The recent isolation of [K(crypt)][Cp″3MII] (M = La, Ce, Pr, Th, U, Np, and Pu; Cp″ = C5H3(SiMe3)2; crypt = 2.2.2-cryptand) and [K(crypt)][Cp′3MII] (M = La, Ce, Pr, Gd, Tb, Ho, Er, Lu, and U; Cp′ = C5H4SiMe3) has shown for the first time that the +2 oxidation state of these metals can exist in crystallographically-characterizable complexes. In these initial studies, the [K(crypt)]1+ cation appeared to be crucial to isolating these species. This presentation will describe how a much more diverse set of countercations has led to isolation of new examples of these metals in low oxidation states. Specifically, the isolation of [(C5H4Me)3LnII]1− (Ln = Tb, Ho, and Er) with an inverse sandwich countercation, [(18-crown-6)K(µ-C5H4Me)K(18-crown-6)]1+, will be described as well as isolation of new U(II) complexes in the absence of a chelating agent, namely the [Li(THF)4][Cp″3U] salt and the oligomeric [Cp″UII(μ-Cp″)2Cs(THF)2]n complex. An unusual Th(III) square planar complex has also been identified in the absence of a chelating agent with the mixed solvated cation [K(THF)5(Et2O)]1+.

Importance of countercations in isolating new crystalline examples of complexes of f-elements in low oxidation states

2019 Spring National Meeting

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