title: Synthesis, crystal structure and luminescence properties of the Ln(III)-picrate complexes with 1-ethyl-3-methylimidazolium as countercations.
abstract: 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.
authors.affiliation: Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Belo Horizonte, MG 31270-901, Brazil; Departamento de Química e Biologia, Instituto Federal de Educação, Ciência e Tecnologia do Espírito Santo, Vitória, ES 29040-780, Brazil.
authors.forename: Alex S
authors.initials: AS
authors.lastname: Borges
authors.forename: Jeferson G
authors.initials: JG
authors.lastname: Da Silva
authors.forename: José D
authors.initials: JD
authors.lastname: Ayala
authors.forename: José Diogo L
authors.initials: JD
authors.lastname: Dutra
authors.forename: Nivaldo L
authors.initials: NL
authors.lastname: Speziali
authors.forename: Hermi F
authors.initials: HF
authors.lastname: Brito
authors.forename: Maria Helena
authors.initials: MH
authors.lastname: Araujo
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D004735:Energy Transfer; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids; D028581:Lanthanoid Series Elements / Q000737:chemistry* / Q000378:metabolism; D049449:Luminescence; D008956:Models, Chemical; D008962:Models, Theoretical; D010851:Picrates / Q000737:chemistry* / Q000378:metabolism
chemical_list: D007093:Imidazoles; D052578:Ionic Liquids; D028581:Lanthanoid Series Elements; D010851:Picrates; C005858:picric acid; C518739:1-ethyl-3-methylimidazolium
keywords: Crystalline structure; Lanthanide picrate; Photoluminescence properties; Sparkle model