5-Carboxy-2,4-dihydroxyanilinium chloride dihydrate

In the title compound, C7H8NO4 +·Cl−·2H2O, the organic molecule is almost planar with an r.m.s. deviation of 0.0164 Å for all non-H atoms. An S(6) ring motif is formed due to an intramolecular O—H⋯O hydrogen bond. In the crystal, the molecules are linked into a three-dimensional network by N—H⋯Cl, N—H⋯O, O—H⋯Cl and O—H⋯O hydrogen bonds.

In the title compound, C 7 H 8 NO 4 + ÁCl À Á2H 2 O, the organic molecule is almost planar with an r.m.s. deviation of 0.0164 Å for all non-H atoms. An S(6) ring motif is formed due to an intramolecular O-HÁ Á ÁO hydrogen bond. In the crystal, the molecules are linked into a three-dimensional network by N-HÁ Á ÁCl, N-HÁ Á ÁO, O-HÁ Á ÁCl and O-HÁ Á ÁO hydrogen bonds.

Comment
Recently we have reported the crystal structure of 5-carboxy-2,4-dihydroxyanilinium chloride (Naz et al., 2010). The title compound (I, Fig. 1) has been prepared in a slightly different way.
In (I), the organic group (C1-C7/O1-O4/N1) is planar with r. m. s. deviation of 0.0164 Å. In the organic part, there exist a strong intramolecular H-bond of O-H···O type ( Table 1, Fig. 1) completing an S(6) ring motif (Bernstein et al., 1995). In the title compound, the Clanion is penta coordinated due to H-bondings of N-H···Cl and O-H···Cl types ( Table   1, Fig. 2). The NH 3 + ion makes H-bonding with the both water molecules and the Clion. Due to these strong H-bondings the molecules are stabilized in the form of three-dimensional polymeric network (Table 1, Fig. 2). There does not exist any π···π or C-H···π interaction.

Experimental
Concentrated nitric acid (2 mL, 67%) was added drop by drop to β-resorcylic acid (1 g, 97%, 6.3 mmol) in a round bottom flask. The mixture was protected from moisture by CaCl 2 (anhydrous) tube and was allowed to stand for 12 h at room temperature. Then reaction mixture was diluted with water. The crude material was filtered and recrystallized from water to affoard the 5-nitro-β-resorcylic acid.
Then a mixture of 5-nitro-β-resorcylic acid (1.5 g, 7.5 mmol), tin (3 g, 25 mmol) and absolute ethanol (5 ml) were taken in a 100 ml round bottom flask and passed HCl gas under reflux with stirring for 1 h. The completion of reaction was monitored by TLC. The reaction mixture was filtered to remove any unreacted tin. Filtrate was kept for seven days to afford light brown needles 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.