Synthesis, crystal structure and luminescence properties of the Ln(III)-picrate complexes with 1-ethyl-3-methylimidazolium as countercations.

New anionic complexes of lanthanide picrates containing 1-ethyl-3-methylimidazolium (EMIm) as countercation have been prepared. The Ln(III) complexes were characterized by complexometric titration, elemental analyses, infrared spectroscopy and molar conductivity. The molecular structures of the (EMIm)2[Ln(Pic)4(H2O)2]Pic complexes, Ln(III)=Sm, Eu, Gd and Tb, and Pic=picrate, were determined by X-ray crystallography. In these structures the picrate anion appears in three forms: as uncoordinated counteranion, as monodentated and bidentate ligand. The coordination polyhedron around the Ln(III) atom can be described as tricapped trigonal prismatic molecular geometry. The theoretical molecular structures of the complexes were also calculated using the Sparkle/PM3 model for Ln(III) complexes, allowing analysis of intramolecular energy transfer processes of the Eu(III) compound. The spectroscopic properties of the 4f(6) intraconfigurational transitions of the Eu(III) complex were then studied experimentally and theoretically. The low value of emission quantum efficiency of (5)D0 emitting level (η) of Eu(III) ion (ca. 10%) is due to the vibrational modes of the water molecule that act as luminescence quenching. In addition, the luminescence decay curves, the experimental intensity parameters (Ωλ), lifetimes (τ), radiative (Arad) and non-radiative (Anrad) decay rates, theoretical quantum yield (q) were also determined and discussed.

Natural perovskite: (Ca(0.95†(1))Ce(0.011†(2))Na(0.010†(4)))(Fe(0.022†(2))Ti(0.98†(1)))O(3).

A natural sample of perovskite (calcium caesium sodium iron titanium oxide) from the Tapira Alkaline Complex in southeastern Brazil was found by electron microprobe analysis to have the chemical formula (Ca(2+) (0.95 (1))Ce(3+) (0.011 (2))Na(+) (0.010 (4)))(Fe(3+) (0.022 (2))Ti(4+) (0.98 (1)))O(2-) (3) and by IR spectroscopy to be an anhydrous mineral. Oxygen anions are arranged around Ti(4+) in an almost perfect octa-hedron and around Ca(2+) in a distorted 12-fold polyhedron.