(E)-4-[4-(Diethylamino)benzylideneammonio]benzenesulfonate

The title compound, C17H20N2O3S, synthesised from sulfanilic acid and 4-diethylaminobenzaldehyde, crystallized out as a zwitterion with the central N atom protonated. The zwitterion exists in an E conformation with respect to the C=N double bond. The dihedral angle between the benzene rings is 37.57 (5)°. In the crystal, the zwitterions are linked into a tape along the a axis by N—H⋯O hydrogen bonds. The crystal structure is further stabilized by weak C—H⋯O interactions and π–π interactions with a centroid–centroid distance of 3.8541 (6) Å. An O⋯O [2.8498 (11) Å] short contact is present.


(E)-4-[4-(Diethylamino)benzylideneammonio]benzenesulfonate Pumsak Ruanwas, Suchada Chantrapromma and Hoong-Kun Fun Comment
Benzenesulfonic acid is a very strong acid and coupled with aromatic components are interesting chemical reagents (King, 1991). Many of these combinations exhibit pharmaceutical and biological activities (Chanawanno et al., 2010;Taylor et al., 2006) and were also used as whitening reagents (Hussain et al., 2009) and fluorescence sensors (Kim et al., 2011). The title compound (I) was synthesized on account of its fluorescence property. It was found that (I) shows solid state fluorescence with the maximum emission at 625 nm when was excited at 400 nm. Herein the synthesis and crystal structure of (I) are reported.
In Fig. 1, the molecule of (I), C 17 H 20 N 2 O 3 S, crystallized out as a zwitterion with the N1 atom protonated. The hydrogen is more preferably attached to the nitrogen atom due to the stronger basicity of NH 2 group compared to the SO 3 -  et al., 1987) and are comparable with the related structure (Yeap et al., 2010).

Experimental
Sulfanilic acid (0.5 g, 2.8 mmol) was dissolved in water (10 ml) and then 4-diethylaminobenzaldehyde (0.5 g, 2.8 mmol) was added. The mixture was refluxed at 120 °C for 2 h. The precipitate was filtered, washed with water and purified by recrystallization from ethanol to afford the compound I (yield 79%). Yellow block-shaped single crystals of the title compound suitable for X-ray structure determination were formed from recrystallization from ethanol by the slow evaporation of the solvent at room temperature after a week (m.p. 540-541 K).

Refinement
Amide H atom was located from a difference map and isotropically refined. The remaining H atoms were positioned geometrically and allowed to ride on their parent atoms, with d(C-H) = 0.93 Å for aromatic and CH, 0.97 Å for CH 2 and 0.96 Å for CH 3 atoms. The U iso values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl groups. program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figure 1
The molecular structure of the title compound, showing 60% probability displacement ellipsoids and the atom-numbering scheme.   (Cosier & Glazer, 1986) operating at 120.0 (1) K. 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq S1 −0.35313 (