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Rates of solvolysis of complex ions [Co(3Rpy).&lzlf with R = Me and Et have been determined in mixtures of water with t-butyl alcohol over a range of temperatures. Extrema found in the enthalpy AH* and entropy AS* of activation are correlated with the physical properties of the solvent mixtures which are influenced by changes in the solvent structure and these extrema are compared with those found for the solvolysis of related complexes in water + alcohol mixtures. Isokinetic plots over wide ranges of AH* and AS* are compared for the solvolysis of Co"' complexed to a variety of ligands. The application of a free energy cycle shows that the emergent cobalt (111) cation in the transition state becomes increasingly stabilized in water-rich mixtures relative to the cobalt (111) cation in the initial state as the mol fraction of t-butyl alcohol increases.

Rates of solvolysis of ions [Co(3Rpy),Cl2]+ with R = Me and Et have been measured over a range of temperatures for a series of water-rich water + methanol mixtures to investigate the effect of changes in solvent structure on the solvolysis of complexes presenting a largely hydrophobic surface to the solvent. The variation of the enthalpies and entropies of activation with solvent composition has been determined. A free energy cycle relating the free energy of activation in water to that in water + methanol is applied using free energies of transfer of individual ionic species from water into water + methanol. Data for the free energy of transfer of chloride ions AG:(Cl-) from both the spectrophotometric solvent sorting method and the TATB method for separating AG:(salt) into AG:(i) for individual ions are used: irrespective of the source of AGF(C1-1, in general, -AGP(Co(Rpy),C12+) > -AGP(Co(Rpy),Cl,'), where Rpy = py, 4Mepy, 4Etpy, 3Etpy, and 3Mepy, showing that changes in solvent structure in water-rich water + methanol mixtures generally stabilize the cation in the transition state more than the cation in the initial state for this type of complex ion. A similar result is found when the free energy cycle is applied to the solvolysis of the dichloro (2,2',2"-triaminotriethy1amine)cobaltW) ion. The introduction of a Me or E t group on the pyridine ring i n Consequently, if R, is a halide ion, the influence of change in solvent on the solvolysis can be interpreted in terms of the influence of changes in solvation (including changes in the structure of the solvent medium) on the ion [CoN,R,halide]"+ in the initial state and [ C O N~R~] ( "~~)~ and the halide ion in the transition state. An initial survey of the kinetic data available showed [4] that the linear relation of log (rate constant) with the reciprocal

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The free energy of transfer of the proton between water and water-rich mixtures of water and tetrahydrofuran (THF), AG:(H+), has been found by examining spectrophotometrically the redistribution of solvent molecules around the aqua-proton after the latter charged sphere has been transferred into the mixture. Values for AG,"(HX) calculated from electrochemical data are combined with the new AG,"(H+) to produce AG,"(X-) for the transfer of halide ions and of OHfrom water into water-THF mixtures. These AG,"(X-) are then used with values for AG,"(MX) derived from electrochemical and vapour-pressure measurements to give values for AG,"(M+) for alkali-metal ions and for ButN+ ions. pK values for two carboxylic acids and for a range of anilinium cations in water-THF mixtures are combined with AG:(H+) to produce AG: & the free energy of transfer from water into water-THF of the charge on the carboxylate anion or the anilinium cation with the effect of transferring the molecular bulk of the ion removed.The spectrophotometric solvent sorting m e t h ~d l -~ for the determination of the free energy of transfer of the proton from water into water

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Rates of solvolysis of complex ions [C0(3Rpy)~Cl~]+ with R = Me and Et have been determined in mixtures of water with the hydrophobic co-solvent propan-2-01 for a range of temperatures. The variations of the enthalpies and entropies of activation with the solvent composition have been correlated with the physical properties of the solvent and it has been shown that the linear plot found for AH* against AS* in water + propan-2-01 is coincident with that found for water + methanol mixtures. A free energy cycle has been applied to the dissociative-type process of initial state (C"') going to the transition state (M("+')'. . . . . It is concluded that, using values for AGp(Cl-) from either source, the stabilizing influence of changes in solvent structure is greater on the cation in the transition state than on the cation in the initial state for the solvolyses of complexes [ C~( R p y )~C l~+ l and [CoenzLCl]"'.As part of our continuing investigation of the kinetics of hydrolytic reactions involving inorganic complexes with varying hydrocarbon content on the surface of their molecules in mixtures of water with co-solvents of varying hydrophilic [l] Propan-2-01 has been chosen as the co-solvent as properties of its mixtures with water, such as the deviation of the extremum in the excess enthalpy of