Poly[[triaqua(μ3-pyridine-2,4,6-tricarboxylato)gadolinium(III)] monohydrate]

The title compound, {[Gd(C8H2NO6)(H2O)3]·H2O}n, was obtained in water under hydrothermal conditions. The GdIII ions are nine-coordinated by two O and one N atoms from one pyridine-2,4,6-tricarboxylate ligand, two O atoms from another ligand, one O atom from a third ligand and three coordinated water molecules. Each ligand binds three metal centers. Two-dimensional layers are formed through the Gd—O bonds and the layers are linked by O—H⋯O hydrogen bonds, forming a three-dimensional network.

The title compound, {[Gd(C 8 H 2 NO 6 )(H 2 O) 3 ]ÁH 2 O} n , was obtained in water under hydrothermal conditions. The Gd III ions are nine-coordinated by two O and one N atoms from one pyridine-2,4,6-tricarboxylate ligand, two O atoms from another ligand, one O atom from a third ligand and three coordinated water molecules. Each ligand binds three metal centers. Two-dimensional layers are formed through the Gd-O bonds and the layers are linked by O-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.

S1. Comment
The preparation and property researching of metal-organic frameworks have attracted widespread interest in recent years due to their potential application in the areas of magnetism, luminescence, adsorption, catalysis and so on (Parker, 2000;Tobisch, 2005;Pan et al., 2003). Multicarboxylic acids containing pyridyl rings were widely used and many 1-D, 2-D and 3-D coordination polymers with novel structures have been reported. Especially, complexes with pyridine-2,4,6-tricarboxylato (H 3 pta = pyridine-2,4,6-tricarboxylic acid) ligands have been recently reported (Li et al., 2008;Wang et al., 2007;Fu et al., 2008.). The title compound is a new Gd III complex built with pta ligands and prepared under hydrothermal conditions.
As shown in Fig. 1, the local geometry of Gd III ion is a distorted monocapped antitetragonal prism. Each pta ligand connects three Gd III ions with oxgen atoms of the carboxyl groups and the nitrogen atom. There are three coordination water molecules on each Gd III ion. A two-dimentional layer is constructed by the bonding among oxygen atoms and Gd III ions (see Fig. 2). In addition, a lattice water molecule per asymmetric unit is in the crystal structure. Many O-H···O hydrogen bonds are formed between the oxygen atoms of water molecules and the oxygen atoms of caboxyl groups. As a result, the three-dimensional network formed by hydrogen bonds is shown in Fig. 3.

S3. Refinement
All hydrogen atoms bonded to carbon atoms were positioned geometrically and refined as riding, with C-H = 0.95 Å and U iso (H) = 1.2U eq (C). The H atoms of water molecules were found from difference Fourier maps and included in the  The molecular structure of (I), with atom labels and 30% probability displacement ellipsoids for non-H atoms.

Figure 2
The packing of (I), showing the two-dimensional layers formed by Gd-O bonds.  View of the three-dimensional network constructed by O-H···O hydrogen bonds (dashed lines). All H atoms were omitted for clarity.

Poly[[triaqua(µ 3 -pyridine-2,4,6-tricarboxylato)gadolinium(III)] monohydrate]
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.64 e Å −3 Δρ min = −1.29 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.