Formation of Polynuclear Complexes Polymerization

The hydrolysis of metallie ions often leads to hydroxo polynuclear complexes. In water, for example, Fe(ni) gives rise to the following equilibria (simplified writing)  

Notice the symbolism of equilibrium constants Xy and Py, where i is the number of metallic ions and j that of bound ligands. The structure of the di-p-hydroxooctaaquadiiron(III) complex involves the occurrence of bridges through hydroxyl groups linking the two ferric ions  

It may also be considered as resulting from the dimerization of the di(hydroxo)-iron(II) complex [Fe(OH)2]+ according to the reaction 

Several metallic ions give bridged ions beryllium(II), tin(II), bismuth(III), and copper(II), for example. 

These phenomena find expression in the presence of supplementary equilibria that actually govern them and that interfere with those corresponding to the complex under interest. Constants Kjj (or p ), together with those already handled with mononuclear complexes, permit us to calculate the concentrations of the different species, including those of the polynuclear hydroxo complexes. 

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