Diaquabis(4-carboxy-2-propyl-1H-imidazole-5-carboxylato-κ2 N 3,O 4)zinc(II) N,N-dimethylformamide disolvate

In the crystal structure of the title compound, [Zn(C8H9N2O4)2(H2O)2]·2C3H7NO, the ZnII atom is coordinated by two N,O-bidentate 2-propyl-1H-imidazole-4,5-dicarboxylate anions and two water molecules in a distorted octahedral environment. The asymmetric unit consists of one ZnII atom located on a center of inversion as well as one anion, one water molecule and one additional dimethylformamide molecule that occupy general positions. Between the carboxyl and the carboxylate group an intramolecular hydrogen bond is found in which the hydroxy H atom is disordered. Disorder is also found for the H atoms of one of the three methyl groups. In the crystal structure, additional intermolecular N—H⋯O and O—H⋯O hydrogen bonding is found.

In the crystal structure of the title compound, [Zn(C 8 H 9 N 2 O 4 ) 2 (H 2 O) 2 ]Á2C 3 H 7 NO, the Zn II atom is coordinated by two N,O-bidentate 2-propyl-1H-imidazole-4,5dicarboxylate anions and two water molecules in a distorted octahedral environment. The asymmetric unit consists of one Zn II atom located on a center of inversion as well as one anion, one water molecule and one additional dimethylformamide molecule that occupy general positions. Between the carboxyl and the carboxylate group an intramolecular hydrogen bond is found in which the hydroxy H atom is disordered. Disorder is also found for the H atoms of one of the three methyl groups. In the crystal structure, additional intermolecular N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonding is found.

Experimental
Crystal data [Zn(C 8 Table 1 Hydrogen-bond geometry (Å , ). Comment Imidazole-4,5-dicarboxylic acid (H 3 Imda) can be deprotonated to generate three types of anions, namely Imda 3-, HImda 2and H 2 Imdaand react with metal ions to form fascinating structures with different structures and useful properties (Maji et al., 2005;Yang & Zhang, 2006). We have therefore reacted the 2-propyl-1H -imidazole-4,5-dicarboxylic acid with Zn(NO 3 ) 2 under hydrothermal conditions to obtain a new Zn II complex and its structure is reported here. As illustrated in figure 1, the title complex molecule is a discrete complex, consisting of one Zn II ion, two mono-deprotonated 2-Propyl-1H-imidazole-4,5-dicarboxy anions and two water molecules. The Zn II atom resides on a crystallographic inversion centre and is trans-  Table 1). The crystal structure contain additional dimethylfromamide molecules that are linked to the complexes via N-H···O hydrogen bonding (Fig. 2). The complexes are additionally connected by intermolecular O-H···O hydrogen bonding between the carboxyl O atoms and the water H atoms (Table 1 and Fig. 2).

Experimental
A mixture of Zn(NO 3 ) 2 (0.2 mmol, 0.03 g) and 2-propyl-1H-imidazole-4,5-dicarboxylic acid(0.5 mmol, 0.99 g) and 10 ml of C 3 H 7 NO was loaded in a 25 ml Telflon-lined stainless steel vessel and heated at 373k for 3 days. White crystals were obtained when the sample was cooled to room temperature slowly.

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 > 2sigma(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (