Poly[[aqua(μ2-oxalato)(μ2-2-oxidopyridinium-3-carboxylato)dysprosium(III)] monohydrate]

In the title complex, {[Dy(C6H4NO3)(C2O4)(H2O)]·H2O}n, the DyIII ion is coordinated by seven O atoms from two 2-oxidopyridinium-3-carboxylate ligands, two oxalate ligands and one water molecule, displaying a distorted bicapped trigonal-prismatic geometry. The carboxylate groups of the 2-oxidopyridinium-3-carboxylate and oxalate ligands link dysprosium metal centres, forming layers parallel to (100). These layers are further connected by intermolecular O—H⋯O hydrogen-bonding interactions involving the coordinated water molecules, forming a three-dimensional supramolecular network. The uncoordinated water molecule is involved in N—H⋯O and O—H⋯O hydrogen-bonding interactions within the layer.

In the title complex, {[Dy(C 6 H 4 NO 3 )(C 2 O 4 )(H 2 O)]ÁH 2 O} n , the Dy III ion is coordinated by seven O atoms from two 2-oxidopyridinium-3-carboxylate ligands, two oxalate ligands and one water molecule, displaying a distorted bicapped trigonal-prismatic geometry. The carboxylate groups of the 2-oxidopyridinium-3-carboxylate and oxalate ligands link dysprosium metal centres, forming layers parallel to (100). These layers are further connected by intermolecular O-HÁ Á ÁO hydrogen-bonding interactions involving the coordinated water molecules, forming a three-dimensional supramolecular network. The uncoordinated water molecule is involved in N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen-bonding interactions within the layer.

S1. Comment
Molecular self-assembly of supramolecular architectures has received much attention during recent decades (Zeng et al., 2007;Moulton & Zaworotko, 2001). The structures and properties of such systems depend on the coordination and geometric preferences of both the central metal ions and the bridging building blocks, as well as the influence of weaker non-covalent interactions, such as hydrogen bonds and π-π stacking interactions. Recently, we obtained the title coordination polymer, which was synthesized under hydrothermal conditions.
In the structure of the title compound, each Dy III centre is in a bicapped trigonal prismatic geometry, defined by seven oxygen atoms from two 2-oxidopyridinium-3-carboxylate ligands, one oxalate ligand, and one water molecule Fig. 1. The Dy III ions are linked by 2-oxidopyridinium-3-carboxylate ligands and oxalate ligands to form a layer in the bc plane, and the adjacent Dy···Dy separations are 5.858 (4), 6.186 (5) and 6.239 Å, respectively. The layers are further connected by ιntermolecular O-H···O hydrogen bonding interactions inolving the coordinated water molecules to form a threedimensional supramolecular network (Table 1, Fig. 2). Within each layer, free water molecules further link the complexes through N-H···O and O-H···O bonding interactions (Table 1).

S2. Experimental
A mixture of Dy 2 O 3 (0.375 g; 1 mmol), 2-oxynicotinic acid (0.127 g; 1 mmol), oxalic acid (0.09 g; 1 mmol), water (10 ml) in the presence of HNO 3 (0.024 g; 0.385 mmol) was stirred vigorously for 20 min and then sealed in a Teflon-lined stainless-steel autoclave (20 ml, capacity). The autoclave was heated and maintained at 446 K for 2 days, and then cooled to room temperature at 5 K h -1 and obtained the colorless block crystals.

S3. Refinement
Water H atoms were tentatively located in difference Fourier maps and were refined with distance restraints of O-H = 0.85 Å and H···H = 1.39 Å, and with U iso (H) = 1.5 U eq (O), and then were treated as riding mode. H atoms attached to C and N atoms were placed at calculated positions and were treated as riding on their parent atoms with C-H = 0.93 Å, and N-H= 0.86Å with U iso (H) = 1.2 U eq (C,N).  The molecular structure showing the atomic-numbering scheme. Displacement ellipsoids drawn at the 30% probability level. Symmetry codes:

Figure 2
A view of the three-dimensional supramolecular network. Hydrogen bonds are shown as dashed lines. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 2.29 e Å −3 Δρ min = −1.55 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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.