Complexes group trends, formation constants

The separation of metals into distinct classes was based on empirical thermodynamic data, namely, trends in the magnitude of equilibrium constants that describe the formation of metal-ion/ligand complexes. On the basis of these criteria, metal ions can be divided into three groups hard, soft, and borderline. The partition of a particular ion in each group is shown in Figure 7.1 (Nieboer and Richardson 1980 see also Morgan and Stumm 1991). 

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