Identification of the Formal +2 Oxidation State of Plutonium: Synthesis and Characterization of {PuII[C5H3(SiMe3)2]3}−

Over 70 years of chemical investigations have shown that plutonium exhibits some of the most complicated chemistry in the periodic table. Six Pu oxidation states have been unambiguously confirmed (0 and +3 to +7), and four different oxidation states can exist simultaneously in solution. We report a new formal oxidation state for plutonium, namely Pu 2+ in [K(2.2.2-cryptand)][Pu II Cp″ 3 ], Cp″ = C 5 H 3 (SiMe 3 ) 2 . The synthetic precursor Pu III Cp″ 3 is also reported, comprising the first structural characterization of a Pu–C bond. Absorption spectroscopy and DFT calculations indicate that the Pu 2+ ion has predominantly a 5f 6 electron configuration with some 6d mixing.