Transition metal hydrides chemical properties

Crystal structures and properties of the binary transition metal hydrides underscore the difficulty of a strict categorization of metal hydrides according to their chemical... 

One of new methods of magnesium, transition and rare-earth metals hydrides and their compounds obtaining is mechanical-chemical method. Numerous quantity of works are devoted to the improving kinetic, sorption properties of hydrides which were treated mechanically or were obtained by this method in hydrogen medium under pressure [1-7]. Great consideration is given to the influence of dispersity on phase equilibrium. At the same time the investigation of mechanical... 

In view of the fact that the probability of the molecular electron shell restructuring is due solely to the atom nearest to the radioactive one, in Fig. 3 we show the dependence of the probability (of remaining in the ground state) on the ionization potential /f for the shell of the atom nearest to He which is most distorted by the transition T - He+. As follows from Fig. 3, for metal hydrides there is a linear dependence on the potential For nonmetals (C, O, or F) the probability is independent of Apparently, the obtained dependence on /, is an illustration of the degree of ionicity of the chemical bond. As a whole, the problem of the influence of properties of an immediate neighbor of the radioactive atom on the /1-decay-induced excitations of the molecule requires further study. 

The hydrides show the chemical and physical properties one would anticipate from the position of the metal in the periodic table and from the foregoing. The strongly electropositive metals of the first two groups give saline hydrides which physically resemble the corresponding fluorides. The transition metals form metallic or semimetallic hydrides, presumably because of their ability to use d or d-hybrid orbitals which are delocalized into a conduction band. Apart from their metallic character, however, there are no unexpected differences in proper-... 

Transition metal polyhydride complexes are remarkable for a number of reasons. Most of them are related to the peculiar chemical properties of the metal-hydride combination. There are, however, some specific phenomena in... 

There seems to be some confusion about the polarization of the metal-hydrogen bond in certain hydrido-transition metal-carbonyl compounds, in particular HCo(CO)4. This and some related hydrido-carbonyl compounds are slightly soluble in water, and such solutions are clearly acidic In the gas phase or in non-polar solvents, however, these complexes exhibit spectroscopic and chemical properties similar to those of other non-acidic hydride complexes. A MO calculation of the charge densities in HCo(CO)4 indicated that 1.6 electrons are associated with the hydrogen atom, and the question was discussed as to how a molecule with a negative-... 

Metals and alloys, the principal industrial metalhc catalysts, are found in periodic group TII, which are transition elements with almost-completed 3d, 4d, and 5d electronic orbits. According to theory, electrons from adsorbed molecules can fill the vacancies in the incomplete shells and thus make a chemical bond. What happens subsequently depends on the operating conditions. Platinum, palladium, and nickel form both hydrides and oxides they are effective in hydrogenation (vegetable oils) and oxidation (ammonia or sulfur dioxide). Alloys do not always have catalytic properties intermediate between those of the component metals, since the surface condition may be different from the bulk and catalysis is a function of the surface condition. Addition of some rhenium to Pt/AlgO permits the use of lower temperatures and slows the deactivation rate. The mechanism of catalysis by alloys is still controversial in many instances. 

Hydrogen combines with most of the chemical elements. Here we concentrate on binary hydrides of the typical elements, ignoring those of the transition elements, lanthanides and actinides, which often have metallic properties and so resemble alloys. Binary hydrides are compounds of hydrogen and one other element. A useful classification of the highest hydrides of the typical elements is shown in Figure 5.9. It divides them into three classes salt-like, macromolecular and molecular. 

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