Formation and Solvent Structure

The kinetics of the reactions of cobalt(ii), nickel(ii), copper(ii), and zinc(ii) with pyridine-2-azo-p-dimethylaniline [pada (7)] in glycerol solution provide a 

Striking example of the role of the solvent in determining rates of complex formation. The most important feature of the results is the observation that rates of formation vary very little with the nature of the metal cation in glycerol solution, whereas previous studies have shown that rates of formation of pada complexes vary greatly with the cation in aqueous media. It seems that whereas 

Water is, of course, a solvent with marked and frequently discussed structural features. The majority of recent work on complex formation kinetics in which water is involved has been concerned with mixed solvents, containing smaller or greater amounts of organic components added to modify the structure of the water, and is therefore referenced in the following section. One reaction in aqueous solution in which solvent structure is thought to be an important factor is that of the exchange of glycine with the [VOH(gly)] + cation. Here there are some deviations from normal kinetic behaviour, which may be ascribed to solvent structural effects. 

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