Iron 3 2+ aquation, cation effects

The addition of potassium, caesium, or tetra-alkylammonium (alkyl = methyl, ethyl, or n-butyl) salts has a marked effect on the rate of aquation of the tris-(5-nitro-l,10-phenanthroline)iron(n) cation. For a given concentration of added salt,... 

York and New England are devoid of fish due to the effects of acid rain. Indirect effects of the low pH values associated with acid rain also affect organisms. As noted in Table 13.1, one of the properties of an acid is the ability to dissolve certain metals. This has a profound effect on soil subjected to acid rain. Acid rain can mobilize metal ions such as aluminum, iron, and manganese in the basin surrounding a lake. This not only depletes the soil of these cations disrupting nutrient uptake in plants, but also introduces toxic metals into the aquatic system. 

The use of activation volumes in the diagnosis of mechanism has continued to provide much valuable information. Activation volumes for substitution at octahedral complexes have formed the subject of a well-referenced review,in which the importance both of intrinsic and of solvation contributions is recognized. The topics of most relevance to this chapter include isomerization and racemization reactions of cobalt(III) complexes, aquation of cobalt(III) and of iron(II) complexes, and base hydrolysis of cobalt(III) complexes. Merbach s continuing investigations into the effects of pressure on rates of solvent exchange at 2-h and 3+ transition metal cations, while not being always strictly... 

Kinetics of aquation of iron(n) complexes of 2,2 -bipyridyl, 1,10-phenan-throline, and their substituted derivatives have been much studied in water, less so in mixed aqueous solvents. Whereas the rate of aquation of [Fe(4,7-diPh-phen)3] + in acidic aqueous solution is approximately independent of the nature of the acid added, solutions of this complex in methanol solvolyse at rates which depend markedly on the nature of the acid added. A similar phenomenon has been observed for the aquation of [Fe(phen)a] +, [Fe(5-NOa-phen)3] +, and [Fe(4,7-diMe-phen)a] + in dioxan-water mixtures. These effects have been variously ascribed to the different strengths of the various acids i and to ion-pair formation. It is interesting that the rates of aquation of the iron(n) complexes in aqueous dioxan decrease as the concentration of acid increases when the acid added is perchloric or sulphuric. As ion pairs between complex cations and simple anions are generally more reactive than the free complexes, the observed rate trend is ascribed here, as in a similar situation involving the complexes [M(NH3)6(NOa)] +, with M = Rh or Ir, to the decrease in water activity on adding electrolytes. ... 

The kinetics of aquation of cobalt(III) or iron(III) complexes having hydrophobic ligands are usually affected by the presence of sulfonate anions. This effect has been attributed to hydrophobic interactions between the complex cations and the sulfonate anions. A recent paper discusses electrostatic and hydrophobic interactions in ion association between a series of tripositive complex ions and sulfonate anions. Ion association constants were determined at 25 °C by means of conductivity measurements of aqueous mixed electrolyte solutions at an ionic strength of 0.01 mol dm Some specific interactions in addition to the electrostatic ones were found to play a role in the ion associations of S04 with [Co(NH3)6] " and [Cr(en)3], in those of QHsSO and - 5114(803)2 with [Co(phen)3] and [Co(bipy)3] . 

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