Materials Chemistry and Physics 114 (2009) 134–138 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys The structure and spectroscopy of lanthanide(III) complexes with picolinic acid N-oxide in solution and in the solid state Stefan Lis ∗ , Zbigniew Piskuła, Maciej Kubicki Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Pozna´ n, Poland article info Article history: Received 17 May 2008 Accepted 26 August 2008 Keywords: Europium(III) Complexes Picolinic acid N-oxide Luminescence Crystal structure abstract The spectroscopic characteristics and the crystal structure of Eu(III) complex with picolinic acid N-oxide ligand, picNO, at room and liquid-nitrogen temperatures are discussed. Studies concerning the Eu(III) ion luminescence (intensity, luminescence lifetime measurements, and excitation spectra of the 5 D 0 → 7 F 0 transition) are presented. The selective excitation luminescence spectroscopy of Eu(III) in the range of the 5 D 0 → 7 F 0 transition is used for the study of Eu/picNO complexes in solution equilibria. In the crys- tal the complex molecules build the two-dimensional structures with additional Na + cations and water molecules. This structure consists of edge-sharing chains of Na distorted octahedral, interconnected by Eu polyhedra (distorted square antiprisms). The ligand, pyridine-2-carboxylate-1-oxide, coordinates to the Eu(III) ion as an ionic bidentate chelate, forming the Na[Eu(picNO) 4 ] complex of six-membered chelate rings with the bite angles of ca. 70.5 ◦ . The complex is symmetrical; the Eu(III) ion is eight-coordinated. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Lanthanide complexes of pyridine carboxylic acid N-oxides and their substituted derivatives have been subjects of several pub- lications [1–7] due to their interesting photophysical properties. Complexes of Ln(III) ions with isomers of pyridine carboxylic acid, namely picolinic acid N-oxide, nicotinic acid N-oxide, and isonico- tinic acid N-oxide, have been investigated because of their possible applications [4,7]. The pyridine N-oxide group often acts as O donor coordination mode [5]. So it is self-evident that systems bearing N-oxide groups form more stable complexes with lanthanides than the parent ligands [5,6]. Pyridine carboxylic acid N-oxides and their substituted derivatives, having oxygen donor atoms, form ther- modynamically stable six-membered ring complexes. Only Ln(III) complexes with nicotinic acid N-oxide, isonicotinic acid N-oxide, and 6-methyl-picolinic acid N-oxide have been structurally deter- mined [7,8]. In this paper, we describe the crystal structure and the spectroscopic characteristics of Eu(III) complexes with picNO lig- and at room and liquid-nitrogen temperatures. Studies concerning the Eu(III) ion luminescence (intensity, luminescence lifetime mea- surements, and excitation spectra of the 5 D 0 → 7 F 0 transition) are presented. We used luminescence spectroscopy of the 5 D 0 → 7 F 0 transition of Eu(III) for the study of its complexes that are in equi- librium in solution [9,10]. ∗ Corresponding author. Tel.: +48 61 829 1345. E-mail address: blis@amu.edu.pl (S. Lis). 2. Experimental Aqueous solutions of systems studied containing the Eu(III) ion were prepared using Eu(ClO 4 ) 3 and the appropriate amount of picolinic acid N-oxide (picNO) lig- and. The required pH values of the aqueous solutions were adjusted by additions of NaOH or HClO 4 . The concentration of Eu(III) ions was 0.02 M in all experiments. The luminescence lifetime of the Eu(III) excited state and the excitation spectra of the Eu(III) 5 D 0 → 7 F 0 transition, in the 578–581 nm region, were registered using an experimental laser system [11], consisting of a nitrogen laser and a tunable dye laser working on the P3CDOMAT dye in toluene. The Eu(III) 5 D 0 → 7 F 0 excitation spectra were measured at room temperature and liquid-nitrogen temperature. The emis- sion spectra of the solid state were recorded using a PerkinElmer spectrofluorometer MPF3. 2.1. Synthesis of Na[Eu(picNO) 4 ] complex Picolinic acid N-oxide (0.5 mmol) was completely dissolved in 5 cm 3 of distilled water by addition of NaOH to form a clear solution, to which 5cm 3 of Eu(ClO 4 ) 3 (0.1 mmol) solution was added with stirring. The resultant solution was filtered off. Storage of the solution in a desiccator charged with drierite for several days’ yielded crystals of the complex. 2.2. X-ray crystallographic study Data collections were performed by ω-scan technique in the  range 2–25 ◦ on a KUMA KM4CCD [12] four-circle diffractometer with CCD detector, using graphite-monochromated Mo K radiation ( = 0.71073 Å). Data were corrected for Lorentz-polarization effects and for absorption [13]. The structures were solved by direct methods with SIR-92 [14] and refined with SHELXL-97 [15]. Non-hydrogen atoms were refined anisotropically, hydrogen atoms were found in the difference Fourier maps and freely refined in 3 and 5, in all other structures they were placed geometrically and refined as ‘riding model’, with U is o’s set at 1.2 times Ueq of appro- priate carrier atoms. The hydrogen atoms from water molecules were found in F maps and refined with constrainted O–H distances. Relevant crystallographic data are listed in Table 1. 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.08.089