Scandium polymeric hydrolysis species

Table 8.1 Selected stability constants at zero ionic strength and 25 °C for scandium polymeric hydrolysis species and the assodated ion interaction coefficients for perchlorate media.

The data selected for the stability constants of the polymeric hydrolysis species of scandium at zero ionic strength are listed in Table 8.1. Also listed in the table are the ion interaction coefficients (both sets of interaction coefficients have been acquired using the standard specific ion interaction theory where it is assumed that As2 = 0). The data used to determine these values are illustrated in Figures 8.2 and 8.3 for the Sc2(OH)2 and Sc3(OH)5 species, respectively. 

There have been a few studies that have provided evidence for the formation of polymeric hydrolysis species of scandium(III). There has been good agreement between the studies both in terms of the polymeric species that form and the magnitude of the stability of each species. As indicated earlier, the majority of studies have been interpreted with the two polymeric species, Sc2(OH)2 and Sc3(OH)5 +, in addition to the monomeric ScOH + species. The formation of a third polymeric species, Sc3(OH)4 , is not considered reliable in the present review and stability constant data for this latter species are not retained. The data available in the literature are listed in Table 8.5. 

Table 8.5 Data for the stability constants of polymeric scandium(lll) hydrolysis species (reaction (2.5), M = Sc3+,p>l). 

The smaller ionic radius also leads to extensive hydrolysis, which helps to explain why scandium compounds are more difficult to crystallize than those of the lanthanides and why the number of basic compounds is large. In aqueous solutions, depending on the pH, the Sc ion can be presented as [Sc(H20)g] +, [Sc(H20)50H] + and [Sc(H20)5(0H)]2 (Komissarova, 1980) there is also evidence for the formation of other polymeric species (Biedermann et al., 1956). The main product of polynuclear hydrolysis for Sc +, + as well as for In appears to... 

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