Divalent states

Selective Reduction. In aqueous solution, europium(III) [22541 -18-0] reduction to europium(II) [16910-54-6] is carried out by treatment with amalgams or zinc, or by continuous electrolytic reduction. Photochemical reduction has also been proposed. When reduced to the divalent state, europium exhibits chemical properties similar to the alkaline-earth elements and can be selectively precipitated as a sulfate, for example. This process is highly selective and allows production of high purity europium fromlow europium content solutions (see Calcium compounds Strontiumand strontium compounds). 

Divalent manganese compounds are stable in acidic solutions but are readily oxidized under alkaline conditions. Most soluble forms of manganese that occur in nature are of the divalent state. Manganese(Il) compounds are characteristically pink to colorless, with the exception of MnO and MnS which are green, and Mn(OH)2, which is white. The physical properties of selected manganese(Il) compounds are given in Table 6. 

Electrolytic (anodic) etching of siUcon occurs in HE solutions (5). Using concentrated HE, the siUcon is dissolved in the divalent state ... 

Silver sulfide, when pure, conducts electricity like a metal of high specific resistance, yet it has a zero temperature coefficient. This metallic conduction is beheved to result from a few silver ions existing in the divalent state, and thus providing free electrons to transport current. The use of silver sulfide as a soHd electrolyte in batteries has been described (57). 

The only oxide formed by any of these metals in the divalent state is CoO this is prepared as an olive-green powder by strongly heating the metal in air or steam, or alternatively by heating... 

Also in the divalent state, Pd and Pt show the class-b characteristic of preferring CN and ligands with nitrogen or heavy donor atoms rather than oxygen or fluorine. Platinum(IV) by contrast is more nearly class-a in character and is frequently reduced to Pt by P- and Aj-donor ligands. The organometallic chemistry of these metals is rich and varied and that involving unsaturated hydrocarbons is the most familiar of its type. 

The stabilizing effeets of half, and eompletely, filled shells ean be similarly invoked to explain the oeeurrenee of the divalent state in Eu"(4f ) and Yb (4f " ) while these, and the other known divalent ions are of just those elements whieh oeeupy elevated positions on the /a plot (Fig. 30.3). 

On heating with sulphur, MS2 result. PtS2 has the 6-coordinate Cdl2 structure whereas PtS2 is Pd2+(S2 ) in a distorted pyrite structure (4-coordinate PdPd—S 2.30 A) confirming the preference for the divalent state for... 

Most work on platinum involves complexes in the divalent state. Malatesta and Bonati report no platinum(O) or platinum(IV) species. The lack of... 

Thermal reduction at 623 K by means of CO is a common method of producing reduced and catalytically active chromium centers. In this case the induction period in the successive ethylene polymerization is replaced by a very short delay consistent with initial adsorption of ethylene on reduce chromium centers and formation of active precursors. In the CO-reduced catalyst, CO2 in the gas phase is the only product and chromium is found to have an average oxidation number just above 2 [4,7,44,65,66], comprised of mainly Cr(II) and very small amount of Cr(III) species (presumably as Q -Cr203 [66]). Fubini et al. [47] reported that reduction in CO at 623 K of a diluted Cr(VI)/Si02 sample (1 wt. % Cr) yields 98% of the silica-supported chromium in the +2 oxidation state, as determined from oxygen uptake measurements. The remaining 2 wt. % of the metal was proposed to be clustered in a-chromia-like particles. As the oxidation product (CO2) is not adsorbed on the surface and CO is fully desorbed from Cr(II) at 623 K (reduction temperature), the resulting catalyst acquires a model character in fact, the siliceous part of the surface is the same of pure silica treated at the same temperature and the anchored chromium is all in the divalent state. 

Positive Eu anomaly is observed for hydrothermal solution issuing from the hydrothermal vent on the seawater at East Pacific Rise (Bence, 1983 Michard et al., 1983 Michard and AlbarMe, 1986). Guichard et al. (1979) have shown that the continental hydrothermal barites have a positive Eu anomaly, indicating a relatively reduced environment. Graf (1977) has shown that massive sulfide deposits and associated rocks from the Bathurst-Newcastle district. New Brunswick have positive Eu anomalies. These data are compatible with positive Eu anomaly of altered basaltic rocks, ferruginous chert and Kuroko ores in Kuroko mine area having positive Eu anomaly and strongly support that Eu is present as divalent state in hydrothermal solution responsible for the hydrothermal alteration and Kuroko mineralization. 

The 4 g of iron in the human body is normally com-partmented into its functional locations in the haem- and non-haem-containing, and iron-binding proteins and enzymes (Fig. 3.5). The majority (65%) of the iron is in the divalent state in haemoglobin and myoglobin, which are involved in the transport and storage of oxygen in erythrocytes and myocytes, respectively. The remainder is distributed between storage sites, predominantly in the... 

Several copper minerals, containing copper in the divalent state, are completely soluble in sulfuric acid according to the following reactions ... 

After the loss of potential control, the Pb UPD layer may react with residual electrolytic solution to generate H2 and the Pb may be oxidized to the divalent state yielding a layer of PbO, Pb(0H)2 or PbF2. This is more likely to occur with UPD of Pb on Ag than for example on Au since the UPD potentials are more cathodic on Ag. Thus, for AEp = 0.15 V (see Figure 2a) and E°(Pb/PbF2) — -0.344 V in the reaction ... 

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