Tetrahedral oxidations

Unlike sulfoxides, which exist primarily as the tetrahedral oxide, both selenoxides and telluroxides add water to give dihydroxy selenanes and telluranes, respectively, which have trigonal bipyramidal structures with two hydroxyl groups as the axial ligands. The hydration step is reversible as shown in Fig. Diphenylselen-... 

Unlike traditional porous zeolites, whose pores are confined by tetrahedral oxide skeletons, and thus, are difficult to tune, the pores within PCPs can be systematically... 

Cr-HMS exhibits PL bands at --550-570 ran, upon excitation of the absorption (excitation) bands at 250, 360, and 480 nm. These PL and absorption bands are similar to those obtained earlier with well-defined, highly dispersed chromium oxides grafted onto PVG or silica (Anpo et al., 1982). They can be assigned to CT processes in tetrahedral oxide moieties involving electron transfer from O2 to Cr6+ and the reverse radiative decay, respectively. 

Yin JS, Wang ZL (1997) Ordered self-assembling of tetrahedral oxide nanocrystals. Phys Rev Letters 79 2570-2573... 

The simple ionic theory predicts transition from octahedral to tetrahedral oxide environment at r 0.58 A, assuming r — = 1.40 A. 

Experimental spectra of two structurally well-defined model systems illustrate this difference (i). The upper spectrum of Figure 2 is that of a single crystal of ferric ammonium sulfate which contains Fe HoO)e the lower spectrum is that of an Fe -doped sample of orthoclase feldspar. In this sample, Fe ions replace AF in a certain percentage of tetrahedral oxide donor sites. The two spectra show very clearly that the two lowest bands, Ai Ti( G) and Ai T2( G), are substantially lower in energy in the [Fe(III)06]oct case. These spectra were selected because four LF bands are resolved in each case. The third band is fairly sharp in each spectrum and is assigned to the transition which does not require orbital promotion, Ai Ai, E( G). The fourth band in each case is assigned Ai T2( D). 

NO was used as an oxidant. Methane conversion and methanol selectivity reached 6% and 88%, respectively, after UV irradiation for 3 h. As shown in Figure 18.9, the yield of methanol increases with an increase in the V content up to 0.6 wt%, and then decreases with a further increase in the V content. The observed good correspondence between the yield of methanol and the intensity of the photoluminescence indicates that the isolated tetrahedral oxide species act as active sites for the photocatalytic oxidation of methane with NO into methanol. 

Other rare earth elements ako found activity in these catalysts. The catalytic activity of cerium-incorporated cage-type mesoporous KlT-6 materials in oxidation of cyclohexene was explained as effect of from the framework with tetrahedral oxidic coordination [27]. When H2O2 is chemisorbed, only the distant oxygen is activated, by which cyclohexane could be oxidized by insertion of oxygen across the C—H bond, as illustrated in Scheme 21.1. Hence, cyclohexanol is the principal product in thk oxidation. Recyclability of the catalyst without leaching of cerium in the presence of the solvent was an important characteristic of this catalyst. Acetic acid as a solvent led to better results compared to either acetone or methanol. 

Manganates V f), [MnOJ", permanganates. Dark purple tetrahedral anion (electrolyte oxidation of [Mn04]. Powerful oxidizing agent... 

The concept of oxidation states is best applied only to germanium, tin and lead, for the chemistry of carbon and silicon is almost wholly defined in terms of covalency with the carbon and silicon atoms sharing all their four outer quantum level electrons. These are often tetrahedrally arranged around the central atom. There are compounds of carbon in which the valency appears to be less than... 

The chromates of the alkali metals and of magnesium and calcium are soluble in water the other chromates are insoluble. The chromate ion is yellow, but some insoluble chromates are red (for example silver chromate, Ag2Cr04). Chromates are often isomorph-ous with sulphates, which suggests that the chromate ion, CrO has a tetrahedral structure similar to that of the sulphate ion, SO4 Chromates may be prepared by oxidising chromium(III) salts the oxidation can be carried out by fusion with sodium peroxide, or by adding sodium peroxide to a solution of the chromium(IIl) salt. The use of sodium peroxide ensures an alkaline solution otherwise, under acid conditions, the chromate ion is converted into the orange-coloured dichromate ion ... 

Incorporating an oxygen atom into a three membered nng requires its bond angle to be seriously distorted from the normal tetrahedral value In ethylene oxide for exam pie the bond angle at oxygen is 61 5°... 

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