4,4′-Methylenedianilinium bis(3-carboxy-4-hydroxybenzenesulfonate) monohydrate

Co-crystallization of 4,4′-methylenediphenylamine (MDA) and 5-sulfosalicylic acid (5-H2SSA) yields the title salt, C13H16N2 2+·2C7H5O6S−·H2O. The asymmetric unit is comprised of one dication, two anions and one water molecule. In the crystal structure, the components of the salt are linked by a combination of intermolecular O—H⋯O, N—H⋯O and weak C—H⋯O hydrogen bonds into a three-dimensional framework. In addition, two weak π–π interactions [with centroid–centroid distances of 3.8734 (15) and 3.7465 (15) Å] and one C—H⋯π interaction further stabilize the crystal structure.


Related literature
For related structures, see: Smith (2005); Smith et al. (2005a,b, 2006). For background information, see: Wang et al. (2008). In a continuation of our studies on the molecular and supra-molecular structures in organic salts formed by 5sulfosaliyclic acid (5-H 2 SSA) and N-containing lewis bases (Wang et al., 2008), we now report our findings on the title compound (Scheme I).

S2. Experimental
All reagents and solvents were used as obtained without further purification. Equivalent molar amount of 4,4′-methylenediphenylamine and 5-sulfosalicylic acid dihydrate were dissolved in 95% methanol (20 ml). The mixture was stirred for 30 minutes at 300 K and then filtered. Colorless plate crystals of (I) suitable for single-crystal X-ray diffraction analysis grew at the bottom of the vessel in two weeks after slow evaporation of the solution.

S3. Refinement
The title compound is racemic in solution but spontaneously resolved upon crystallization. The absolute configuration of the molecules in the crystal selected was readily determined and the configuration has no chemical significance.
H atoms bonded to C atoms were positioned geometrically with C-H = 0.93 Å (aromatic), 0.97 Å (methylene) and refined in a riding mode [U iso (H) = 1.2U eq (C)]. H atoms bonded to N and O atoms were found in difference maps and the N-H and O-H distances were refined freely [the refined distances are given in Table 1; U iso (H) = 1.2U eq (N) and 1.5U eq (O), respectively].

Figure 2
Part of the crystal structure of (I), showing the formation of the three-dimensional framework structure. Hydrogen bonds are shown as dashed lines. For the sake of clarity, H atoms not involved in the motif have been omitted from the drawing.

4,4′-Methylenedianilinium bis(3-carboxy-4-hydroxybenzenesulfonate) monohydrate
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.33 e Å −3 Δρ min = −0.17 e Å −3 Absolute structure: Flack (1983), 3009 Friedel pairs Absolute structure parameter: 0.05 (6) 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 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.