3-(Benzimidazolium-2-yl)propionate dihydrate

In the crystal struture of the title compound, C10H10N2O2·2H2O, the component species are linked to the water molecules by N—H⋯O and O—H⋯O hydrogen bonds to form a three-dimensional network structure.

In the crystal struture of the title compound, C 10 H 10 N 2 O 2 Á2H 2 O, the component species are linked to the water molecules by N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds to form a three-dimensional network structure.
The crystal structure of the title compound ( Fig. 1) consists of a 3-(1H-benzo[d]imidazol-2-yl) propanoic acid organic molecule and two lattice water molecules. the dihedral angle between the benzene ring (C1,C2,C3,C4,C5,C6) and the im- forms intermolecular H bonds whereas the protonated N1 and N2 atoms act as hydrogen-bond donors and the O1 and O2 atoms act as hydrogen-bond acceptors, the O-H···O hydrogen bonds are also observed between the water molecules O2W and O1W (Table 1). these contacts and the cross-linking interactions stabilize the crystal packing.

Experimental
The propionic anhydride (13 g, 0.1 mol) was dissolved in hot water (100 ml) with stirring, and a warm solution of 1,2diaminobenzene(10.8 g, 0.1 mol) in 1,4-dioxane (100 ml) was added, following by the addition of ployphosphoric acid (50 ml) as catalyst. The mixture was refluxed for 8 h and then cooled, the solution was filtered and the filtrate was set aside for three weeks to obtain colorless crystals.

Refinement
Water H atoms were located in a difference Fourier map and refined as riding in their as-found positions relative to O atoms with U iso (H) = 1.2U eq (O). All other H atoms were placed in calculated positions and refined as riding, with C-H = 0.93-0.97 Å, N-H = 0.86 Å, and U iso (H) = 1.2-1.5 U eq (C,N). Fig. 1. The molecular structure of (I) showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.

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 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.