Solvent exchange volumes of activation for

DR. SWADDLE We are measuring the volume of activation for solvent exchange in a region where it is in the NMR time frame in other words, where the NMR line broadening is exchange controlled, i.e., k = 1(T s. ... 

Volumes of activation for solvent exchange on Be2 + ions were obtained experimentally some time ago.176 The values ranged from distinctly negative (—13.6 cm3/ mol for water), indicative of a limiting A mechanism, to distinctly positive ( + 10.5 cm3/mol for tmu (tmu = /V,/V,/V,/V-tetramethylurea)), indicative of a limiting... 

Volumes of activation for solvent exchange on high spin, first row divalent and trivalent transition metal ions are available in water and in a variety of non-aqueous solvents. The AF values indicate that the mechanism for solvent exchange is not unique, but progressively changes from an associative activation mode for the early elements to a dissociative activation mode for the later ones. 

The reactions just mentioned all proceed via an outer-sphere electron transfer mechanism. By way of comparison, the volume of activation for the exchange reaction in Fe(H20)50H /Fe(H20)6 was reported to be + 0.8 cm mol", that is, significantly more positive than that found for Fe(H20)e (9). This difference was ascribed to the release of a solvent molecule associated with the formation of a hydroxo-bridged intermediate in terms of an inner-sphere mechanism. 

A variety of geometries have been established with Co(II). The interconversion of tetrahedral and octahedral species has been studied in nonaqueous solution (Sec. 7.2.4). The low spin, high spin equilibrium observed in a small number of cobalt(Il) complexes is rapidly attained (relaxation times < ns) (Sec. 7.3). The six-coordinated solvated cobalt(ll) species has been established in a number of solvents and kinetic parameters for solvent(S) exchange with Co(S)6 indicate an mechanism (Tables 4.1-4.4). The volumes of activation for Co " complexing with a variety of neutral ligands in aqueous solution are in the range h-4 to + 1 cm mol, reemphasizing an mechanism. 

Volume of activation. The following values were obtained for the rate of exchange of r/ms-Co(en)2(H280)2+ and solvent at 308 K.28 Calculate AT. What is the implication of that value for the mechanism ... 

Solvent exchange processes are the most fundamental substitution reactions that characterize the lability and reaction mechanism of a metal center within a coordination geometry. For these reactions the interpretation of the volume of activation becomes rather straightforward since these reactions do not involve major changes in solvation due to changes in dipole moments and electrostriction, which can in... 

An attempt is made to account quantitatively for the volumes of activation, AV, of ligand substitution processes. Causes of the pressure-dependence of AV include solvational change, for which a versatile analysis is developed. The pressure-independent AV values of solvent exchange reactions are good measures of the non-sol-vational components of AV for related net reactions. For water exchange, one can predict... 

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