Ion replacements

In the presence of 18-crown-6, phthahmide ion replaces the 2-, 4-, and 6-fluonnes in perfluoropyndme, whereas only the 4-fluonne is replaced m the absence of the crown ether [77] (equation 40)... 

As one example, in thin films of Na or K salts of PS-based ionomers cast from a nonpolar solvent, THF, shear deformation is only present when the ion content is near to or above the critical ion content of about 6 mol% and the TEM scan of Fig. 3, for a sample of 8.2 mol% demonstrates this but, for a THF-cast sample of a divalent Ca-salt of an SPS ionomer, having only an ion content of 4.1 mol%, both shear deformation zones and crazes are developed upon tensile straining in contrast to only crazing for the monovalent K-salt. This is evident from the TEM scans of Fig. 5. For the Ca-salt, one sees both an unfibrillated shear deformation zone, and, within this zone, a typical fibrillated craze. The Ca-salt also develops a much more extended rubbery plateau region than Na or K salts in storage modulus versus temperature curves and this is another indication that a stronger and more stable ionic network is present when divalent ions replace monovalent ones. Still another indication that the presence of divalent counterions can enhance mechanical properties comes from... 

As the hydrogen ions replace alkali (R) ions a surface film forms which has properties different from the massive glass. This film swells, acting as a barrier to further diffusion of ions into, and out of, the surface, inhibiting further attack. If this layer dries out, the thin film gives characteristic irridescent interference colours. 

Here the number of ions remains unchanged only the smaller (NII4)+ ion replaces the initial larger ion. Although in Sec. 19 we discussed the... 

The mode of extraction in these oxonium systems may be illustrated by considering the ether extraction of iron(III) from strong hydrochloric acid solution. In the aqueous phase chloride ions replace the water molecules coordinated to the Fe3+ ion, yielding the tetrahedral FeCl ion. It is recognised that the hydrated hydronium ion, H30 + (H20)3 or HgO,, normally pairs with the complex halo-anions, but in the presence of the organic solvent, solvent molecules enter the aqueous phase and compete with water for positions in the solvation shell of the proton. On this basis the primary species extracted into the ether (R20) phase is considered to be [H30(R20)3, FeCl ] although aggregation of this species may occur in solvents of low dielectric constant. 

FIGURE 16.16 When potassium cyanide is added to a solution of iron(ll) sulfate, the cyanide ions replace the H.O ligands of the [Fe(H20), - + complex (left and produce a new complex, the hexacyanoferrate(ll) ion, Fe(CN)(l 4 (right). The blue color is due to the polymeric compound called Prussian blue, which forms from the cyanoferrate ion. 

Many complex ions, such as NH4+, N(CH3)4+, PtCle", Cr(H20)3+++, etc., are roughly spherical in shape, so that they may be treated as a first approximation as spherical. Crystal radii can then be derived for them from measured inter-atomic distances although, in general, on account of the lack of complete spherical symmetry radii obtained for a given ion from crystals with different structures may show some variation. Moreover, our treatment of the relative stabilities of different structures may also be applied to complex ion crystals thus the compounds K2SnCle, Ni(NH3)3Cl2 and [N(CH3)4]2PtCl3, for example, have the fluorite structure, with the monatomic ions replaced by complex ions and, as shown in Table XVII, their radius ratios fulfil the fluorite requirement. Doubtless in many cases, however, the crystal structure is determined by the shapes of the complex ions. 

As in dissolution, a chemical and structural change can occur from hydrolysis as the ions replaced by or OH may be of a different size so that the crystal structure is stressed and weakened. An example of this is the weathering of feldspar or goethite by H ... 

C04-0026. Cadmium ions are environmental pollutants found in mining waste, metal plating, water pipes, and industrial discharge. Cadmium ions replace zinc ions in biochemistry and cause kidney damage, high blood pressure, and brittle bones. Dissolved Cd " " impurities can be removed from a water sample... 

Reactions with clay minerals can neutralize both low-pH and high-pH solutions. Neutralization of acids occurs when hydrogen ions replace Al, Mg, and Fe. In alkaline solutions, neutralization is more complex and may involve cation exchange, clay dissolution, and reaction of cations with hydroxide ions to form new minerals called zeolites.39... 

The situation is more complex when several ions replace the sodium. In Bao.75Al11Oi7 25 containing 10 mol % Eu2+, the lanthanide ions occupy both BR and anti-BR sites. 

Titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy are two techniques which have seldom been applied to study reactions at the solid-liquid interface. In this paper, we describe these two techniques and their application to the investigation of salicylate ion adsorption in aqueous goethite (a-FeOOH) suspensions from pH 4 to 7. Evidence suggests that salicylate adsorbs on goethite by forming a chelate structure in which each salicylate ion replaces two hydroxyls attached to a single iron atom at the surface. 

Figure 5.9 The sodium ion/glucose transporter and sodium ion/ amino acid transporter. The biochemistry of the two processes is identical. To maintain electroneutral transport K ion replaces Na ion, via NaVK ATPase. The broader arrow indicates overall effect (i.e. unidirectional) transport.

Table 4.3 presents the relative rate constants of the chlorine-to-methoxy substitution in the nitrobenzene series (Epiotis 1973). The methoxide ion replaces chlorine in 4-chloro-3-methyl-nitrobenzene more rapidly than in 6-chloro-3-methylnitrobenzene (Table 4.3, entries 1 and 2). This... 

Oxidation of -hexane with Co AlPO-18 with 10% rather than 4% of the framework AP ions replaced with Co resulted in a dramatic enhancement in the formation of adipic acid [65]. It was argued that in these catalysts two Co ions are ideally separated by 7-8 A on the inner wall of the zeolite, allowing both methyl groups unfettered access to catalytically active sites. Furthermore, it was demonstrated that 1,6-hexanediol and 1,6-hexanedial served as precursors to the adipic acid. On the other hand, 1-hexanol, hexanoic acid, and hexanal, which were also formed in the reaction, did not serve as precursors for the adipic acid. It is tempting to suggest that the mono-oxidized hexane products were produced in regions of the zeolite where simultaneous access to two catalytically active sites was not possible. 

Fig. 2.2B The octahedral (O) sheet. The composition can be expressed as f(Mg3-x-YR xR y)02(OH)4ln. The dashed circles represent the apical oxygens of the underlying T sheet. These ions replace the hydroxyls in the octahedral sheet and are common to the T and O sheets. The cross-hatched circles represent the remaining hydroxyls. The circles with crosses represent hydroxyls at the upper portion of the octahedral sheet. The small circles represent magnesium ions.

Ferrisilicate zeolites wherein iron ions replace silicon in the lattice framework have potential as catalyst in various conversion processes. During the past decade ferrisilicate analogs of sodallte, MFI, M, MTT, EUO, MTW, FAU, BETA, MOR and LTL have been synthesised and characterised by various physicochemical techniques as well as catalytic reactions. After a review of the general synthesis procedures a list of criteria is presented to confirm the location of Fe in the zeolite framework. Examples are provided to illustrate the utility of the various characterisation techniques. 

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