Tungsten Compounds Research Articles

Formation of intermetallic compounds with a high flux pulse molybdenum ion beam in steel and aluminium

Intermetallic compounds of molybdenum and tungsten implanted into H13 steel and aluminium were measured by transmission electron microscopy (TEM) and X-ray diffraction. Ions extracted from a metal vapour vacuum arc source with around 25–100 keV energy and a dose range (1–5) × 10 17 cm -2 were used for implantation. The ion fluxes were 25, 47, 68 and 320 μA cm -2. It was found from the results that the target temperature increases with increasing ion flux from 310 °C (25 μA cm -2) to 580 °C (68 μA cm -2). Intermetallic compounds such as FeMo, Al 2Mo, Al 12Mo, Fe 7W, Fe 2W and Al 5W, were easily observed by TEM and X-ray diffraction when the flux was greater than 47 μA cm -2. In situ observation in a high voltage transmission electron microscope (HVEM) was used to investigate the structure and formation of intermetallic compounds of molybdenum-implanted H13 steel. The electron diffraction pattern of FeMo precipitates appeared at 500 °C. Recrystallization and grain growth occurred at 650 °C.

Some chemistry of half-sandwich η-arene tungsten compounds

The compounds [W(η-C6H5Me)(PMe3)3] and [W(η-C6H5Me){SiMe(CH2PMe2)3}] have been prepared from [W(η-C6H5Me)2] and tertiary phosphines. They are protonated by NH4BF4 to give [W(η-C6H5Me)(PMe3)3H]BF4 and [W(η-C6H5Me){SiMe(CH2PMe2)3}H]BF4, respectively. Reaction of [W(η-C6H5Me)(PMe3)3] with HCl gas gives the diprotonated cation [W(η-C6H5Me)(PMe3)3H2]2+. Treatment of [W(η-C6H5Me)(η-C3H5)(dmpe)]PF6[dmpe = 1,2-bis(dimethylphosphino)ethane] with LiAlH4 gives the η-methylcyclohexadienyl complex [W(η5-C6H6Me)(η-C3H5)(dmpe)], as a mixture of inseparable isomers. These have been characterised by multinuclear two-dimensional NMR spectroscopy. The fluorohydride [W(η-C6H5Me)(dmpe)H(F)] has also been prepared. The X-ray crystal structures of [W(η-C6H5Me)(PMe3)3H2][PF6]2 and [W(η-C6H5Me)(dmpe)H(F)] have been determined.

Thermal stabilities and microstructures of tungsten compound contacts on n-GaAs fabricated by low-energy ion-beam-assisted deposition

A low-energy ion-beam-assisted deposition (IBAD) technique has been developed to fabricate W-Si-N Schottky contacts of enhanced thermal stabilities on n-GaAs. By implementing remote sputtering and glancing angle low-energy N+ ion irradiation, the thermal stabilities of the W-Si-N/n-GaAs Schottky contacts were enhanced to be stable up to 850 °C, while keeping the Schottky barrier heights to the best values obtained with conventional sputtering. Thermal stabilities of the IBAD refractory metals/n-GaAs interfaces were investigated also for various W-Si-N compositions by examining the microstructure and Schottky diode characteristics. WSi0.3N0.4 showed the most stable Schottky contacts on n-GaAs of which the barrier height changed only 20 meV after thermal annealing between 700 and 850 °C, and that is proposed to be due to the stable metallurgical microstructure compared to the element tungsten and tungsten nitride.

The fluorination of scheelite by ammonium bifluoride

The interaction of scheelite with ammonium bifluoride is studied. It was shown that the scheelite reacts with NH 4HF 2 at room temperature in contrast to tungstic oxide and other tungsten compounds. Two complexes are formed: (NH 4) 3WO 3F 3 and new (NH 4) 2WO 3F 2. The compounds obtained are light fluorinated (endothermic peaks at 170 and 90°C correspondingly). The cubic monocrystals of (NH 4) 3WO 2F 5 was obtained. The cubic form is nonstable and revealed in time a lattice transformation at room temperature to more stable tetragonal form. The last one turn reversible into cubic form at 140°C. The thermal decomposition of (NH 4) 2WO 3F 2 is studied.

