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(OtBu)3)4], 1-Tb, with the tris­(4-bromophenyl)­amminium oxidant, [N­(C6H4Br)3]­[SbCl6], to afford the Tb4+ complex [Tb­(OSi­(OtBu)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.