We report solubilities of a number of cobalt(III) and chromium(III) complex salts in methanol-water mixtures. From these, and published solubilities of salts of other complexes of these metals, we have calculated transfer chemical potentials from water into aqueous methanol for a variety of cationic and anionic complexes of cobalt(III) and chromium(III), using the assumption δmμ⊖(Ph4As+) + δmμ⊖(BPh
 4
 −
 ). The established trends are discussed in terms of electrostatic factors and of the hydrophilicity or hydrophobicity of the ligands present. The effects of single ion assumptions on conclusions of initial state-transition state analyses of solvent effects on reactivity are assessed with particular reference to aquation of thetrans-[Co(en)2Cl2]+ andtrans-[Co(py)4Cl2]+ cations.

Transfer Chemical Potentials for Cobalt(III) and Chromium(III) Complexes from Water into Aqueous Methanol; their Relevance to Reactivity Trends for Cobalt(III)-Chloride Aquation

Kinetics of oxidation of ferrocene by tris-1,10-phenanthrolinecobalt(III) in t-butyl alcoholwater and acetonewater mixtures

Enthalpies of solution (298 K) are reported for NiCl2 · 6H2O, CoCl2 · 6H2O, and FeCl2 · 4H2O in aqueous methanol (0–40% methanol) and for NiCl2 · 6H2O, 2,2′-bipyridyl, and water in aqueous dimethyl sulphoxide (0–60% DMSO). Solubilities (298 K) of 2,2′-bipyridyl are reported for aqueous dimethyl sulphoxide (0–60% DMSO). From these, from appropriate published thermodynamic data, and from published rate constants and activation enthalpies, we have analysed solvent effects on reactivities (μ and H) into initial state and transition state contributions (the latter are in fact composite ion-association and interchange quantities). In all systems examined the observed kinetic trends represent small differences between large and almost identical solvent effects on the respective initial and transition states.

The reaction of nickel(II) with 2,2′-bipyridyl in methanol- and in dimethyl sulphoxide-water mixtures: Solvent effects on reactivity

The coverage and arrangement of this chapter are very much the same as in previous volumes of this series. Although activity in some areas has diminished, it has undergone a comparable increase in others. Thus classical kinetic studies of substitution at, e.g., rhodium(III) and platinum(IV) centers have been rather rare during the period covered by this report. On the other hand, there has been increasing activity in substitution at the lower oxidation states of osmium, thanks largely to Taube’s novel studies, at ruthenium(II), largely in a photochemical context, and at technetium in various oxidation states, wholly in relation to the medical uses of a variety of its complexes. Perhaps the biggest increase in activity in the field defined by the title of this chapter has been in studies of systems in which ligand engineering has resulted in the dramatic slowing of substitution at normally labile centers. Such studies have often been impelled by the needs of radiotherapy, where a nucleus with specific radiochemical properties is required to be delivered to the site of action. An appropriate ligand is needed to transport the nucleus to its intended site, and of course it is necessary that this ligand shall not be lost en route if the metal ion happens to be substitution-labile. Uncharacteristically inert behavior of such centers as copper(II) and lanthanides(III) will be discussed in the following paragraphs, before the customary systematic treatment of the usual set of inert elements.

Substitution Reactions of Inert-Metal Complexes—Coordination Numbers 6 and Above: Other Inert Centers

Activation enthalpies have been determined for aquation of thetris(1,10-phenanthroline)iron(II) cation and for its reaction with hydroxide in 20, 40, and 80% (by volume) methanol, and for its reaction with cyanide in 20 and 40% methanol. Enthalpies of solution of the chloride salt of this cation, and of potassium cyanide, have been determined in the water-methanol mixtures. From these results and ancillary thermodynamic data we have dissected the variations of activation enthalpies for these three substitution reactions with solvent composition into their initial state and transition state components. In the water-rich mixtures (0 to 40% methanol) initial and transition state solvation effects are similar and dominated by the ligands, but in the reaction with hydroxide in 80% methanol there is a striking difference between initial and transition state behaviour.

Initial state and transition state contributions to solvent effects on activation enthalpies for substitution reactions of tris(1,10-phenanthroline)iron(II) in aqueous methanol

John P. McCann

Papers

Initial state and transition state contributions to solvent effects on activation enthalpies for substitution reactions of tris(1,10-phenanthroline)iron(II) in aqueous methanol