An XANES study of carbides of molybdenum and tungsten

The X-ray absorption near edge structure (XANES) of molybdenum and tungsten compounds has been studied by using synchrotron radiation. Substantial difference in XANES features between metals and their carbides suggested significant difference in electronic structure between them. The shift in edge position indicated charge transfer from metal to carbon when a carbide is formed. In light of a modern band theory, the larger white line areas for carbides could be interpreted as due to some of the unoccupied d-states which are not measured by x-ray white line area.

ChemInform Abstract: On the Mechanism of Oxygen Atom or Nitrene Group Transfer in Reactions of Epoxides and Aziridines with Tungsten(II) Compounds.

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Oxygen atom transfer from a phosphine oxide to tungsten(II) compounds

WCl{sub 2}(PMePh{sub 2}){sub 4} (1) reacts rapidly with Ph{sub 2}P(O)CH{sub 2}CH{sub 2}PPh{sub 2} (5, the monooxide of diphos) to give an adduct, WCl{sub 2}(Ph{sub 2}P(O)Ch{sub 2}CH{sub 2}PPh{sub 2})(PMePh{sub 2}){sub 2} (6). On being heated at 80C for 8 h, 6 rearranges by transferring the phosphoryl oxygen to tungsten, with the formation of tungsten-oxo complexes W(O)Cl{sub 2}(diphos)(PMePh{sub 2}) (7) and W(O)Cl{sub 2}(PMEPh{sub 2}){sub 3} (2), as well as WCl{sub 2}(diphos)(PMePh{sub 2}){sub 2} (8). This is the first example of oxygen atom transfer from a phosphine oxide to a metal center, a remarkable reaction because of the strength of the P-O bond (roughly 130 kcal/mol). The presence of an oxygen atom transfer step in this reaction has been confirmed by oxygen-18-labeling studies. WCl{sub 2}(PMe{sub 3}){sub 4} (9) also deoxygenates 5, forming similar and 9 indicating that the chelating nature of 5 is needed to assist the initial coordination of the phosphoryl oxygen. The kinetic barriers to deoxygenation of phosphine oxides lie both in the initial coordination of the phosphine oxide and in the actual oxygen atom transfer step. Allyl- and vinylphosphine oxides also react with 1, but oxygen atom transfer from these substrates has not been observed. 34 refs., 2 figs., 3more » tabs.« less

Metathesis of functionalized acyclic olefins

The metathesis of functionally substituted olefins, i.e olefins containing one or more heteroatoms, affords interesting prospects in the synthesis of valuable organic products. Since the first report on the successful metathesis of certain functional olefins, viz. longchain fatty acid esters, much research has been done into the possibilities of this reaction. It appears that many types of functionalized olefins undergo metathesis in the presence of a suitable catalyst. Despite the fact that many metathesis catalysts are inactive, interesting results have been obtained in the past with two catalyst systems, viz. the homogeneous system WCl 6-Sn(CH 3) 4 and the heterogeneous system Re 2O 7/Al 2O 3-Sn(CH 3) 4. The scope of the reaction of functionalized olefins has been studied for a number of groups. The functional groups suited for metathesis include -COOR, -OCOR, -COR, -OR, -CN, -OSiR 3, -Cl etc. Unsaturated carboxylic acids and alcohols can be metathesized by introducing a protecting group, e.g. a trimethylsilyl group. New homogeneous catalyst systems developed in recent years are nearly all based on tungsten compounds. Generally, however, the heterogeneous rhenium-based catalyst system turns out to be more attractive. The catalyst is active even at room temperature and can be recovered easily. In addition it is active towards certain compounds, especially allyl compounds, that are inactive with the tungsten catalysts. An important development was the access to the metathesis of unsaturated nitriles. Here, the system Re 2O 7/Al 2O 3-SnR 4 in particular gives good results. Higher activities than those observed for the Re 2O 7/ Al 2O 3 catalysts can be achieved using modified rhenium catalysts. Thus, noteworthy results were obtained when a third metal oxide was incorporated and when a different support was used, e.g. silica-alumina. These developments are the subject of further study at the present time and will lead to catalysts with activities of practical interest.

