Anions, Effect

Anion effects have been observed especially in relation to dissolution of the cation complexes in media of low polarity. Soft organic and inorganic anions (phenates, thiocyanate, permanganate etc) generally allow ready dissolution the pier ate anion has been much used (62, 66). The interaction between the anion and the complexed cation may affect the stability of the complex. Ion pairing may occur when the anion can contact the complexed cation, as in the case of macrocyclic complexes, where approach of the anion from top and bottom is possible. This is observed in the RbNCS complex of IS, but not in its NaNCS complex, as shown by the crystal structure data (100). With bromide as anion both a complexed ion pair and a complexed sodium cation are found in the solid state for (15, NaBr) (118). 

---

Table 3.1-2 [EMIM]X salts and melting points, illustrating anion effects.

If the cation has been unchanged, its ability to act as a hydrogen-bond donor has been unchanged, so why is an effect seen at all I propose that there is competition between the anion and the Reichardt s dye solute for the proton. Thus, the values of the ionic liquids are controlled by the ability of the liquid to act as a hydrogen bond donor (cation effect) moderated by its hydrogen bond acceptor ability (anion effect). This may be described in terms of two competing equilibria. The cation can hydrogen bond to the anion [Equation (3.5-2)] ... 

Comparison of Ca3(POi)2, Ca(C204), and Mg3(P04)2. The effects of cation and anion composites were tested by comparing the dissolution of Ca3(P04)2, Ca(C204), andMg3(P04)2 at pH 7 (Table 10). The dissolution of Ca3(P04)2 is achieved more effectively with X than with EDTA. However, when the anion is oxalate, the dissolution of Ca2+ is drastically reduced with X. EDTA can dissolve Ga(C204) to the same extent as Ca3(P04)2, i.e. the anion effect is insignificant. A better separation of Ca2+ from oxalate anion may be achieved by EDTA. 

NOTE It is also apparent that the ferric ion (Fe3+) should chelate most readily. In practice, however, under strongly alkaline conditions, the preferred reaction is to instantaneously form ferrous hydroxide and then to slowly revert to ferric hydroxide (competing anion effect). 

NOTE If the BW contains phosphate, the preferred reaction is for calcium to precipitate as hydroxyapatite, rather than to chelate with EDTA or NTA (a further competing anion effect). Consequently, there would seem to be no valid reason to produce combined phosphate-chelant programs, with the chelant acting as a reserve against unforeseen hardness incursions caused by a softener leakage, or other source. In practice, the chelant acts to solubilize existing deposits, producing a very clean boiler. 

NOTE Although control over transported iron is critical in larger power boilers, as discussed earlier, control by the chelation of ferric iron is not possible (because of the competing anion effect). Consequently, Fe203 and Fef04 are essentially unaffected by chelants. However, it is well known that where an iron chelate (chelonate) is formed, it is stable and will not be destroyed by hydrolysis at high temperature. 

If the alkalinity is too low, iron corrosion may take place. If the alkalinity is too high, there is a further competing anion effect, with magnesium precipitated as Mg(OH)2, rather than chelated. 

Since the rate does not display an inverse dependence on Hg(II) concentration, the oxidation of Hg atoms, in equilibrium with mercury(l) and mercury(II), can be discounted, although Hg atoms are kinetically important in the reduction of thallium(IIl) by mercury(I) . It seems likely that the acid-dependent path (A ) involves CoOH. Anion effects were not investigated. 

These last examples illustrate the effecte of heavy cations on anionic stability. The opposite case of an anionic effect is also possible. Thus diazonium salts are hardly stable but not dangerous when the anion is a chloride ion, whereas they become dangerous when the anion is a sulphide or carboxylate. 

Housmans THM, Koper MTM. 2005b. CO oxidation on stepped Rh[n(lll) x (111)] single-crystal electrodes Anion effects on CO surface mobility. Electrochem Commun 7 581-588. 

Markovic NM, Lucas CA, Rodes A, Stamenkovic V, Ross PN. 2002. Surface electrochemistry of CO on Pt(lll) Anion effects. Surf Sci 499 L149-L158. 

Anionic effects were observed by FT-IR-ATR spectrometry with a membrane containing not ionophore 2 but a different kind of ionophore, ETH 129 [13]. When the lipophilic counteranion, SCN, was used for the primary ion solutions, the spectra from both the complexed cation and corresponding counteranion were seen, of which the stoichiometric ratio was nearly equal to that of ETH 129 complex-SCN salt at relatively high concentrations of the primary ion solutions. With KTpCIPB in the membrane. 

The true role of incorporation of anions in the formation of anodic alumina is being intensively discussed. Baker and Pearson183 have considered the anion effect in modifying the structure of anodic oxides to be due to the coordinative ability of anions to replace alumina tetrahedra in the body of the oxides. Dorsey184,185 has postulated that in porous oxides, anions stabilize the network of alumina tetrahedra and octahedra. 

In proposed mechanism I, the loss of water from the complex is the rate-determining step, but removal of water from the coordination sphere of the metal ion should be independent of the nature of the anion that is not part of the coordination sphere of the metal ion. On the other hand, if mechanism II is correct, the entry of X into the coordination sphere of the metal would be dependent on the nature of the anion, because different anions would be expected to enter the coordination sphere at different rates. Because there is an observed anion effect, it was concluded that the anation reaction must be an Sn2 process. However, it is not clear how a process can be "second-order" when both the complex cation and the anion are parts of the same formula. As discussed in Chapter 8, it is not always appropriate to try to model reactions in solids by the same kinetic schemes that apply to reactions in solutions. 

Fig. 31.18 Anion effects on the enantioselective hydrogenation shown (adapted from [77]).

Cavity size and cation diameter 283 Spatial arrangement of binding sites 289 Additional binding sites 293 Electron density at the binding sites 299 Nitrogen and sulfur donor sites 302 Solvent effects 304 Anion effects 308... 

The anion effect on the extractability of salts from aqueous into organic solution ( ext) has been studied by several workers. It was found that the extractability increased with increasing hydrophobicity of the anion (Jawaid and Ingman, 1978). 

The influence of antimony at a level of 300 ppm in copper electrolysis is also significant. The morphologies of deposits made from a pure acid-copper sulfate electrolyte and from an identical solution to which the antimony was added are shown in Figures 5 and 6. There are many other combinations of impurities and electrolytes which exhibit this changing surface appearance and deposit orientation besides those selected as examples. Anion effects are also not uncommon, with the halogens often causing the more notable changes. 

The nature of the ternary species is unclear but the addition of perchlorate to the complex causes no detectable shift in the position of the peaks in the visible spectrum. This may indicate that the anion effect involves an outer-sphere association or it may involve a weak axial inner-sphere coordination. 

The existence of such anion effects also implies that, if one wishes to do temperature studies, one cannot simply sit at a constant ionic strength and obtain meaningful activation parameters, because the equilibrium constant involving the association with the anion will also change, of course, as one varies the temperature. Thus, it is necessary to resolve out each rate constant at each temperature and then do the temperature dependencies on individual rate constants. 

The mechanism proposed72 involves initial nucleophilic attack at the carbene carbon by the dithiocarbamate anion, effectively resulting in addition across the metal-carbon bond. Rearrangements of the dithiocarbamate ligands then form an V-allyldithiocarbamate species Complex 53 was isolated from the reaction mixture of 51 with the diethyldithiocarbamate and identified by X-ray crystallography. 

---