Structures and Properties of Luminescent Pentanitratoeuropate(III) Ionic Liquids

A series of luminescent ionic liquids based on pentanitratoeuropate(III) anions combined with imidazolium cations, namely, 1,2,3-trimethylimidazolium {[MC(1)mim](2)[Eu(NO3)(5)] (1)}, 1,3-dimethylimidazolium {[C(1)mim](2)[Eu(NO3)(5)] (2)), 1-elhyl-3-methylimidazolium [[C(2)mim](2)[Eu(No-3)(5)] (3)}, 1-butyl-3-methylimdazolium {[C(4)mim](2)[Eu(NO3)(5)] (4)}, 1-hexyl-3-methylimidazolium {[C(6)mim](2)[Eu(NO3)(5)] (5)}, and 1-methyl-3-octylimidazolium {[C(8)mim](2)[Eu(NO3)(5)] (6)}, were synthesized. These complexes were characterized by NMR and IR spectroscopy as well as elemental analysis. They exhibit high thermostability and wide liquidus ranges of more than 300 degrees C. Colorless plate crystals of 1 were isolated, and the crystal structure was determined by single-crystal X-ray diffraction [monoclinic system, C2/c space group with the cell parameters a = 21.6870(6) angstrom, b = 9.9807(4) angstrom, c = 15.0267(6) angstrom, beta = 131.140(4)degrees, Z = 4]. In the [Eu(NO3)(5)](2-) anion, the 10-coordinate Eu-III ion is coordinated by five bidentate Filtrate ligands and has a highly symmetrical trigonal-bipyramidal geometry. Compounds 1-6 exhibit bright red luminescence of high colorimetric purity. Only two characteristic narrow monochromatic bands, arising from the D-5(0)-> F-7(J) (J = 1 and 2) intraconfigurational f-f transitions, were clearly observed in their emission spectra at 298 K. The intense red photoluminescence, is still stable at 150 degrees C. These 10-coordinated Eu-III complexes are of interest as potential thermally stable luminescent soft materials.