Synthesis, crystal structure and luminescence properties of the Ln(III)-picrate complexes with 1-ethyl-3-methylimidazolium as countercations Alex S. Borges a,e , Jeferson G. Da Silva a , José D. Ayala a , José Diogo L. Dutra b , Nivaldo L. Speziali c , Hermi F. Brito d , Maria Helena Araujo a,⇑ a Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Belo Horizonte, MG 31270-901, Brazil b Departamento de Química, Centro de Ciências Exatas e Tecnologia, Universidade Federal de Sergipe, São Cristóvão, SE 49100-000, Brazil c Departamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Belo Horizonte, MG 31270-901, Brazil d Instituto de Química, Universidade de São Paulo, C.P. 26077, CEP 05513-970, São Paulo, SP, Brazil e Departamento de Química e Biologia, Instituto Federal de Educação, Ciência e Tecnologia do Espírito Santo, Vitória, ES 29040-780, Brazil highlights  Photoluminescence spectroscopy of new Ln-picrate complexes with Ionic liquid.  Picrate appears as uncoordinated counteranion and as mono and bidentate ligand.  For Eu(III) and Sm(III) complexes the picrate ligand acts as luminescent sensitizer. graphical abstract article info Article history: Received 7 November 2012 Received in revised form 29 June 2013 Accepted 10 August 2013 Available online 3 September 2013 Keywords: Lanthanide picrate Crystalline structure Photoluminescence properties Sparkle model abstract New anionic complexes of lanthanide picrates containing 1-ethyl-3-methylimidazolium (EMIm) as coun- tercation have been prepared. The Ln(III) complexes were characterized by complexometric titration, ele- mental analyses, infrared spectroscopy and molar conductivity. The molecular structures of the (EMIm) 2 [Ln(Pic) 4 (H 2 O) 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 experimen- tally and theoretically. The low value of emission quantum efficiency of 5 D 0 emitting level (g) 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 (X k ), lifetimes (s), radiative (A rad ) and non-radiative (A nrad ) decay rates, theoretical quantum yield (q) were also determined and discussed. Ó 2013 Elsevier B.V. All rights reserved. 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.08.039 ⇑ Corresponding author. Tel.: +55 31 34097557; fax: +55 31 34095700. E-mail address: maria.araujo@pq.cnpq.br (M.H. Araujo). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 718–727 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa