Scandium complexes hydrated ions

It might be expected that, since the Sc + ion has a considerably greater crystal radius than the corresponding tripositive ions of the 3d metals (compare Sc + at 0.885 A with Ti +, Cr +, and Fe + at 0.810, 0.755, and 0.785 A, respectively), coordination numbers greater than six might be conunon in scandium complexes. With the exception of the aqua ion (and nitrate complexes), this has not been realized, but studies of scandium chemistry are still relatively rare (partly on account of cost). Aqua complexes and simple hydrates have been discussed in Solvento Complexes of the Lanthanide Ions. 

Scandium, Sc, which was first isolated in 1937, is a reactive metal it reacts with water about as vigorously as calcium does. It has few uses and is not thought to be essential to life. The small, highly charged Sc3+ ion is strongly hydrated in water (like Al3+), and the resulting Sc(H2())6]3+ complex is about as strong a Bronsted acid as acetic acid. 

The j8-diketones are excellent chelating ligands for the rare earth ions and typical examples of the types of complexes that are formed are presented in table 25.14. (The functioning of these complexes as lasers is discussed in ch. 35.) The complexes that might have been expected, R(jS-diketone)3, rarely form, except for scandium, because of the tendencies of these compounds to add one or more additional ligands, particularly water molecules. Attempts to dehydrate most of these hydrated species leads either to destruction of the complex or the formation of polymeric hydroxo species (Pope et al., 1961). If, however, the substituents on the j8-diketone are large, t-butyl groups as an example, then the anhydrous tris chelate can be prepared (eisentraut and Sievers, 1965). The anhydrous trisacetylacetonato complexes have been prepared, however, in the absence of any possible adduct formation by the reaction of acetylacetone directly with a rare earth hydride (Przystal et al., 1971). The anhydrous acetyl-... 

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