Bis(4-sulfamoylanilinium) sulfate

In the title salt, 2C6H9N2O2S+·SO4 2−, the sulfate S atom is situated on a crystallographic twofold axis (the symmetry of the anion is 2). The anion exerts intense libration, which is manifested by shortening of the observed sulfate S—O bonds, as well as by features in the electron-density map. The crystal structure is stabilized through a three-dimensional hydrogen-bonding network formed by strong N—H⋯O hydrogen bonds.

In the title salt, 2C 6 H 9 N 2 O 2 S + ÁSO 4 2À , the sulfate S atom is situated on a crystallographic twofold axis (the symmetry of the anion is 2). The anion exerts intense libration, which is manifested by shortening of the observed sulfate S-O bonds, as well as by features in the electron-density map. The crystal structure is stabilized through a three-dimensional hydrogenbonding network formed by strong N-HÁ Á ÁO hydrogen bonds.
Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXTL/PC (Sheldrick, 2008); program(s) used to refine structure: SHELXTL/PC and JANA2006 (Petricek et al., 2006); molecular graphics: PLATON (Spek, 2009) and JANA2006; software used to prepare material for publication: SHELXTL/PC. SPR and BRK thank the management of the Devanga Arts College for their support and encouragement and also extend their thanks to the University Grants Commission for the financial support of this work in the form of a Minor Research Project.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FB2278). Sulfanilamides, which belong to sulfonamide drugs, act as competitive inhibitors for the enzyme dihydropteroate synthetase (DHPS). This enzyme is involved in the folate synthesis (Kent, 2000).
We have recently reported a nitrate complex of sulfanilamide (Pandiarajan et al., 2011). In continuation of our interest on the sulfanilamide complexes, the synthesis of the title compound and its title structure, bis(4-sulfamoylanilinium) sulfate, is described here.
In the title structure, the sulfate anion is situated in the special position on the twofold axis, thus the symmetry of this molecule is 2. The refinement has shown that the displacement ellipsoid of the sulfate atom O22 is extensively elongated while that of O21 has shown usual behaviour (Fig. 1). This is due to the libration movement as it is indicated by Figs. 2 and 3 which show the sections of the electron density maps (Petricek et al., 2006) through S2 and the atoms O21 and O22, respectively. Note the curved electron density pertinent to O22 (Fig. 3). The libration movement is also manifested by the values of the corrected S-O distances (Nardelli, 1995): The uncorrected values S2-O21 and S2-O22 are 1.475 (2) and 1.436 (2) Å, respectively, while the respective corrected values equal to 1.501 and 1.516 Å. The attempts to express the libration of the sulfate by TLS (Schomaker & Trueblood, 1968;JANA2006 (Petricek et al., 2006 failed in this case. The geometric parameters of the cation in the title structure is in agreement with the reported structures of 4sulfamoylanilinium nitrate (Pandiarajan et al., 2011) and 4-sulfamoylanilinium chloride (Zaouali Zgolli et al., 2010).
The crystal structure is stabilized through a three-dimensional hydrogen bonding network formed by strong N-H···O hydrogen bonds (Table 1, Fig. 4). (The nomenclature regarding the strength of the hydrogen bonds was taken from Desiraju & Steiner, 1999.) The sulfate oxygens as well as the oxygen O2 of the sulfonamyl group are the acceptors of these strong hydrogen bonds (Table 1) which are donated by the primary amine as well as by the ammonium groups.
Among the important graph set motifs pertinent to the hydrogen bonding in the structure can be named R 2 2 (16) (Etter et al., 1990): The cationic -NH 3 group is bonded to the O atom of the S═O group of another cation through the N2-H2B···O2 iii hydrogen bond (the symmetry code iii: -x, 1-y, 1-z). These bonds are involved in a ring motif R 2 2 (16) about the crystallographic inversion centre situated at the Wyckoff position 4a. Among other graph-set motifs which can be discerned in this hydrogen bond pattern, C 4 4 (12) is worthwhile mentioning.

Experimental
The synthesis of the title compound was carried out by heating of the mixture of sulphanilamide (3.4 g) and sulfuric acid (0.5 ml of 98% concentration) in 20 ml of water as the stoichiometric ratio of 2:1 (at 60°C) under reflux for 1 h.
Colourless prismatic crystals of bis(4-sulfamoylanilinium) sulfate suitable for single-crystal X-ray analysis with the approximate size of 1.6 cm × 0.8 cm × 0.3 cm were obtained by slow evaporation at room temperature. The measured sample was cut from a bigger crystal.

Refinement
All the H atoms were discernible in the difference electron density map. Nevertheless, the aryl H atoms were constrained and refined in the riding atom approximation: C aryl -H aryl = 0.93 Å and U iso (H aryl )= 1.2U eq (C aryl ). The other atoms are involved in the N-H···O hydrogen bonds and after some tests also the ammonium H atoms were constrained in idealized tetrahedral symmetry because a distance-restrained refinement yielded improbable differences in N2-H2A, N2-H2B, N2-H2C distances. The pertinent constraints were N2-H ammonium = 0.89 Å and U iso (H ammonium )= 1.5U eq (N ammonium ). The distances of the primary amine H atoms to their carrier atom N1 were restrained to 0.86 (1) Å while the U iso (H amine )= 1.2U eq (N amine ).

Figure 1
The title molecule with the atom numbering scheme. The displacement ellipsoids are shown at the 50% probability level.  Section through the electron density map calculated from F o passing through the atoms S2 and the atoms O21 and O21 i (Petricek et al., 2006). Symmetry code: (i) 1-x, y, 3/2-z. The contours are given in 1 eÅ -3 levels.  Section through the electron density map calculated from F o passing through the atoms S2 and the atoms O22 and O22 i (Petricek et al., 2006). Symmetry code: (i) 1-x, y, 3/2-z. The contours are given in 1 eÅ -3 levels. The curved character of the electron density of the depicted O atoms indicates libration movement.  Δρ max = 0.69 e Å −3 Δρ min = −0.51 e Å −3 Extinction correction: SHELXTL/PC (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.048 (2) 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 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. Symmetry codes: (i) −x+1, y, −z+3/2; (ii) −x+1/2, y+1/2, z; (iii) −x, −y+1, −z+1; (iv) x, −y+1, z−1/2; (v) x−1/2, −y+3/2, −z+1; (vi) −x+1, −y+1, −z+1.