Molecular Complex of Tb in the +4 Oxidation State

Lanthanides (Ln) usually occur in the +3, or more recently the +2, oxidation states. The only example of an isolated molecular Ln⁴⁺ so far remains Ce⁴⁺. Here we show that the +4 oxidation state is also accessible in a molecular compound of terbium as demonstrated by oxidation of the tetrakis(siloxide)terbium(III) ate complex, [KTb(OSi(O ^tBu)₃)₄], 1-Tb, with the tris(4-bromophenyl)amminium oxidant, [N(C₆H₄Br)₃][SbCl₆], to afford the Tb⁴⁺ complex [Tb(OSi(O ^tBu)₃)₄], 2-Tb. The solid state structures of 1-Tb and 2-Tb were determined by X-ray crystallography, and the presence of Tb⁴⁺ was unambiguously confirmed by electron paramagnetic resonance and magnetometry. Complex 2-Tb displays a similar voltammogram to the Ce⁴⁺ analogue but with redox events that are about 1 V more positive.