On the mechanism of oxygen-atom or nitrene-group transfer in reactions of epoxides and aziridines with tungsten(II) compounds

On the mechanism of oxygen-atom or nitrene-group transfer in reactions of epoxides and aziridines with tungsten(II) compounds

Preparation and structure of trichlorotris(dimethylphenylphosphine)tungsten(III), the first structurally characterised neutral mononuclear complex of tungsten(III)

A mononuclear complex of tungsten(III) has been obtained by the zinc reduction of [WCl4(PMe2Ph)3]. This product, [WCl3(PMe2Ph)3], has an octahedral, meridional configuration, and crystallises in the space group P21/c, with a= 16.177(2), b= 10.350(1) and c= 18.079(2)A, β= 113.81(6)°. It can be used to prepare other mononuclear tungsten(III) compounds. Its structural relationship with other complexes, [MCl3(PMe2Ph)3](M = Re, Os or Ir), is discussed.

Bis[1,2-bis(dimethylphosphino)ethane] dichlorotungsten(II) and its reactions. X-ray crystal structures of bis[1,2-bis(dimethylphosphino) ethane]tetrachlorotungsten(V) hexachloroantimonate(V) and bis{bis[1,2-bis(dimethylphosphino)ethane] tetrahydroaluminatohydridomolybdenum(II)}

The reduction of WCl 4(THF) 2 by sodium naphthalenide in the presence of 1,2-bis(dimethylphosphino)ethane (DMPE) in tetrahydrofuran affords trans-WCl 2(DMPE) 2. Interaction of this complex with NaBPh 4 in MeCN gives [WCl(η 2-MeCN)(DMPE) 2]BPh 4 and with SbCl 5 the tungsten(V) complex [WCl 4(DMPE) 2]SbCl 6. The X-ray crystal structure of the latter shows the cation to have dodecahedral geometry with equatorial chlorine atoms. Interaction of trans-MCl 2(DMPE) 2 (M = Mo and W) with LiAlH 4 gives the hydrido aluminohydrides, [MH(AlH 4)(DMPE) 2] 2, and the X-ray crystal structure of the molybdenum compound has been determined. Methanolysis of the tungsten compound gives WH 4(DMPE) 2.

Surface Studies of Laser Processing of W on GaAs from WF6

AbstractLaser Chemical Vapor Deposition of tungsten on GaAs from WF6 using a focused cw scanning argon-ion laser beam has been investigated. Lines have been produced using different mixtures of WF6:H2 and WF6:SiH4 and in some cases, without any reducing gas. Depositions are found to occur within a narrow process window, and are difficult to reproduce. In order to understand this process, we have performed surface analysis on GaAs samples exposed to WF6. X-Ray Photoelectron Spectroscopy studies on the interaction between WF6 and GaAs in the absence of laser illumination show that fluorinated tungsten compounds are present on the GaAs surface. Furthermore, the existence of a chemical reaction leading to the formation of GaF3 at the surface and to a loss of the stoichiometry of the substrate surface is detected. Possible mechanisms, and the effects of these reactions on the deposition process are discussed.

Übergangsmetall-carbin-komplexe XCVIII. N-Alkylierung eines ethylisocyanid-liganden am molybdän(0); Synthese und oxidationsreaktionen erster cyclopentadienyl-substituierter molybdän-diethylaminocarbin-komplexe

A large scale, high yield synthesis of the first cyclopentadienyl-substituted diethylaminocarbyne complexes of molybdenum has been developed starting from (η 5-C 5H 5)Mo(CO) 3I ( 1). In the first step of the synthetic procedure 1 is quantitatively transformed with EtNC in CH 2Cl 2 into an isomeric mixture of cis- and trans-(η 5-C 5H 5)Mo(CO) 2(EtNC)I ( 2a, 2b). The isomers 2a and 2b are then quantitatively reduced with sodium powder to the zerovalent molybdenum complex Na[(η 5-C 5H 5)Mo(CO) 2(EtNC)] ( 3). The ethylisocyanide ligand in 3 is susceptible to electrophilic attack at nitrogen. Thus reaction of 3 with Et 3OBF 4 gives as the major product, the low valent diethylaminocarbyne complex (η 5-C 5H 5)(CO) 2MoCNEt 2 ( 4). A minor product, the η 2-iminoacyl complex (η 5-C 5H 5)(CO) 2Mo[η 2-C(NEt)Et] ( 5), is also formed in this reaction via electrophilic attack on the electron rich metal center of 3. Compounds 4 and 5 are separated by column chromatography and isolated as yellow and red, microcrystalline solids in 60 and 8% yield respectively. Oxidative decarbonylation of 4 with I 2 and Br 2 leads to the high valent diethylaminocarbyne complexes (η 5-C 5H 5)(I) 2(CO)MoCNEt 2 ( 6) and (η 5-C 5H 5)(Br) 2-(CO)MoCNEt 2 ( 7), isolated as thermally stable, black and purple solids in quantitative yield. Composition and structure of the complexes 2a–7 were determined by total elemental analyses, IR, 1H NMR and 13C NMR spectra and the spectral data compared with the analogous tungsten compounds.

