Formation from other polynuclear species

There are few data for the first monomeric hydrolysis constant of copper(II). The reviews of Plyasunova et al. (1997) and Powell et al. (2007) both favoured the data of Paulson and Kester (1980) however, these data are not consistent with other low ionic strength data (Arena et al., 1976 Sylva and Davidson, 1979) that were also able to detect the formation of the dominant polynuclear species of cop-per(II). Data are also available for this stability constant at elevated temperatures from Var yash (1985). This latter data are used from 100 to 350 "C, whereas other available data are preferred at lower temperatures. When these data are assessed, it is clear that the stabihty constant derived for 25 °C and zero ionic strength is more positive than that which would be derived from the fixed ionic strength data of Paulson and Kester (1980). Due to these facts, the data of Paulson and Kester (1980) are not retained in this review. Data for the stability constant of CuOH" are listed in Table 11.54. 

As with uranium, the solution chemistry is complicated, owing to hydrolysis and polynuclear ion formation, complex formation with anions other than perchlorate, and disproportionation reactions of some oxidation states. The tendency of ions to displace a proton from water increases with increasing charge and decreasing ion radius, so that the tendency to hydrolysis increases in the same order for each oxidation state, th at is, Am > Pu > Np > U and M4+ > M02+ > M3+ > M02 simple ions such as Np02OH+ or PuOH3+ are known in addition to polymeric species that in the case of plutonium can have molecular weights up to 1010. 

Other anions with which Fe(III) forms complexes are the silicates Fe(II) is less reactive with these species. This is used to limit the separation of hydrated Fe2 03 from waters, e.g. in water mains (this also concerns hydrated Mn(III) and Mn(IV) oxides). In waters containing 15-20 mg 1 Si the Fe2 03 separates with difficulty. It is best stabilized in alkaline media at pH 7.5. The formation of cationic or anionic complexes is supposed, e.g. [FeSiO(OH)3] and [Fe(OH).O.Si(OH)3]. At higher concentrations of iron, polynuclear complexes can be formed. 

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