catena-Poly[sodium [[tris(3-methylpyridine-2-carboxylato)europate(III)]-μ-3-methylpyridine-2-carboxylato] trihydrate]

In the title structure, {Na[Eu(C7H6NO2)4]·3H2O}n, the EuIII atom is nine-coordinated within a slightly distorted tricapped trigonal-prismatic coordination geometry defined by five carboxylate-O atoms and four pyridine-N atoms. One of the carboxylate ligands bridges the Eu cations, forming a one-dimensional coordination polymer along the b axis. The Eu—O bond distances lie within the range 2.362 (4)–2.461 (4) Å. In the crystal structure, intermolecular O—H⋯O hydrogen bonds link the polymers into a three-dimensional network.


S1. Comment
Metal complexes of picolinic acid and their derivatives have been of considerable interest due to their adoption of various coordination modes and their interesting photophysical properties (Seo et al., 2010;Kukovec et al., 2009;Hong et al., 2008;Soares-Santos et al., 2006). Especially, Eu(III) complexes have been extensively studied due to their unique luminescence properties such as narrow emission bands and the excitation spectra of the five-dimensional 0 -> 7F 0 transition (Lis et al., 2009;Godlewska et al., 2008;Legendziewicz et al., 2002). In this study, we report the synthesis and characterization of a Eu(III)-picolinic acid derivative in order to develop new lanthanide complexes for novel photoluminescent applications.
In the title one-dimensional coordination polymer, {Na[Eu(C 7 H 6 NO 2 ) 4 ] 3H 2 O} n , the Eu atom is nine-coordinate within a slightly distorted tricapped trigonal prismatic coordination geometry. The Eu(III) atom is coordinated to the five carboxylate-O atoms and four pyridine-N atoms. The Eu-O bond distances are within the range of 2.362 (4) -2.461 (4) Å, Table 1, which are significantly shorter than the sum of the covalent radii of Eu and O atoms (2.66 Å). The dihedral angles between the pyridine rings and the carboxylate groups are in the range of 5.0 (4) -24.7 (4) °. One of the carboxylate ligands bridges Eu cations to form a one-dimensional coordination polymer along the crystallographic b axis (Fig. 2).
Intramolecular O-H···O hydrogen bonds link the uncoordinated water molecules to the coordinated water molecules, Table 2. In the crystal structure, intermolecular O-H···O hydrogen bonds link the polymers into a three-dimensional network, Table 2. The title compound exhibits an intense emission at 618 nm upon 396 nm excitation in PL spectra with 325 nm of He-Cd laser excitation wavelength.

S2. Experimental
Europium trichloride solution was prepared by dissolving EuCl 3 6H 2 O (0.37 g, 1.0 mmol; Aldrich) in absolute ethanol (20 ml) at room temperature with stirring. The ligand solution was prepared by dissolving 3-methylpicolinic acid (0.55 g, 4.0 mmol; Aldrich) in absolute ethanol (30 ml) at room temperature. The pH of the ligand solution was adjusted to about 6 with 2 N NaOH solution. The Eu solution was added drop wise and slowly to the ligand solution. The reaction mixture was stirred for 2 h at room temperature. Colourless crystals of (I) were obtained at room temperature over a period of a few weeks. The complex was recrystallized from distilled water.

S3. Refinement
The water-H atoms were located in a difference Fourier map and refined with O-H = 0.82±0.01 Å. The remaining H atoms were positioned geometrically and refined using a riding model with C-H = 0.94 -0.97 Å, and with U iso (H) = 1.2U eq (C) for aromatic-H and 1.5U eq (C) for methyl-H atoms. The maximum and minimum residual electron density peaks of 1.77 and -1.63 eÅ -3 , respectively, were located 1.55 Å and 0.79 Å from the O39 and Eu1 atoms, respectively.   One-dimensional supramolecular chain along the b axis. H atoms have been omitted for clarity.       (2)