Valence intermediate

Values of the single-bond radii for the metals of the series silver to tin and gold to lead are also given in table 6, as calculated by equations (10c) and (11c) for the pure valence states A, B, C and D and for certain intermediate valencies, corresponding to resonance among these states. 

Rare-earth ions inserted in the tetraborides have the 34- oxidation state, except for CeB4 and YbB4 (see Fig. 2). The abnormal volume contraction for the CeB4 unit cell can be explained by the presence of some Ce ions . Recoilless y-ray emission spectra and magnetic measurements indicate that ytterbium in YbB4 has an intermediate valence state as in YbAl3... 

The rare earths in their dodecaborides have the 3 + oxidation state except for Yb and Tm which have an intermediate valence state. A recoilless y-ray emission spectrum study of TmB,2 shows no magnetic ordering at 1.35 K the spectra of YbB,2 reveal no magnetic structure to 1.35 K. The compounds HoB,2, ErB,2 order antiferromagnetically, and ZrB,2 and LuB,2 become superconducting < 5.8 K and < 0.48 K, respectively. ... 

The oxidation of tartaric and glycollic acid by chromic acid also induces the oxidation of manganous ions. In the presence of higher concentrations of manganese(II) the rate of oxidation of the acids is diminished to about one-third of that in the absence of manganous ions. The decrease of the rate has been attributed to manganese(II) catalysis of the disproportionation of the intermediate valence states of chromium probably chromium(IV). 

He suggested that the ionic formulas, like the nonionic formulas, "represent formulations of extremes" and that no bond across the ring is required. Using the hypothesis of the motions of valence electrons, as developed by Stark and Kossel, Arndt suggested the possibility of intermediate valence states (Zwitterstufen) as well.32 Independently, Robinson proposed possible electronic shifts in pyrones and similar systems, but he did not state the idea of a definite "intermediate state" of the molecule between the ionic and uncharged formulas.33... 

Cathodic stripping voitammetry (CSV) is more rarely required than ASV, but is useful for the determination of halide(s), sulfide or other anions. Occasionally, cations of intermediate valency, such as or can be analysed by using CSV, e.g. by reducing cations within a layer of metal oxide on an electrode made of carbon. 

When an ion is transferred between two phases an intermediate valency species is not possible. However, in the transfer of Cu from a metal electrode into an electrolyte it is possible that the reaction mechanism is ... 

All these data verify that in real systems, the rate of electron transfer between components of a conductive chain is high. There are states of a mixed valence. Enhanced electric conductivity and other unusual physical properties are widespread among those inorganic or coordination compounds that contain metals in intermediate -valence states. In cases of organic metals, nonstoi-chiometric donor/acceptor ratios provide even better results. For example, the salt of (TTF)i (Br)oj composition displays an electric conductivity of 2 X 10 cm while (TTF)i(Br)i salt does not... 

Generally, the reduction is achieved under deaerated conditions to avoid a competitive scavenging of Cjoiv and H atoms by oxygen. These atoms are as homogeneously distributed as the ions and the reducing species, and they are therefore produced at first as isolated entities. Similarly, multivalent ions are reduced by multistep reactions, including disproportionation of intermediate valencies. Such reduction reactions have been observed directly by pulse radiolysis for a variety of metal ions (Fig. 2), mostly in water [28], but also in other solvents where the ionic precursors are soluble. Most of their rate eonstants are known and the reactions are often diffusion controlled. 

Displacement of the cation towards a face gives three primary and three secondary bonds and is favoured by low-valence cations such as Tl" ". Cations with intermediate valence, e.g. Sn +, tend to move towards an edge giving four primary and two secondary bonds while high-valence cations such as Xe " " favour displacement towards a corner to give five primary bonds (one strong... 

The complexity of the situation may be illustrated by tracing the development of our knowledge of chromia catalysts. It is now clear that Cr ions on the surface may occur in valence states from Cr11 to CrVI all intermediate valence states have been shown to occur, and all are possible in a regime of temperature and gas composition where the thermodynamically stable bulk phase is Cr2C>3. 

The position of the ASV peak on the voltage scan reflects the nature of the ion being reduced, and for complex ions the peak position moves to more negative potentials as stability increases. In some cases formation of intermediate valency states (e.g. in chloride solution, Cu2+ — Cu+ — Cu°) results in split peaks. Adsorption of species (e.g. colloidal particles, surfactants) on the mercury electrode also causes peak movement (generally in an anodic direction). 

Wachter, P. Intermediate valence and heavy fermions, in Gschneidner Jr., K.A., Eyring, L., editors. Handbook on the Physics and Chemistry of Rare Earths. Amsterdam North-Holland Publishing Company 1994, chap. 132. 

Keywords Fullerenes Superconductivity Antiferromagnetism Metal-insulator transition Electron correlation Intermediate valence... 

Intermediate Valence Behaviour and Lattice Response of Sm2.75C60... 

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