Tungsten solid-state synthesis

The belt apparatus (Fig. 7.3) provides an ideal high pressure-high temperature combination for solid-state synthesis. This apparatus was used for the synthesis of diamonds some years ago. It actually involves a combination of the piston-cylinder and the opposed anvil designs. The apparatus consists of two conical pistons made of tungsten carbide, which ram through a specially shaped chamber from opposite directions. The chamber and pistons are laterally supported by several steel rings,... 

The application of ly transition metal carbides as effective substitutes for the more expensive noble metals in a variety of reactions has hem demonstrated in several studies [ 1 -2]. Conventional pr aration route via high temperature (>1200K) oxide carburization using methane is, however, poorly understood. This study deals with the synthesis of supported tungsten carbide nanoparticles via the relatively low-tempoatine propane carburization of the precursor metal sulphide, hi order to optimize the carbide catalyst propertira at the molecular level, we have undertaken a detailed examination of hotii solid-state carburization conditions and gas phase kinetics so as to understand the connectivity between plmse kinetic parametera and catalytically-important intrinsic attributes of the nanoparticle catalyst system. 

The synthesis of the first quadruply bonded tungsten(II) car-boxylate, W2(02CCF3)4 (hereafter referred to as V TFA) ), was reported by us last year (1). The structure of its diglyme adduct, W2(TFA)4 2/3 diglyme is shown in Figure 1. This particular view shows the partial contents of two unit cells and it emphasizes the tridentate nature of the axially coordinated polyether which "stiches" W2(TFA) units together in the solid state. We now have in hand several other adducts of W2(TFA) and one of these, W2(TFA)4 2PPh3 (an axial adduct), has been structurally characterized (2). Despite many attempts, X-ray quality crystals of unsolvated W2(TFA) have not been obtained. 

We have been interested in developing new routes to mesostructured metal sulfides. Our approach capitalizes on well-established solution condensation reactions that can transform discrete, soluble metal thiolate species into solid-state metal sulfide compounds. Here we wish to describe the use of (NH4)2WS4 as a precursor material in the synthesis of three mesostructured tungsten suldifes with the inorganic walls that consist of continuous WS3 chains and WS2. 

Blue-green OSOF4 (m.p. 80°C) is a byproduct in the synthesis of OsOFs and can also be made in small quantities by reduction of OSOF5 on a hot tungsten wire. In the gas phase it has a C4V pyramidal structure (0s=0 1.624 A, Os—F 1.835 A) crystallography suggests a solid-state structure similar to tetrameric OsFs the more complex IR spectrum of the solid is in keeping with this [29]. 

Slater PR, Irvine ITS (1999) Niobium based tetragonal tungsten bronzes as potential anodes for solid oxide fuel cells synthesis and electrical characterisation. Solid State Ionics 120 125-134... 

Chromium, Molybdenum and Tungsten The intramolecular rotational behaviour of a series of highly substituted Ti -arene chromium and molybdenum compounds has been examined in detail. Dynamic processes in the solid state, using spin-lattice relaxation time measurements, have been studied for two structurally characterised polymethyl benzenechromium tricarbonyl complexes. The mechanism of migration of the Cr(CO)3 unit from the six to the five membered ring in indenyl anions has been reported. The synthesis and cyclic voltammetry of (Ti -phenylmethylsila-14-crown-5)chromiumtricarbonyl has appeared. ... 

Reports of new tungsten complexes include the reaction of the transient species W(CO)5(cyclohexane) with cyclo-C4H 0 (n = 4, 6, 8) studied by time-resolved infrared absorption spectroscopy. Schultz and co-workers have noted an unusual solvent isotope effect in the reaction of W(CO)5(solv) (solv = cyclohexane or cyclohexane-rfu) with TFIF. Some interesting chemistry involving W(CO)5(2,5-dihydrofuran) is noted by the same group. Adducts of cyclotriphosphorus complexes have been reported by Di Vaira and co-workers, leading to the synthesis, solid state structure and solution behaviour of the bis-adducts [ (MeC(CH2PPh2)3)Co (P3)(M(CO)5 2], where M is a Group 6 metal. 

---