Valence states, noble metals

Ruthenium and osmium are decidedly less noble than the other four metals of the platinum group. Both exist in numerous valency states and very readily form complexes. Ruthenium is not attacked by water or non-complexing acids, but is easily corroded by oxidising alkaline solutions, such as peroxides and alkaline hypochlorites. 

This FLAPW-SIC scheme has been applied to the CP calculations of Cu, Si and diamond. The semiconductor Si and the insulator diamond have energy gaps and the most upper valence electrons are regarded as being a slightly bound state. The noble metal Cu has tightly bound d-electrons. 

Reductive elimination is simply the reverse reaction of oxidative addition the formal valence state of the metal is reduced by two (or one in a bimetallic reaction), and the total electron count of the complex is reduced by two. While oxidative addition can also be observed for main group elements, this reaction is more typical of the transition elements in particular the electronegative, noble metals. In a catalytic cycle the two reactions always occur pair-wise. In one step the oxidative addition occurs, followed for example by insertion reactions, and then the cycle is completed by a reductive elimination of the product. 

Noble metals, which are easily reduced to zero-valence state by polyols. 

Chapter 3, by Rolando Guidelli, deals with another aspect of major fundamental interest, the process of electrosorption at electrodes, a topic central to electrochemical surface science Electrosorption Valency and Partial Charge Transfer. Thermodynamic examination of electrochemical adsorption of anions and atomic species, e.g. as in underpotential deposition of H and metal adatoms at noble metals, enables details of the state of polarity of electrosorbed species at metal interfaces to be deduced. The bases and results of studies in this field are treated in depth in this chapter and important relations to surface -potential changes at metals, studied in the gas-phase under high-vacuum conditions, will be recognized. Results obtained in this field of research have significant relevance to behavior of species involved in electrocatalysis, e.g. in fuel-cells, as treated in chapter 4, and in electrodeposition of metals. 

The leading effect of the full d shells should come from the coupling with the empty states nearest in energy, the valence s states of the noble metal. Such... 

Semiempirical calculations of free energies and enthalpies of hydration derived from an electrostatic model of ions with a noble gas structure have been applied to the ter-valent actinide ions. A primary hydration number for the actinides was determined by correlating the experimental enthalpy data for plutonium(iii) with the model. The thermodynamic data for actinide metals and their oxides from thorium to curium has been assessed. The thermodynamic data for the substoicheiometric dioxides at high temperatures has been used to consider the relative stabilities of valence states lower than four and subsequently examine the stability requirements for the sesquioxides and monoxides. Sequential thermodynamic trends in the gaseous metals, monoxides, and dioxides were examined and compared with those of the lanthanides. A study of the rates of actinide oxidation-reduction reactions showed that, contrary to previous reports, the Marcus equation ... 

Electronic properties of transition metals can be described by a simplified model, which, essentially considers a narrow d sub-band having a somewhat localised, atomic-like nature, while the sp sub-band is wider and mostly delocalised.1 The Fermi level has a major contribution to the density of states from the d band in most typical active phases, such as those including noble metals. The limited size of clusters produces the so-called quantum or size confinement effects. These essentially arise from the presence of discrete, atomic-like electronic states. From the solid state point of view, the electronic states of clusters can be considered as being a superposition of bulk-like states with concomitant increases in oscillator strength.14 This separation of the states is visible in the valence band of metallic clusters synthesised by physical methods3 but is obscured in... 

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