Solvent exchange equation

Panagiotopoulos et al. [16] studied only a few ideal LJ mixtures, since their main objective was only to demonstrate the accuracy of the method. Murad et al. [17] have recently studied a wide range of ideal and nonideal LJ mixtures, and compared results obtained for osmotic pressure with the van t Hoff [17a] and other equations. Results for a wide range of other properties such as solvent exchange, chemical potentials and activity coefficients [18] were compared with the van der Waals 1 (vdWl) fluid approximation [19]. The vdWl theory replaces the mixture by one fictitious pure liquid with judiciously chosen potential parameters. It is defined for potentials with only two parameters, see Ref. 19. A summary of their most important conclusions include ... 

The definition of solvent exchange rates has sometimes led to misunderstandings in the literature. In this review kjs 1 (or fc2lsolvent]), sometimes also referred to as keJ s 1, is the rate constant for the exchange of a particular coordinated solvent molecule in the first coordination sphere (for example, solvent molecule number 2, if the solvent molecules are numbered from 1 to n, where n is the coordination number for the solvated metal ion, [MS ]m+). Thus, the equation for solvent exchange may be written ... 

Valuable information on mechanisms has been obtained from data on solvent exchange (4.4).The rate law, one of the most used mechanistic tools, is not useful in this instance, unfortunately, since the concentration of one of the reactants, the solvent, is invariant. Sometimes the exchange can be examined in a neutral solvent, although this is difficult to find. The reactants and products are however identical in (4.4), there is no free energy of reaction to overcome, and the activation parameters have been used exclusively, with great effect, to assign mechanism. This applies particularly to volumes of activation, since solvation differences are approximately zero and the observed volume of activation can be equated with the intrinsic one (Sec. 2.3.3). 

In these equations the hydrogen atoms written before and after the symbol S are not equivalent and the latter is not rapidly exchangeable with the solvent. Applying equation (56) to the composite scheme, one apparently obtains equation (151), which differs from equation (144) for the single-step mechanism. 

This has the same form with respect to [A] as Equation 8.7—thus, the rate expression is not necessarily definitive of mechanism, but the physical meanings of the constituent rate constants will be dilferent for A and D processes. The question then becomes whether these constituent rate constants can be identified from an independent type of experiment—in particular, when X is the solvent, whether k, derived from Equation 8.10 is equal to the rate constant kex measured for solvent exchange. 

Volumes of activation A V x for solvent exchange on metal ions are less susceptible to compensatory errors than are A//js and AS X, since in the integrated form of Equation 8.13 assuming constant AV X... 

In another interesting preliminary communication, Bennetto and Caldin discuss the effect of solvent on the rate of formation of the complex between Ni + and bipy. They point out that the majority of the evidence in favour of mechanism Ila has been obtained in aqueous solution, and report an extension of previous work in methanol-water mixtures which had suggested that structural features of the solvent are at least as important as the nature of the metal ion in determining kf. They compare the overall values kt with the values of solvent exchange Atwi [equation (2)], as measured by n.m.r. (Table 1), and it is apparent that. Tos varies by at... 

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