Lanthanide
Ln(II) and Ln(IV) compounds

The most common divalent derivatives of the lanthanides are for Eu(II), which achieves a favorable f configuration. Divalent halide derivatives are known for all of the lanthanides. They are either conventional salts or are Ln(III) " electride "-like salts. The simple salts include YbI, EuI, and SmI. The electride-like salts, described as Ln, 2I, e, include LaI, CeI and GdI. Many of the iodides form soluble complexes with ethers, e.g. TmI (dimethoxyethane). Samarium(II) iodide is a useful reducing agent. Ln(II) complexes can be synthesized by transmetalation reactions. The normal range of oxidation states can be expanded via the use of sterically bulky cyclopentadienyl ligands, in this way many lanthanides can be isolated as Ln(II) compounds.

Ce(IV) in ceric ammonium nitrate is a useful oxidizing agent. The Ce(IV) is the exception owing to the tendency to form an unfilled f shell. Otherwise tetravalent lanthanides are rare. However, recently Tb(IV) and Pr(IV) complexes have been shown to exist.
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