Molybdenum and tungsten complexes with metallo-ligands having sulfur donor atoms

The reaction of Mo(CO) 6 with 2,3-pentanedione- bis(β-mercaptoethylimino)nickel(II), Nipe, under mild conditions, results in the formation of NipeMo(CO) 4, while more forcing conditions give a different product, [NipeMo(CO) 3] 2. From an analogous reaction, a tungsten compound of the latter formula was also isolated. The chromium analogue was prepared in a similar manner but lacked the purity necessary to give good analyses. The molybdenum and tungsten complexes were characterized by chemical analyses and solution molecular weight. The magnetic moments of these complexes are anomalous, 2.3–2.4 BM, and suggest that the coordination number of the nickel is greater than four. Electronic spectra support this hypothesis. Cyclic voltammetry data indicate that the M(CO) 3 moiety withdraws electron density from the nickel ion in the metallo-ligand. Reactions of Mo(CO) 6 and W(CO) 6 with bis(2-mercaptoethylamine)nickel(II) (Ni(MEA) 2) gave the complexes Ni(MEA) 2M 2(CO) 10 (M = Mo, W) which were characterized by analyses and infrared and electronic spectra.

New fluxional seven-co-ordinate molybdenum(II) and tungsten(II) complexes: X-ray structure of the pyridine-2-thionato complex [W(C5H4NS)2(CO)2(PMe2Ph)

The reaction of [W(CO)3(MeCN)3] with pyridine-2-thione (pySH) at room temperature gives the tungsten(II) compound [W(pyS)2(CO)3](1) and the tungsten(0) compound [W(CO)5(pySH)](2). To slow the rate of intramolecular exchange of the pyS ligands in (1), PMe2Ph was introduced to give [W(pyS)2(CO)2(PMe2Ph)](4). Crystals of (4) are monoclinic space group C2/c, a= 30.738(9), b= 9.867(2), c= 16.048(9)A, β= 121.04(3)°, and Z= 8 and the X-ray structure was refined to R= 0.0330 and R′= 0.0335. Molecules of (4) contain two chelating pyS ligands and the tungsten is seven-co-ordinated. Approximately determined exchange rates for the diastereotopic Me groups of PMe2Ph and of the non-equivalent pyS ligands are the same indicating that both exchanges result from the same process. The corresponding molybdenum compound is isostructural and shows similar fluxionality.

Os3(CO)12Cl(SnCl2){cpM(CO)3}]: heteropentametallic chain cluster complexes with no bridging ligands (cp =η5-cyclopentadienyl; M = Mo or W)

The title compounds have been prepared in high yields by the reactions of Na[cpM(CO)3] with [Os3(CO)12Cl(SnCl3)](cp =η5-C5H5) and the tungsten compound has been shown, by X-ray crystallography, to contain a pentametallic chain held together only by metal–metal bonds.

Reactions of carbon dioxide with electron-rich trimethylphosphine compounds of rhenium and tungsten: crystal structure of [W(PMe3)4H2(CO3)

The new compounds trans-[Re(PMe3)4(CO)(O2CH-O)],cis-[Re(PMe3)4(CO)H],trans-[Re(PMe3)4(CO)I]trans-[Re(PMe3)4(CO)Cl], trans-[Re(PMe3)4{η2-SC(O)}H], [Re(PMe3)5H2][BF4], [Re(PMe3)4(CO)H2][BF4], [Re(PMe3)5I],[W(PMe3)4H2(CO3)], and [Ru(PMe3)3(CO)(CO3–OO′)] are described. The crystal structure of [W(PMe3)4H2(CO3)] has been determined.

