Complex anions formation

The existence of such C H O intermediate anion collision complex had previously been suggested by Comer and Schulz [254], who measured the energies of electrons emitted during gas-phase collisions of 0 with C2H4. Further evidence for a complex anion formation and reactive scattering in the gas phase can be seen in the studies of Parkes [255] and Lindinger et al. [256]. 

Evidence foi the anionic complex PuCP is the precipitation of complex halides such as Cs2PuClg from concentrated HCl (aq). The ability of Pu(IV) to form stable nitrate complexes provides the basis for the Purex and ion-exchange (qv) process used in the chemical processing of Pu (107). Pu(VI) is similar to Pu(IV) in its abihty to form complex ions. Detailed reviews of complex ion formation by aqueous plutonium are available (23,94,105). 

After preparing a homogeneous solution of the precursors, powder precipitation is accompHshed through the addition of at least one complexing ion. For PLZT, frequently OH in the form of ammonium hydroxide is added as the complexing anion, which results in the formation of an amorphous, insoluble PLZT-hydroxide. Other complexing species that are commonly used are carbonate and oxalate anions. CO2 gas is used to form carbonates. Irrespective of the complexing anion, the precipitated powders are eventually converted to the desired crystalline oxide phase by low temperature heat treatment. 

All the tetrahalides, but especially the chlorides and bromides, behave as Lewis acids dissolving in polar solvents to give rise to series of addition compounds they also form complex anions with halides. They are all hygroscopic and hydrolysis follows the same pattern as complex formation, with the chlorides and bromides being more vulnerable than the fluorides and iodides. TiCU fumes in and is completely hydrolysed by... 

If the nucleophilicity of the anion is decreased, then an increase of its stability proceeds the excessive olefine can compete with the anion as a donor for the carbenium ion, and therefore the formation of chain molecules can be induced. The increase of stability named above is made possible by specific interactions with the solvent as well as complex formations with a suitable acceptor 112). Especially suitable acceptors are Lewis acids. These acids have a double function during cationic polymerizations in an environment which is not entirely water-free. They react with the remaining water to build a complex acid, which due to its increased acidity can form the important first monomer cation by protonation of the monomer. The Lewis acids stabilize the strong nucleophilic anion OH by forming the complex anion (MtXn(OH))- so that the chain propagation dominates rather than the chain termination. 

The interaction of a complex anion SbY5Z with excessive Lewis acid SbX5 leads to the formation of a ligand-bridged (conjugated 1)) anion (see part 4.2.2) according to... 

Table 18 summarizes the interaction energies between the anions SbYsZ and the Lewis acids SbX5, In general, the formation of a conjugated anion proceeds exothermically (—0.7. .. —1.9 eV). This energy is clearly smaller than those for the interaction between a Lewis acid SbX5 and a halide ion 7T (—4.1. .. —6.3 eV). The interaction of Lewis acids with complex anions decreases in the rows respectively ... 

In the case of the rhenium aqua-ion [Re(OH2)3(CO)3]+ (33b) the question has been posed whether complex-anion can be considered to be a Bronsted acid. Titrations with hydroxide in water yielded a pKa value of 7.55 which is exceptionally low for a +1 cation. After the deprotonation of one coordinated water molecule, polymer formation over (/r-OH) bridges was initiated and the two compounds [Re3(/T3-OH)(/T-OH)3(CO)9r (35) and [Re2(/i-OH)3(CO)6] were (36) isolated and structurally characterized (Scheme 6). 

The process of chelation was discussed in Chapter 3. To form uncharged chelates which can readily be extracted into organic solvents the reagent must behave as a weak acid whose anion can participate in charge neutralization and contain hydrophobic groups to reduce the aqueous solubility of the complex. The formation and extraction of the neutral chelate is best considered stepwise as several equilibria are... 

The complex anion [Pt(S-Me2SO)Cl3] undergoes an internal redox reaction in acidic media, and evidence for the formation of Pt(IV) species and Me2S has been presented (466). This may be an explanation for the deoxygenation of (CH2)4SO previously mentioned (164). The oxidation of Pt(II) to Pt(IV) with concomitant reduction of Me2SO to Me2S has been accomplished using hydrochloric acid (357), as shown in Eq. (28). 

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