Visible and Near-Infrared Emission by Samarium(III)-Containing Ionic Liquid Mixtures

Highly luminescent anionic samarium(III) β-diketonate and dipicolinate complexes were dissolved in the imidazolium ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][Tf2N]. The solubility of the complexes in the ionic liquid was ensured by a careful choice of the countercation of the samarium(III) complex. The samarium(III) complexes that were considered are [C6mim][Sm(tta)4], where tta is 2-thenoyltrifluoroacetonate; [C6mim][Sm(nta)4], where nta is 2-naphthoyltrifluoroacetonate; [C6mim][Sm(hfa)4], where hfa is hexafluoroacetylacetonate; and [choline]3[Sm(dpa)3], where dpa is pyridine-2,6-dicarboxylate (dipicolinate) and [choline]+ is (2-hydroxyethyl)trimethyl ammonium. The crystal structures of the tetrakis samarium(III) β-diketonate complexes revealed a distorted square antiprismatic coordination for the samarium(III) ion in all three cases. Luminescence spectra were recorded for the samarium(III) complexes dissolved in the imidazolium ionic liquid as well as in a conventional solvent, that is, acetonitrile or water for the β-diketonate and dipicolinate complexes, respectively. These experiments demonstrate that [C6mim][Tf2N] is a suitable spectroscopic solvent for studying samarium(III) luminescence. High-luminescence quantum yields were observed for the samarium(III) β-diketonate complexes in solution.