Dioxo ions, actinide elements

The known oxidation states of the actinides are given in Table 20-3. With the exception of Th and Pa, the common oxidation state, and for trans-americium elements the dominant oxidation state, is +3, and the behavior is similar to the +3 lanthanides. Thorium and the other elements in the +4 state show resemblances to HfIv or Ceiv, whereas Pa and the elements in the +5 state show some resemblances to Tav. Exceptions to the latter statement are the dioxo ions MOJ for U, Np, Pu, and Am that are related to the M02+ ions in the +6 state. Redox potentials are given in Table 20-4. 

The majority of the chemistry that has been investigated for the actinide elements has been in aqueous solutions. For the light actinides in acidic solutions, four types of cations persist trivalent, tetravalent, pentavalent, and hexavalent. The later two ions are always found to have trans oxo ligands, making up a linear dioxo unit. Actinide ions of this type are typically referred to yls and have the names, uranyl (1, U02+/ +), neptunyl (2, Np02+ +), plutonyl (3, Pu02+ +), (4, Am02+/ ) and so on. 

It is frequently argued that a specific property of 5f g oup M(VI) nd M(V) is the formation of linear dioxo complexes, M022 and M02. Their most striking property is the coexistence of oxo and aquo ligands, which is exceedingly rare in the rest of the elements. There are characteristic differences found frequently between the oxo ions of the V- and VI-valent actinides, uranium through americium, and those of the d elements in the same valence states. 

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