Terbium complex with +4 oxidation state synthesized

Down toward the bottom of the periodic table lie the lanthanides. These f-block elements form complexes in which the metals usually exist in the +3 or, more recently, +2 oxidation states. The only lanthanide known to form molecular Ln⁴⁺ compounds was cerium. But researchers at the Swiss Federal Institute of Technology, Lausanne (EPFL), led by Marinella Mazzanti, now show that terbium can also form compounds with a +4 oxidation state (J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.9b05337). Perhaps, they say, other lanthanides can too. To make the Tb⁴⁺ complex, the team first synthesized a complex containing electron-rich tetrakis(tert-butoxy) siloxide ligands and two metal centers, potassium and terbium(III). They then oxidized it with a strong oxidizing agent to give [Tb(OSi(O^t-Bu)₃)₄]. The team confirmed the oxidation state of terbium with electron paramagnetic resonance and magnetometry and also measured the Tb³⁺/Tb⁴⁺ redox potential. Ce⁴⁺ compounds have a high oxidizing power that has led to applications in catalysis and material science. Perhaps, Mazzanti hopes, these applications could be expanded with other Ln⁴⁺ ions.