Oxides and Related Anions

Ru04 reacts with pyridine to form Ru03(py), probably a dimer Py2(0)2Ru(/i-0)2Ru(0)2Py2, an aerobically assisted oxidant [48c]. 

Ru02 can be made by high-temperature oxidation of ruthenium. It has the rutile structure (Ru-O 1.942 A and 1.984 A) and forms blue-black crystals [49b], 

Recently Ru03 has been made as a brown solid by photolysis  

In matrices, Ru02 is bent (149°) while Ru03 is trigonal planar. 

Copper-coloured 0s02 also has the rutile structure it can be made from the metal and NO at 650°C. 

In matrices, RUO2 is bent (149 ) while RUO3 is trigonal planar. 

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Stibine Oxides and Related Compounds. Both aUphatic and aromatic stibine oxides, R SbO, or their hydrates, R3Sb(OH)2, are known. Thus both dihydroxotrimethylantimony [19727-41-4], C3H2202Sb, and trimethyl stibine oxide [19727-40-3], C H OSb, have been prepared. The former maybe readily obtained by passing an aqueous solution of dichi orotrimethyl antimony [13059-67-1], C3H2Cl2 > through an anionic-exchange resin (151). 

To conclude this chapter, we look back at the earlier literature in hopes of widening both the potential deposition methods and the materials that can be deposited. As well as oxides and related compounds, other anions are considered. The resulting compounds do not necessarily fall under the common heading of semiconductors, but they are relevant in the hope of expanding the scope of chemical deposition. 

Apparently the problems with slow equilibration can be avoided by increasing the equilibration time, but it is not always the case. For example, the presence of complexing anions often enhances dissolution of metal oxides and related adsorbents. This results in the following kinetic pattern the uptake as a function of time rises, peaks and then declines. In order to account for this effect, the declining segment was extrapolated to / = 0 [21], and the intersection with the axis of ordinates was interpreted as uptake corrected for dissolution of the adsorbent. Anyway, negligible dissolution of the adsorbent is a substantial advantage of experiments with relatively short equilibration times. 

Temperature the results compiled in Tables 4.1-4.6 were obtained at different temperatures, and in some studies the temperature was not controlled. The results reported in Table 3.11 and Fig. 3.104 indicate that the PZC of oxides and related materials shifts to low pH when the temperature increases (with a few exceptions). Most surfaces carry more negative charge at elevated temperature (at given pH), and this creates favorable conditions for adsorption of cations and unfavorable conditions for adsorption of anions. Therefore elevated temperature would enhance uptake of cations, and low temperature would enhance uptake of anions at constant pH, if the electrostatic interaction was the only factor. On the other hand, the rate of chemical reactions and diffusion is enhanced at elevated temperatures. Thus, the kinetic and electrostatic effect on cation adsorption add up and the uptake increases with temperature. With anions these effects act in opposite directions the uptake increases with temperature when the kinetic factor prevails the uptake decreases with temperature when the electrostatic factor prevails, finally the both effects can completely cancel out. 

Affinity series for various hydrous oxides are compiled in [3089]. The compilation of affinity series in [3168] also includes Agl and Hg. A review of affinity series of metal cations is presented in [2981]. Increasing affinity in a series from Li to Cs is reported for materials with PZCs at pH < 4, and decreasing affinity in a series from Li to Cs is reported for materials with PZCs at pH > 5. An analytical expression for stability constants of =SOMe and =SOH2X complexes (TLM) as a function of the dielectric constant of the solid and the ionic radii was proposed in [3169]. The results for common oxides and common anions and cations are tabulated. Examples of ion specihcity in different phenomena, not directly related to surface charging, are presented in [3170]. 

Reference has been made to the observation that both anionic and cationic species in the environment can influence the anodic polarization of active-passive types of metals and alloys. Specific examples have related to the effect of pH as it influences the stability and potential range of formation of oxide and related corrosion product films. The effect of pH, however, cannot be treated, even with single chemical species, independent of the accompanying anions. For example, chloride, sulfate, phosphate, and nitrate ions accompanying acids based on these ionic species will influence both the kinetics and thermodynamics of metal dissolution in addition to the effect of pH. Major effects may result if the anion either enhances or prevents formation of protective corrosion product films, or if an anion, both thermodynamically and kinetically, is an effective oxidizing species (easily reduced), then large changes in the measured anodic polarization curve will be observed. 

Carbonates, Thiocarbonates, and Related Anions, The syntheses of carbonates, hydroxide carbonates, and oxide carbonates have been reported. Those factors which influence the crystallization of rare-earth carbonates have been investigated the carbonates were precipitated at various temperatures from aqueous solutions by using sodium carbonate (20—80 C), sodium bicarbonate (20—80 °C), trichloroacetic acid (40—120 °C), and urea (50—150 °C) as precipitants. The carbonates so formed were characterized by chemical analysis and A"-ray powder diffraction techniques. It was found that they could be classified into several phases (Table 19) according to the ionic radii... 

There is evidence that sequestration rates of certain zeolites, such as zeolite A, can be enhanced by incorporating Af-tetradecyldimethylamine oxide and related species. The increased sequestration imparted by the amine oxide synergy is claimed to make zeolite A more suitable for use as a detergent builder in anionic surfactant-based formulas [55]. 

Oxides commonly studied as catalytic materials belong to the structural classes of corundum, rocksalt, wurtzite, spinel, perovskite, rutile, and layer structure. These structures are commonly reported for oxides prepared by normal methods under mild conditions [1,5]. Many transition metal ions possess multiple stable oxidation states. The easy oxidation and reduction (redox property), and the existence of cations of different oxidation states in the intermediate oxides have been thought to be important factors for these oxides to possess desirable properties in selective oxidation and related reactions. In general terms, metal oxides are made up of metallic cations and oxygen anions. The ionicity of the lattice, which is often less than that predicted by formal oxidation states, results in the presence of charged adsorbate species and the common heterolytic dissociative adsorption of molecules (i.e., a molecule AB is adsorbed as A+ and B ). Surface exposed cations and anions form acidic and basic sites as well as acid-base pair sites [1]. The fact that the cations often have a number of commonly obtainable oxidation states has resulted in the ability of the oxides to undergo oxidation and reduction, and the possibility of the presence of rather high densities of cationic and anionic vacancies. Some of these aspects are discussed in this chapter. In particular, the participation of redox sites in oxidation and ammoxidation reactions and the role of redox sites in various oxides that are currently pursued in the literature are presented with relevant references. 

The first closo metaHaborane complexes prepared (159) were the nickelaboranes [< /(9j 0-( q -C H )Ni(B22H22)] and closo-l]l- r]-Q ]) -l]l-53i] pri Q [55266-88-1] (Fig. 13). These species are equivalent to closo-C ]]ri ][ i closo-Q, p5 2 by tbe electron-counting formaUsm. The mixed bimetallic anion [ /(9j (9-(Tj -C H )2CoNi(B2QH2Q)] and other related species were reported later (160). These metallaboranes display remarkable hydrolytic, oxidative, and thermal stabiUty. 

Figure 17.26 Structures of chlorine oxide fluorides and related cations and anions.

The usual oxidizing agents transfer oxygen (or halogens and related species with subsequent hydrolysis) stepwise to the sulfur of thioethers Rates of step A compared with those of step B are faster with electrophilic oxidation agents (peroxy acids) inversely, rates of step B compared with those of step A are faster with nucleophilic oxidation agents (peroxy anions)339-341. 

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