L Journal of Alloys and Compounds 275–277 (1998) 242–245 Spectroscopic studies of lanthanide picrate complexes with N,N- dimethylacetamide. Structure of the La compound a a a, b b * C.V.P. de Melo , G. Vicentini , P.C. Isolani , J. Zukerman-Schpector , E.E. Castellano a ˜ ˜ ´ Instituto de Quımica, Universidade de Sao Paulo, C.P . 26077, Sao Paulo, SP , 05599-970, Brazil b ˜ ˜ ´ Instituto de Fısica de Sao Carlos - USP C.P . 369, Sao Carlos, SP , 13560-970, Brazil Abstract Emission and excitation spectra were recorded for the complexes Ln(pic) .3(DMA) (pic5picrate, DMA5N,N-dimethylacetamide, 3 Ln5La, Eu, Gd, Sm, Lu). The Eu and Sm complexes exhibit f–f characteristic luminescence spectra, while the other present broad emission bands are due to picrate anion luminescence. Both emission and excitation spectra of the Eu compound point to a small 5 participation of the D state in the emission process. Lifetimes for these luminescences were measured. Their values (in the range of ms) 1 5 4 suggest a strong mixing of the singlet and triplet states of the ligands, as well as a fast transfer to the D and G states of Eu and Sm, 0 5/2 respectively. For the Sm complex doped with Eu, small variations in the lifetimes were observed. Luminescence quantum yields were also determined. Single-crystal X-ray analysis of the La complex shows a D symmetry around the central ion.  1998 Elsevier Science 3h S.A. Keywords: Lanthanum; N,N-dimethylacetamide; Picrate Addition compounds between lanthanide salts and N,N- Hitachi MPF-4 spectrofluorimeter with modifications [11]. dimethylacetamide (DMA) have been studied [1–8]. Lan- Emission lifetimes were measured on an Edinburgh FL thanide picrate complexes with DMA, with compositions 900 spectrofluorimeter equipped with a pulsed hydrogen Ln(pic) .3(DMA) were synthesized. According to the X- lamp (40 kHz, 1 ns FWHM). This very short excitation 3 ray powder patterns, three types of diffractograms were time precluded the use of deconvolution procedures for obtained: La–Pr; Nd–Yb, Y; and Lu. The structure of the calculating the emission lifetimes. Emission quantum Sm compound, belonging to the second isomorphous yields were determined using the method developed by series, was determined [9]. The emission spectrum of the Wrighton [12] on a Hitachi MPF-4 spectrofluorimeter. Eu compound was observed as a function of temperature, Single-crystal X-ray diffraction analysis of the La 31 evidencing a D symmetry around the Eu ion and compound was carried out on an Enraf-Nonius CAD-4 3h showing a phase transition at 172 K [10]. In this paper, a diffractometer, using graphite-monochromated Mo Ka spectroscopic study of the Eu and Sm compounds, which radiation. Most of the calculations were performed on a present lanthanide f–f luminescence, as well as some other VAX computer with SHELX 76 [13], SHELXS 86 [14] representative compounds (La, Gd, Lu), which show and ORTEP [15] programs. picrate luminescence, are reported. In an attempt to study The synthesis and characterization of the compounds the first isostructural series of these compounds, X-ray have already been described in a previous paper [9]. Doped analysis of La(pic) .3(DMA) was carried out and its samarium compounds were synthesized with 1 and 2 wt. % 3 structure is described. hydrated europium picrate added to the Sm salt prior to the complex synthesis. 1. Experimental 2. Results and discussion Emission and excitation spectra were recorded on a In a previous paper [10] the characteristic f–f emission * spectrum of the complex Eu(pic) .3(DMA) was presented, Corresponding author. Tel.: 155 11 818 3876; fax: 155 11 818 3876; 3 31 e-mail: pcisolan@quim.iq.usp.br pointing out to a D symmetry around the Eu ion. Fig. 3h 0925-8388 / 98 / $19.00  1998 Elsevier Science S.A. All rights reserved. PII: S0925-8388(98)00312-0