4-[(4-Aminophenyl)sulfonyl]aniline–3,5-dinitrobenzoic acid (1/1)

The title compound, C7H4N2O6·C12H12N2O2S, is a 1:1 cocrystal of the drug dapsone with 3,5-dinitrobenzoic acid. The dihedral angle between the two aromatic rings of the dapsone molecule is 75.4 (2)°, and the dihedral angles between these rings and that of the 3,5-dinitrobenzoic acid are 64.5 (2) and 68.4 (2)°. A strong intermolecular carboxylic acid O—H⋯Namine hydrogen bond is found, together with intermolecular amine N—H⋯O hydrogen-bonding associations with carboxyl, nitro and sulfone O-atom acceptors. In addition, weak π–π interactions between one of the dapsone benzene rings and the 3,5-dinitrobenzoic acid ring [ring centroid separation = 3.774 (2) Å] results in a two-dimensional network structure.

The title compound, C 7 H 4 N 2 O 6 ÁC 12 H 12 N 2 O 2 S, is a 1:1 cocrystal of the drug dapsone with 3,5-dinitrobenzoic acid. The dihedral angle between the two aromatic rings of the dapsone molecule is 75.4 (2) , and the dihedral angles between these rings and that of the 3,5-dinitrobenzoic acid are 64.5 (2) and 68.4 (2) . A strong intermolecular carboxylic acid O-HÁ Á ÁN amine hydrogen bond is found, together with intermolecular amine N-HÁ Á ÁO hydrogen-bonding associations with carboxyl, nitro and sulfone O-atom acceptors. In addition, weakinteractions between one of the dapsone benzene rings and the 3,5-dinitrobenzoic acid ring [ring centroid separation = 3.774 (2) Å ] results in a two-dimensional network structure.

Graham Smith and Urs D. Wermuth Comment
Dapsone [4-(4-aminophenylsulfonyl)aniline] is a very weak Lewis base which finds use as an anti-leprotic, anti-malarial and leprostatic drug (Wilson et al., 1991). The structure of the Dapsone 0.33hydrate is known (Kus'mina et al., 1981) but salts or adducts of this compound are not common. We have reported the 1:2 co-crystalline adduct with 1,3,5-trinitrobenzene (Smith & Wermuth, 2012a). Reported here is the structure of the 1:1 cocrystalline adduct of Dapsone with 3,5dinitrobenzoic acid, C 12 H 12 N 2 O 2 S. C 7 H 4 N 4 O 6 ( Fig. 1). This acid has been found to be very useful for the formation of cocrystalline adducts (Etter & Frankenbach, 1989).
A primary intermolecular O-H···O amine hydrogen bond (Table 1) links the two molecules while N-H···O hydrogenbond associations with carboxyl, nitro and sulfone O-atom acceptors give a two-dimensional structure (Fig. 2). A weak π-π interaction is also found between one of the Dapsone aromatic ring moieties (C1-C6) and that of the acid molecule

Experimental
The title compound was prepared by the intereaction of 4-(4-aminophenylsulfonyl)aniline (Dapsone) with 3,5-dinitrobenzoic acid by heating together for 15 min under reflux, 1 mmol quantities of the two reagents in 50 ml of 50% ethanolwater. Minor poorly-formed yellow crystal aggregates of the title co-crystal formed after partial room-temperature evaporation of the solvent.

Refinement
All H atoms potentially involved in hydrogen-bonding associations were located in a difference-Fourier analysis but were subsequently constrained, with U iso (H) = 1.2U eq (N, O). Other H-atoms were included at calculated positions [C-H = 0.93 Å] and also treated as riding, with U iso (H) = 1.2U eq (C). No reasonable acceptor atom could be found for one of the amine H-atoms on N4 (H411).  The molecular conformation and atom-numbering scheme for the Dapsone and 3,5-dinitrobenzoic acid molecules in the title co-crystal. Non-H atoms are shown as 50% probability displacement ellipsoids and the inter-species hydrogen bond is shown as a dashed line.

Figure 2
The hydrogen-bonding in the title adduct, viewed down the a axial direction of the unit cell. Hydrogen bonds are shown as dashed lines. For symmetry codes see Table 1.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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.