4-Chloroanilinium hydrogen oxalate hemihydrate

In the title hydrated molecular salt, C6H7ClN+·C2HO4 −·0.5H2O, the water O atom lies on a crystallographic twofold axis. In the crystal, the anions are linked by O—H⋯O hydrogen bonds, forming chains propagating along the b axis. These chains are interconnected through O—H⋯O hydrogen bonds from the water molecules and N—H⋯O hydrogen bonds from the cations, building layers parallel to the ab plane.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HB5378).

4-Chloroanilinium hydrogen oxalate hemihydrate
H. Rahmouni, W. Smirani, M. Rzaigui and S. S. Al-Deyab Comment Hydrogen bonding is by far the most well-studied interaction which is employed to control the conformational and topological features of the molecular assembly in the solid state (Subramanian, S. & Zawarotko, J., 1994) . In this paper, we report the synthesis and the X-ray study of the title compound, (I), a new oxalate of para-chloroanilinium hemi-hydrate,

Experimental
An ethanolic solution of p-chloroaniline (50 mmol, in 50 ml) was added under stirring to 100 ml of an aqueous solution of oxalate acid (1 M). Pink blocks of (I) appeared after few days of evaporation at room temperature.

Refinement
All H atoms were positioned in a difference map and refined on the bond lengths and angles to regularize their geometry  Fig. 1. The molecular structure of (I) with displacement ellipsoids for non-H atoms drawn at the 30% probability level. Fig. 2. A perspective view of packing of (I).

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 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.