Complexation strength

The complex strength increases with the effective charge of the acceptor ion, i.e. in the order Pult+>Pu022+ Pu +>Pu02+. 

For low selenosulphate concentrations, only the small crystals were formed, even in thicker films, and this was rationalized by the lower steady-state selenide concentration, which would favor cluster growth over ion-by-ion formation (the product of free lead and selenide ions needs to be larger than the solubility product of PbSe for ion-by-ion deposition to occur). An important difference between the citrate depositions and the NTA or hydroxide ones is that, even in the ion-by-ion citrate deposition, some low concentration of colloidal hydrated oxide was present, due to the relatively low complexing strength of citrate. The pH of the hydroxide baths (> 13) was much higher than that of the citrate or NT A baths (10.8). 

For any particular type of Lewis base, say an amine or carboxylate group, metals of smaller radius generally form the stronger complex. This produces the well-known Irving-Williams series of complexing strength for the divalent metal ions ... 

For cations formed from metals in early groups in the periodic table the complexing strength with halide ions follows the sequence... 

Definition of hard/soft character is the result of empirical observations and trends in measured stability of complexes. For example, hard acids (such as Fe3+) tend to bind the halides in the order of complex strength of F > Cr > Br > I, and soft acids (such as Hg2+) in the reverse order of stability. However, as with any model with just two categories, there will be a grey area in the middle where borderline character is exhibited. This is the case for both Lewis acids and Lewis bases. Selected examples are collected in Table 3.2 below a more complete table appears later in Chapter 5. 

The extraction behavior of No + in a tri-n-octylamine-HCl system was compared with that of divalent Hg, Cd, Cu, Co, and Ba (27). This experiment provided a test of the chloride complex strength of No2+ because the amine anion-exchanger will only extract anionic species. It was found that Ba + and No + were not extractable over a range of 0.2 to 10 M HC1, while the other divalent ions of Hg, Cd, Cu, and Co were strongly extracted. 

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