Europium-containing ionic liquids and crystal complexes based on phosphine oxides

We synthesized two Eu-containing ionic liquids (ILs) [Eu(TOPO)4(NO3)2]NTf2 and [Eu(TBPO)4(NO3)2]NTf2, and a crystal [Eu(TPhPO)4(NO3)2]NTf2. In these complexes, TOPO (Tri-n-octylphosphine oxide) and TBPO (Tri-n-butylphosphine oxide) coordinate with Eu3+ constituting the cations, while NTf2− (bis(trifluoromethylsulfonyl)imide anion) acts as the counter anion. The crystal structure of [Eu(TPhPO)4(NO3)2]NTf2 showed the details of the coordinated condition. The infrared spectra of all the complexes exhibited some typical features of the phosphine oxides and two bidentate nitrates. [Eu(TRPO)4(NO3)2]+ (R = octyl and butyl) were proved to exist in the C2H2Cl2 solutions by 31P NMR of [Eu(TOPO)4(NO3)2]NTf2 and [Eu(TBPO)4(NO3)2]NTf2. The luminescence emissions also gave information about the same coordination environments. Thermogravimetric analyses (TGA) indicated that the NTf2− group determined the decomposition temperatures of the three complexes. These complexes are the first tetra-phosphine oxide complexes constituted by Eu(NO3)3 and phosphine oxides in the presence of NTf2−. The structural difference between [Eu(TRPO)4(NO3)2]NTf2 in this work and Eu(TRPO)3(NO3)3 formed in traditional organic solvent can help understand that new extraction species may exist in the NTf2−-based IL extraction system different from those in the normal organic solvent extraction system.

Graphical abstractWe synthesized two Eu-containing ionic liquids [Eu(TOPO)4(NO3)2]NTf2 and [Eu(TBPO)4(NO3)2]NTf2, and a crystal [Eu(TPhPO)4(NO3)2]NTf2. In these compounds, TOPO and TBPO coordinate with Eu3+ and constitute the cations, while NTf2− acts as the anion counterpart.Figure optionsDownload full-size imageDownload as PowerPoint slide