Scandium complexes hydroxo

The actual situation that exists in solutions of rare earth salts in either aqueous or non-aqueous solution is complicated by concentration effects that can lead to both inner and outer sphere anion coordination as well as to the possibility of hydroxo-containing species particularly in the case of scandium. Inner sphere complexes containing halide ions, nitrate ions, sulfate ions (Choppin, 1971) and even the perchlorate ion (Fratiello et al., 1973 Silber, 1974) have been identified. Consequently, the interpretation of results obtained from measurements of conductance, density, partial molal volume, reaction kinetics, formation constants, and solution spectra can be extraordinarily complicated. 

The fact that the scandium(III) ion has the 3d electronic configuration severely limits the kinds of physical methods that can be brought to bear on determining the nature of the chemical environment in its complexes. The Sc nuclide has 100% natural abundance and a high sensitivity compared to protons and NMR studies using Sc may well prove to be a powerful tool (Melson et al., 1974). NMR spectra of aqueous solutions of scandium(III) chloride, perchlorate, nitrate, and sulfate have been obtained and it has been demonstrated that the chemical shifts for Sc at very low concentrations for the chloride, bromide, and perchlorate are independent of the anion and may be characteristic of the [Sc(OH)] ion. At higher concentrations the chemical shifts are both anion- and concentration-dependent and reflect the formation of bromo and chloro complexes and in the case of the perchlorate, polymeric hydroxo species. The chemical shifts for the nitrate and sulfate are different from the others and indicate that even at low concentrations there must be significant quantities of the respective complexes. 

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-... 

Komissarova, L.N., Prutkova, N.M., and Pushkina, G.Y. (1971) Study of scandium hydroxo-complexes in aqueous solution. Zh. Neorg, Khim., 16, 1798-1801. Kovalenko, P.N., Agipa, L.T., and Evstifeev, M.M. (1966) Oscillopolarographic determination of precipitation pH and solubility product of samarium and dysprosium hydroxides. Zh. Neorg. Khim., 11, 2689 -2693. 

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See also in sourсe #XX -- [ ]

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