Poly[[[diaquasodium]-μ3-5-carboxy-2-ethyl-1H-imidazole-4-carboxylato-κ4 N 3,O 4:O 5:O 5] monohydrate]

In the title complex, {[Na(C7H7N2O4)(H2O)2]·H2O}n, the NaI atom exhibits a distorted octahedral geometry and is six-coordinated in an NO5 environment. The equatorial plane is defined by three O atoms and one N atom from two distinct 5-carboxy-2-ethyl-1H-imidazole-4-carboxylate (H2EIDC) ligands and one coordinated water molecule, and the apical sites are occupied by one carboxyl O atom from one H2EIDC ligand and one O atom from the other coordinated water molecule. The NaI atoms are linked by H2EIDC ligands, generating an infinite double chain along the a axis. These chains are further connected via O—H⋯O and N—H⋯O hydrogen bonds into a three-dimensional supramolecular network.

In the title complex, {[Na(C 7 H 7 N 2 O 4 )(H 2 O) 2 ]ÁH 2 O} n , the Na I atom exhibits a distorted octahedral geometry and is sixcoordinated in an NO 5 environment. The equatorial plane is defined by three O atoms and one N atom from two distinct 5-carboxy-2-ethyl-1H-imidazole-4-carboxylate (H 2 EIDC) ligands and one coordinated water molecule, and the apical sites are occupied by one carboxyl O atom from one H 2 EIDC ligand and one O atom from the other coordinated water molecule. The Na I atoms are linked by H 2 EIDC ligands, generating an infinite double chain along the a axis. These chains are further connected via O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds into a three-dimensional supramolecular network.

Comment
The rational design and synthesis of novel metal-coordination complexes via deliberate selection of metal ions and organic ligands has attracted much attention due to the fascinating structures that can be obtained and their potential applications in catalysis, magnetism, photoluminescence and gas storage (Sava et al.,2009;Lu et al., 2010;Xue et al., 2009). The 4,5imidazoledicarboxylic acid (H 3 IDC) ligand exhibits flexible multi-functional coordination sites involving two N atoms of the imidazole ring and four carboxyl O atoms, and has been widely used to construct novel supramolecular architectures (Zou et al., 2006;Li et al., 2006;Sun et al., 2005). To augment the data for the well studied H 3 IDC ligand, we recently chose to study a closely related ligand, 2-ethyl-1H-imidazole-4,5-dicarboxylic acid (H 3 EIDC) with an ethyl substitutent in the 2-position of the imidazole group, which could be a good candidate for generating intriguing supramolecular networks.
To the best of our knowledge, only a few coordination polymers based on the H 3 EIDC ligand have been reported so far (Wang et al., 2008;Zhang et al., 2010). We report herein the hydrothermal synthesis and crystal structure of a new Na I complex, the title compound.
As illustrated in Fig. 1, the title complex, [Na(C 7 H 7 N 2 O 4 ) 2 (H 2 O) 2 ].H 2 O, comprises one H 2 EIDC ligand, one Na I ion, two coordinated water molecules and one solvent water molecule. Each Na I cation exhibits a distorted octahedral geometry and is six-coordinated by three oxygen (O4, O1 i and O4 ii ) atoms and one nitrogen (N i ) atom of three distinct H 2 EIDC ligands and two oxygen atoms (O1W and O2W) from two coordinated water molecules (symmetry codes: i = 1-x, 1-y, 1-z; ii = 2-x, 1-y, 1-z). The equatorial plane is built by the O4, O1 i , O1W and N1 i atoms and the apical positions are occupied by O2W and O4 ii . Two adjacent Na centers are bridged by two carboxyl oxygen atoms to form a Na 2 O 2 subunit with a Na-Na distance of 3.684 (2) Å, and the Na 2 O 2 subunits are linked by H 2 EIDC ligands to generate a one-dimensional double chain propagating along the a axis (Fig. 2a). The adjacent one-dimensional chains are connected into a three-dimensional supramolecular structure (Fig. 2 b) via N-H···O and O-H···O hydrogen bonds involving the uncoordinated imidazole N atoms, the uncoordinated and coordinated carboxylate O atoms from the H 2 EIDC ligands and the uncoordinated and coordinated water molecules (Table 1).

Experimental
A mixture of NaOH (0.1 mmol, 0.004 g) and 2-ethyl-1H-imidazole-4,5-dicarboxylic acid (0.5 mmol, 0.9 g) in 10 ml of H 2 O was sealed in an autoclave equipped with a Teflon liner (20 ml) and then heated to 433 K for 4 days. Colorless crystals were obtained by slow evaporation of the solvent at room temperature with a yield of 42% based on NaOH.
supplementary materials sup-2 Refinement H atoms of the water molecule were located in a difference Fourier map and refined as riding with an O-H distance restraint of 0.84 (1) Å, with U iso (H) = 1.5 U eq . The H···H distances within the water molecules were restraint to 1.39 (1) Å. Carboxyl H atoms were located in a difference map but were refined as riding on the parent O atoms with O-H = 0.82 Å and U iso (H) = 1.5 U eq (O). Carbon and nitrogen bound H atoms were placed at calculated positions and were treated as riding on the parent C or N atoms with C-H = 0.96 (methyl), 0.97 (methylene) and N-H = 0.86 Å, U iso (H) = 1.2 or 1.5 U eq (C, N). Fig. 1. The structure of the title compound, showing the atomic numbering scheme. Non-H atoms are shown with 30% probability displacement ellipsoids. (symmetry codes: i = 1-x, 1-y, 1-z; ii = 2-x, 1-y, 1-z).  Crystal data [Na(C 7  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 Rfactors(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.