The use of silylethers and silylthioethers in syntheses of oxohalide and thiohalide compounds of molybdenum and tungsten

Convenient procedures for the preparation of molybdenum and tungsten oxo- and thiohalides are described which exploit reactions between transition metal halides and bis(silyl)ether and -thioether reagents, according to the general equation: MCI x+(Me 3Si) 2Y (Y = O,S)→M(Y)Cl x−2+2Me 3SiCl. W(O)Cl 4 ( 1) and Mo(O)Cl 3 ( 5) are formed in high yield by room temperature treatment of WCl 6 and MoCl 5 with (Me 3Si) 2O in CH 2Cl 2 solvent. Mo(O) 2Cl 2 ( 6) may be obtained from Mo(O)Cl 4 by an analogous room temperature procedure; efficient generation of W(O) 2Cl 2 ( 2) requires warming of W(O)Cl 4 with (Me 3Si) 2O at 80°C in octane. In acetonitrile solvent, W(O)Cl 4 reacts with one equivalent of (Me 3Si) 2O to give W(O) 2Cl 2(CH 3CN) 2 ( 3) in 70% yield. Treatment of W(O)Cl 4 with two equivalents of (Me 3Si) 2O in CH 2Cl 2 leads to blue crystalline W(O) 2Cl(OSiMe 3) ( 4), which is stable to elimination of Me 3SiCl to 1OO°C. W(S)Cl 4 ( 7), W(S) 2Cl 2 ( 8) and Mo(S)Cl 3 ( 9) are obtained by low temperature treatment of WCl 6, W(S)Cl 4 and MoCl 5, respectively, with one equivalent of (Me 3Si) 2S in CH 2Cl 2 solvent. The mixed oxothiohalide compounds W(O)(S)Cl 2 ( 10) and Mo(O)(S)Cl 2 ( 11) may be isolated in good yield through the reaction of W(O)Cl 4 or Mo(O)Cl 4 with (Me 3Si) 2S in CH 2Cl 2 at low temperature.

Oxidation of petroleum sulphides by hydrogen peroxide in the presence of compounds of metals of varying valency

An important feature of vanadium, tungsten and molybdenum compounds is their proneness to form complexes of different degrees of stability with many substances, including sulphides. Hydrogen peroxide is also a complex-forming compound [1]. A number of researchers [2] believe that, during the oxidation of sulphides, the movement of oxygen to sulphide occurs via a complex of polarized peroxide and sulphide, and therefore compounds of the above metals can be expected to have a catalytic effect on the oxidation of petroleum sulphides to sulphoxides. It is also of interest to study the oxidation of sulphides in the presence of iron compounds. Microimpurities of the latter always accompany petroleum distillates on account of corrosion of piping and equipment.

Schottky Properties of Tungsten Compounds Refractory Contacts on n-GaAs Fabricated by Ion Beam Assisted Deposition

AbstractA low energy ion beam assisted deposition (IBAD) technique has been developed to fabricate refractory W-Si-N films for the application to gate electrode of GaAs metal-semiconductor field effect transistors( MESFETs ). Thermal stability of the IBAD refractory metal/n-GaAs interface was investigated by examining the microstructure and Schottky diode characteristics. The Schottky barrier heights of 0.71, 0.84, and 0.76 eV were obtained after thermal annealing at 850°C for the W/, WN0.27/, and WSi0.3N0.4/GaAs diodes, respectively, and these values are comparable to those of the best results published with conventional reactive sputtering. While some crystalization of the deposit and reaction between film and substrate at the interface were observed with TEM for the W/ and WN/GaAs contacts annealed at 800°, the WSiN film remained amorphous and showed clear interface with the GaAs substrate without significant morphological change. The WS0.3N0.4/GaAs diode showed good thermal stability of Schottky barrier heights with only 20 meV variation in the temperature range between 700 and 850°C, and that is proposed to be due to the stable microstructure.