5-Carboxy-2-isopropyl-1H-imidazol-3-ium-4-carboxylate monohydrate

In the title compound, C8H10N2O4·H2O, the imidazole N atom is protonated and one of the carboxylate groups is deprotoned, forming a zwitterion. An intramolecular O—H⋯O hydrogen bond occurs. The crystal structure is stabilized by intermolecular N—H⋯O and O—H⋯O hydrogen bonds. In addition, intermolecular N—H⋯O and O—H⋯O hydrogen bonds link the molecules into two-dimensional networks parallel to (10).

In the title compound, C 8 H 10 N 2 O 4 ÁH 2 O, the imidazole N atom is protonated and one of the carboxylate groups is deprotoned, forming a zwitterion. An intramolecular O-HÁ Á ÁO hydrogen bond occurs. The crystal structure is stabilized by intermolecular N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds. In addition, intermolecular N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds link the molecules into two-dimensional networks parallel to (102).

Comment
In the past the construction of metal complexes based on N-heterocyclic carboxylic acids has attracted much attention due to their intriguing topologies as well as their potential applications in many fields. Particular attention has been paid to the 1Himidazole-4,5-dicarboxylic acid ligand and its analogs: (Sun et al., 2006) have synthesized the 4-carboxy-2-(pyridinium-4yl)-1H-imidazole-5-carboxylate monohydrate; Merchan et al. (2007) have prepared the dimethylammonium 4-carboxy-1Himidazole-5-carboxylate; (Guo, 2009) have reported the 4-carboxy-2-methyl-1H-imidazole-5-carboxylate monohydrate and (Wang & Qin, 2010) have reported the dimethylammonium 4-carboxy-2-n-propyl-1H-imidazole-5-carboxylate. All of these 1H-imidazole-4,5-dicarboxylic acid and their analogs have been used as ligands to design metal complexes and most of them are proved ideal ligands Feng et al., 2010;Li et al., 2010). However, the crystal structure of 4-carboxy-2-isopropyl-1H-imidazole-5-carboxylate has not been yet determined. Keeping that in mind, we report here the preparation and crystal structure of the title compound. The crystal structure (Fig.2, Table1) is stabilized by two intramolecular and three intermolecular N-H···O and O-H···O hydrogen bonds which link the molecules into two-dimensional networks parallel to the (102) planes.

Experimental
The title compound was synthesized according to the method reported in the literature (Alcalde et al., 1992). Colourless single crystals suitable for X-ray diffraction were obtained by slow evaporation of a water solution of the compound.

Refinement
H atoms bonded to the water O atom were located in an electron density map and refined with distance restraints of O-H = 0.85 Å. Other H atoms were positioned geometrically and refined using a riding model, with C-H = 0.96-0.98 Å, N-H = 0.86 Å and O-H = 0.82 Å. U iso (H) = kU eq (carrier atom), where k = 1.2 for N and C tertiary and 1.5 for O and C methyl . Fig. 1

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 ofF 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.