Exchange rates of aquo ions

Lanthanides are class II metals [66] characterized by fast solvent exchange rates of aquo ion... 

The Inner-Shell Reorganization Energy Exchange Rates of Aquo Ions... 

In other words, the complex formation rate constant kf [M1 s 1] depends on the outer sphere electrostatic encounter and on the water exchange rate of the aquo metal ion k w... 

In addition to the data on the aquation reactions (Table I), it is also known (5) that isomerization of the chloro-aquo products can take place. Equation 12 is sufficient to permit isomerization by an intermolecular process, but it is an over-simplification of what happens in the experiments described above. Equilibria for the replacement of the second chloro group, as well as acid-base equilibria between aquo and hydroxo species, must also be involved. Less complicated is the isomerization of m-[Co(en)2Cl2] in methauol solution where the rate of rearrangement equals the rate of chloride ion exchange (48),... 

Dale Margerum Ralph Wilkins has mentioned the interesting effect of terpyridine on the subsequent substitution reaction of the nickel complex. I would like to discuss this point—namely the effect of coordination of other ligands on the rate of substitution of the remaining coordinated water. However, before proceeding we should first focus attention on the main point of this paper-which is that a tremendous amount of kinetic data for the rate of formation of all kinds of metal complexes can be correlated with the rate of water substitution of the simple aquo metal ion. This also means that dissociation rate constants of metal complexes can be predicted from the stability constants of the complexes and the rate constant of water exchange. The data from the paper are so convincing that we can proceed to other points of discussion. 

In the case of Gd3+, there is a rapid water exchange with respect to the relaxation 7im [28]. For water exchange reaction of Gd3+ aquo ion the water tumbling time is 7 x 10 11 s. When Gd3+ is bound to a macromolecule, part of the hydration sphere is substituted by a protein molecule, the effective correlation changes (i.e.) effectively it becomes the electron relaxation time [29] which is about 10-9 s. By virtue of binding to a macromolecule, a net enhancement in proton relaxation rate, Eq is observed which is characteristic of the Gd3+ complex and depends on the resonance frequency and temperature. Some data on the enhancements obtained for Gd3+ protein complexes are given in Table 11.5. 

The rate of exchange between aquo-ferrous ions and the tris bipyridyl and phenanthroline complexes of Fe(II) shows a first-order dependence on [H+] (731), but with the exception of 4,7-(OH)2-phenanthroline the rate parameters for dissociation in dilute sulfuric acid vary little with ligand substituent for the Fe(II) complexes (114). For the tris-bipyridyl complexes at low acidities, the overall rate constants show both an acid-dependent and an independent term (116). In view of the dissociation rate constants for the monophenanthroline-Ni(II) complexes (232) this lack of discrimination between the complexes of the various sub-, stituted ligands is surprising, presumably being a function of the spin change associated with dissociation. The overall rate constant for the dissociation of the ferrous complexes in basic solution shows a more... 

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