Tungsten rhenium, and

Klotzbiicher WE, Ozin GA (1980) Optical spectra of hafnium, tungsten, rhenium and mthenium atoms and other heavy transition-metal atoms and small clusters (Zrl, 2, Pdl, 2, Aul, 2, 3) in noble-gas matrixes. Inorg Chem 19 3767-3776... 

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

Molecular wires, 208 211 in which two metal centers are connected by an unsupported C3 chain, as in compound 191, have been generated by addition of BF3 to binuclear bridged (l-alkynyl)carbene complex lw (Scheme 80).27 29,212 Similar compounds were derived from tungsten, rhenium, and iron moieties. A binuclear complex 192 containing a C5 bridge has been also obtained 27... 

Obviously, the 4f - 5 p crossing does not correspond to an electric dipole transition, but to an electric quadrupole moment. It has no clear-cut effect in photo-electron spectra of tungsten, rhenium and osmium, suggesting that the non-diagonal elements of the effective one-electron operator are smaller than 0.3 eV. It would be worthwhile to study volatile molecules such as WF6 or 0s04 under conditions of high resolution using either the continuous spectrum emitted by a synchrotron, or 132.3 eV photons from an yttrium anti-cathode (20, 21). 

The enolates (48) and (49) of the transition metals tungsten, rhenium and molybdenum can be successfully prepared by the nucleophilic displacement of a-chloro ketones and a-chloro esters with the appropriate transition metal anion (Scheme 6). They are isolated as C-bound enolate derivatives and, except for the rhenium enolate (49), do not undergo thermal aldol additions to benzaldehyde. However, Bergman and Heathcock et al. have found that an aldol reaction of complex (48) with benzaldehyde can occur on irradiation via the rearranged q -oxaallyl derivative (50), where the metal aldolate (51) can then be... 

Tetrahydroborate complexes with third-row transition metals are much less abundant than for first or second row metals. Only complexes with lanthanum, hafnium, tungsten, rhenium and osmium have been characterised by diffraction techniques. For each metal, only a few compounds are known, making conclusions less reliable regarding the M - B distances. 

Complexes of tungsten, rhenium, and ruthenium of 4-py-DTEf and 4-py2-DTf have been developed by Lehn [56, 57]. These complexes exhibit good photoch-romic properties. A switching of fluorescence between their open and closed forms is observed when excited at 240 nm, a wavelength of irradiation that almost did not affect the state of the molecule. 

No infomiation has been found in the literature for phase equihbria and isothermal sections of ternary R-5compounds with ideal compositions have been investigated. The systems with hafnium, tantalum, tungsten, rhenium, and osmium as 5d-element have not been studied. The Pm-5[Pg.33]

Cerium, Samarium, Titanium, Cobalt, Vanadium, Tungsten, Rhenium, and Molybdenum... 

One problem encountered in all experiments on fluid metals is the difficulty of confining samples at high temperatures without contamination from reactions with the cell material. Only a few materials are suitable. For studies of mercury and the alkali metals near their criticeil points, acceptable materials include pure tungsten, molybdenum, and the alloys tungsten-rhenium and tungsten-molybdenum. Sintered aluminum oxide or single crystal sapphire may be used to contain alkali metals up to about 1500 °C and to somewhat higher temperatures for mercury. 

A. Neuhaus, A. Veldkamp, and G. Frenking, Inorg. Chem., 33, 5278 (1994). Oxo and Nitrido Complexes of Molybdenum, Tungsten, Rhenium and Osmium. A Theoretical Study. Theoretical Studies of Inorganic Compounds. IV. 

Since detailed chemical structure information is not usually required from isotope ratio measurements, it is possible to vaporize samples by simply pyrolyzing them. For this purpose, the sample can be placed on a tungsten, rhenium, or platinum wire and heated strongly in vacuum by passing an electric current through the wire. This is thermal or surface ionization (TI). Alternatively, a small electric furnace can be used when removal of solvent from a dilute solution is desirable before vaporization of residual solute. Again, a wide variety of mass analyzers can be used to measure m/z values of atomic ions and their relative abundances. 

Molybdenum hexafluoride is used in the manufacture of thin films (qv) for large-scale integrated circuits (qv) commonly known as LSIC systems (3,4), in the manufacture of metallised ceramics (see MetaL-MATRIX COMPOSITES) (5), and chemical vapor deposition of molybdenum and molybdenum—tungsten alloys (see Molybdenumand molybdenum alloys) (6,7). The latter process involves the reduction of gaseous metal fluorides by hydrogen at elevated temperatures to produce metals or their alloys such as molybdenum—tungsten, molybdenum—tungsten—rhenium, or molybdenum—rhenium alloys. 

Rhenium hexafluoride is a cosdy (ca 3000/kg) material and is often used as a small percentage composite with tungsten or molybdenum. The addition of rhenium to tungsten metal improves the ductility and high temperature properties of metal films or parts (11). Tungsten—rhenium alloys produced by CVD processes exhibit higher superconducting transition temperatures than those alloys produced by arc-melt processes (12). 

Tungsten with the addition of as much as 5% thoria is used for thermionic emission cathode wires and as filaments for vibration-resistant incandescent lamps. Tungsten—rhenium alloys are employed as heating elements and thermocouples. Tantalum and niobium form continuous soHd solutions with tungsten. Iron and nickel are used as ahoy agents for specialized appHcations. 

ASTM E988-96. Standard Temperature-Electromotive Force (FMF) Tables for Tungsten-Rhenium Thermocouples. American Society for Testing and Materials, 1996. 

Donaldson, J. G., APreliminary Study ofthe Vapor Deposition of Rhenium and Rhenium-Tungsten, V. ofthe Less CommonMetals, 14 93-101(1968)... 

Field emission microscopy was the first technique capable of imaging surfaces at resolution close to atomic dimensions. The pioneer in this area was E.W. Muller, who published the field emission microscope in 1936 and later the field ion microscope in 1951 [23]. Both techniques are limited to sharp tips of high melting metals (tungsten, rhenium, rhodium, iridium, and platinum), but have been extremely useful in exploring and understanding the properties of metal surfaces. We mention the structure of clean metal surfaces, defects, order/disorder phenomena,... 

The work cited in sections 2.4 and 2.5 is representative of the SN1 substitution reactions of metal carbonyls. However, a much more extensive and detailed account has recently been published covering similar reactions of vanadium, chromium, molybdenum, tungsten, rhenium, iron and nickel carbonyls in addition to those of manganese and cobalt2 9a. 

Because of the importance of olefin metathesis in the industrial production of olefins and polymers, many different catalysts have been developed. Almost all of these are transition metal-derived, some rare exceptions being EtAlCl2 [758], Me4Sn/Al203 [759], and irradiated silica [760]. The majority of catalytic systems are based on tungsten, molybdenum, and rhenium, but titanium-, tantalum-, ruthenium-, osmium-, and iridium-based catalysts have also proven useful for many applications. 

B. Mononuclear Compounds of Iron, Molybdenum, Tungsten, Rhenium, Platinum, Nickel and Cobalt... 

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