Transition-metal binary compounds Subject

The factors determining the particular structure adopted hy an intermetallic compound or, indeed, whether such a compound exists at all as a single-phase material, have been the subject of much discussion for a considerable period of time. The Hume-Rothery rules for electron compound formation will he very familiar and are related physically to the size of the Fermi sphere in the appropriate Brillouin zone. For example, electron compounds are expected for valence electron concentrations of , fj and l for the bcc, y-brass and cph structures, respectively. The interplay of other factors such as the atomic size, solubility and crystal structure of the components on the formation of intermetallic compounds has been considered in considerable detail by many workers, including Yao (1962), who suggested that transition metal binary systems could be classified into groups according to an excess energy dE expressed as... 

In addition to the binary catalysts from transition metal compounds and metal alkyls there 2ire an increasing number which are clearly of the same general type but which have very different structures. Several of these are crystalline in character, and have been subjected to an activation process which gives rise to lattice defects and catalytic activity. Thus, nickel and cobalt chlorides, which untreated are not catalysts, lose chlorine on irradiation and become active for the polymerization of butadiene to high cis 1,4-polymer [59]. Titanium dichloride, likewise not a catalyst, is transformed into an active catalyst (the activity of which is proportional to the Ti content) for the polymerization of ethylene [60]. In these the active sites evidently react with monomer to form organo-transition metal compounds which coordinate further monomer and initiate polymerization. 

Contents Theory of Electrons in Polar Fluids. Metal-Ammonia Solutions The Dilute Region. Metal Solutions in Amines and Ethers. Ultrafast Optical Processes. Metal-Ammonia Solutions Transition Range. The Electronic Structures of Disordered Materials. Concentrated M-NH3 Solutions A Review. Strange Magnetic Behavior and Phase Relations of Metal-Ammonia Compounds. Metallic Vapors. Mobility Studies of Excess Electrons in Nonpolar Hydrocarbons. Optical Absorption Spectrum of the Solvated Electron in Ethers and Binary Liquid Systems. Subject Index. Color Plates. 

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