2001
The excision of polymeric {M 3 S 7 X 4 } x (M=Mo, W; X=Cl, Br) cluster phases with diphosphines (dmpe, dppe) in acetonitrile affords a one step general synthetic route for the preparation of trinuclear molecular clusters with formula [M 3 S 4 X 3 (diphos) 3 ] + (M=Mo, W; X=Cl, Br and diphos=dmpe, dppe) in high yields. Following this strategy, the cluster cations [Mo 3 S 4 Br 3 (dmpe) 3 ] + and [W 3 S 4 Br 3 (dppe) 3 ] + have been prepared for the first time. This last tungsten cluster has proved to be a useful synthon for the synthesis of the hydride derivative [W 3 S 4 H 3 (dppe) 3 ] + in moderate yields. The crystal structure of [W 3 S 4 H 3 (dppe) 3 ](BPh 4 ) consists of a equilateral tu…
Synthesis, characterization, and hierarchical organization of tungsten oxide nanorods: spreading driven by Marangoni flow.
2009
Tungsten oxide nanorods were synthesized by a soft chemistry approach using tungsten alkoxide and trioctyl amine and oleic acid as the surfactants. The optical properties of the nanorods were studied. The nanorods were found to be soluble in a wide range of solvents like chloroform, cyclohexane, and so on. Upon solvent evaporation, the nanorods formed hierarchically organized solid state structures. Depending on the solvent used, the nanorods organized in different mesostructures. Moreover, the organization of the nanorods from mixtures of polar and nonpolar solvents was studied. Here, the Marangoni effect resulting from differences in the surface tensions of the two solvents was found to p…
Dalton communication. Crystal structure and oxo-transfer properties of [NH4]2[WVIO2{O2CC(S)Ph2}2]
1994
The complex [NH4]2[WVIO2{O2CC(S)Ph2}2] is the first example of a non-dithiolene tungsten complex capable of oxidising benzoin to benzil in methanol; the reduced complex product formed, presumably a monomeric WVIO species, was reoxidised with nitrate ions, regenerating the starting WVIO2 complex which then acts as a true homogeneous catalyst.
Modes of complexation of non-substituted and substituted tetraazamacrocycles with Group 6 metal carbonyls. X-ray structure of [(permethylcyclam)Mo(CO…
1995
Abstract Reactions of complexation of tetraazamacrocycles L with Group 6 metal carbonyls [M(CO)6](M = Cr, Mo, or W) lead to [LM(CO)4], [LM(CO)3] or [LM(CO)2] entities, depending both on the size of the macrocycle and on the metal M. The structure of one representative complex [(permethylcyclam)Mo(CO)4] has been determined by X-ray diffraction (permethylcyclam: 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane).
Aminobis(phenolate)s of imidomolybdenum(VI) and -tungsten(VI)
2009
Abstract The reactions of trans-[MoO(ONOMe)Cl2] 1 (ONOMe = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) dianion) and trans-[MoO(ONOtBu)Cl2] 2 (ONOtBu = methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate) dianion) with PhNCO afforded new imido molybdenum complexes trans-[Mo(NPh)(ONOMe)Cl2] 3 and trans-[Mo(NPh)(ONOtBu)Cl2] 4, respectively. As analogous oxotungsten starting materials did not show similar reactivity, corresponding imido tungsten complexes were prepared by the reaction between [W(NPh)Cl4] with aminobis(phenol)s. These reactions yielded cis- and trans-isomers of dichloro complexes [W(NPh)(ONOMe)Cl2] 5 and [W(NPh)(ONOtBu)Cl2] 6, respectively. The molecular st…
Cluster-model density functional study of a W–Cu(100) STM junction
1999
Abstract In this article, we investigate the electronic properties of different clusters modelling a tungsten tip, the Cu(1 0 0) surface and interacting W–Cu(1 0 0) systems in STM configuration. Electronic structure calculations are carried out within the LDA approximation of the Density Functional Theory (DFT). Both integrated (densities of states) and local properties (electronic density and electrostatic potential) are considered. The study is performed for top and hollow surface sites and two different tip–sample separations.
Chelated η5-cyclopentadienyl-η-ethyl complexes of molybdenum and tungsten; molecular structure of W(η5-C5H4CH2-η-CH2)(CO)3
2000
Abstract Molybdenum and tungsten complexes M(η5-C5H4CH2-η-CH2)(CO)3 (M=Mo, W) containing the bidentate ethyl-functionalized cyclopentadienyl ligand C5H4CH2CH2 have been synthesized by the reaction of spiro[2.4]hepta-4,6-diene with M(CO)3L3 (M=Mo; L3=1,3,5-C6H3Me3; M=W; L=NCMe). Reaction of the more stable tungsten complex with C6H5ICl2 and HBF4 gave complexes of the type W(η5-C5H4CH2CH2Cl)(CO)3Cl, W(η5-C5H4CH2CH3)(CO)3Cl and W(η5-C5H4CH2CH3)(CO)3(FBF3), respectively. The crystal structure of the tungsten tricarbonyl complex W(η5-C5H4CH2-η-CH2)(CO)3 has been determined by X-ray crystal diffraction on a single crystal and shows a four-legged piano stool structure.
A simple method to fabricate high-performance nanostructured WO3 photocatalysts with adjusted morphology in the presence of complexing agents
2017
[EN] The rich and complex chemistry of tungsten was employed to synthesize innovative WO3 nanoplatelets/nanosheets by simple anodization in acidic electrolytes containing different concentrations of complexing agents or ligands, namely F- and H2O2. The morphological and photoelectrochemical properties of these nanostructures were characterized. The best of these nanostructures generated stable photocurrent densities of ca. 1.8 mA cm(-2) at relatively low bias potentials (for WO3) of 0.7 V-Ag/AgCl under simulated solar irradiation, which can be attributed to a very high active surface area. This work demonstrates that the morphology and dimensions of these nanostructures, as well as their ph…
Tetragonal tungsten bronze compounds: relaxor versus mixed ferroelectric-dipole glass behavior.
2011
We demonstrate that recent experimental data (E. Castel et al J.Phys. Cond. Mat. {\bf 21} (2009), 452201) on tungsten bronze compound (TBC) Ba$_2$Pr$_x$Nd$_{1-x}$FeNb$_4$O$_{15}$ can be well explained in our model predicting a crossover from ferroelectric ($x=0$) to orientational (dipole) glass ($x=1$), rather then relaxor, behavior. We show, that since a "classical" perovskite relaxor like Pb(Mn$_{1/3}$ Nb$_{2/3}$)O$_3$ is never a ferroelectric, the presence of ferroelectric hysteresis loops in TBC shows that this substance actually transits from ferroelectric to orientational glass phase with $x$ growth. To describe the above crossover theoretically, we use the simple replica-symmetric so…