Molybdenum oxide halides

Recently, Stair and coworkers [10, 11] developed a method to produce gas-phase methyl radicals, and used this to study reactions of methyl groups on Pt surfaces [12] and on molybdenum oxide thin films [13]. In this approach, methyl radicals are produced by pyrolysis of azomethane in a tubular reactor locat inside an ulttahigh vacuum chamber. This method avoids the complications of co-adsorbcd halide atoms, it allows higher covraages to be reached, and it allows tiie study of reactions on oxide and other surfaces that do not dissociate methyl halides effectively. 

ANHYDROUS MOLYBDENUM HALIDES AND OXIDE HALIDES—A SUMMARY... 

The known oxide halides of molybdenum are listed below TABLE I... 

Reduction of the Oxides, Halides, or Sulphides with Hydrogen.— Molybdenum trioxide, purified by sublimation in a platinum tube, is heated in pure hydrogen first at as low a temperature as possible in order to convert it to the dioxide MoOg, and finally in hydrogen in a quartz or platinum tube at a high temperature in order to complete the reduction. Certain modifications in the teehnique of the process have been described. ... 

In the kinetic interpretation of ECL data presented above the closest approach of reactants has been assumed. It seems to be fulfilled in the case of organic ECL systems (because of the Coulombic attraction between oppositely charged ions). In contrast, in ECL systems involving identically charged transition-metal complexes, Coulombic repulsion may lead to an increase in the electron transfer distance. The molybdenum(II) halide cluster ion MoeCliJ [197-199] is the one of the best-understood examples. In electrochemical reactions MogCliJ is reversibly reduced or oxidized to stable MosCl and Mo6Cl["4 respectively ... 

Traditionally, PE has tended to be classed as low, medium, or high density. These sub-divisions have never been precisely defined. High-pressure polymerisation of ethylene takes place by a free radical process, medium-pressure polymerisation occurs in the presence of molybdenum oxide or chromium oxide (Phillips process), while for low- and medium-pressure polymerisation transition metal halide and alkylaluminium compounds (Ziegler process) are used. Some properties of PE obtained from various ethylene processes are presented in Figure 1.2. 

Fig. 6.1b) in which twelve inner ligands bridge the edges of the Me octahedron, and six outer ligands occupy apical positions, predominate. These units are found in reduced zirconium, niobium, tantalum, and rare-earth halides, and niobium, tantalum, molybdenum and tungsten oxides [la, 6, 10]. 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

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