Ionic Liquids [M(3+)][A(−)](3) with Three‐Valent Cations and Their Possible Use to Easily Separate Rare Earth Metals

We introduce a simple way to liquify rare earth metals (REM) by incorporating the corresponding cations, in particular Eu(3+), La(3+), and Y(3+), into polyvalent ionic liquids (ILs). In contrast to conventional methods, this is achieved not by transforming them into anionic complexes, but by keeping them as bare cations and combining them with convenient, cheap and commercially available anions (A) in the form [REM(3+)][A( − )](3). To do so, we follow the COncept of Melting Point Lowering due to EThoxylation (COMPLET) with alkyl polyethylene oxide carboxylates as anions. We provide basic properties, such as glass transition temperatures, viscosities, electrical conductivities, as well as water‐octanol partition constants P and show that these ILs have remarkably different properties, despite the similarity of their cations. In addition, we show that the ionic liquids possess interesting luminescent properties as non‐conventional fluorophores.