Expected and unexpected products of reactions of 2-hydrazinylbenzothiazole with 3-nitrobenzenesulfonyl chloride in different solvents

Two compounds arose from the same reaction in methanol and the other arose from an unexpected reaction with the acetone solvent.


Chemical context
Heteroaromatic benzothiazole derivatives are well-studied compounds, due in the main to their various and useful biological activities (for a review, see Gulati et al., 2017), but also to their fluorescent and optical properties (e.g. Liu et al., 2018). Hydrazonyl derivatives, 2-Ar-CH N-NH-benzothiazoles, formed from 2-hydrazinylbenzothiazole and ArCHO have attracted attention: for example, Katava et al. (2017) have reported antitumor activities and Behera & Manivannan (2017) studied their use as sensors. Less attention has been paid generally to 2-(ArSO 2 NHNH)-benzothiazoles, although antimicrobial activities have been briefly reported (Rao et al., 2005;Hipparagi et al., 2007).

Structural commentary
Compound (I) crystallizes in space group P1 with one C 10 H 12 N 3 S + cation (protonated at N1) and one C 6 H 4 NO 5 S À sulfonate anion in the asymmetric unit (Fig. 1). Evidently, the starting hydrazone has reacted with the acetone solvent (Day & Whiting, 1970) to generate an N-propylidine group; at the same time, the sulfonyl chloride has been hydrolysed to sulfonic acid and a molecular salt has crystallized after proton transfer from the sulfonic acid to the N atom of the thiazole ring. The cation is close to planar; the dihedral angle between the benzothiazole ring system (r.m.s. deviation = 0.005 Å ) and the N2/N3/C8/C9/C10 grouping (r.m.s. deviation = 0.004 Å ) is 7.89 (10) ; the C7-N2-N3-C8 torsion angle is À172.8 (2) .
The C8-N3 bond length of 1.278 (4) Å is fully consistent with double-bond character. In the anion, the nitro group is twisted by 26.7 (4) with respect to the benzene ring. As expected, the S-O bond lengths of the sulfonate group are almost the same, indicating the usual delocalization of the negative charge and the same situation is found in compound (III) described below.
Compound (II) represents the expected condensation product of the starting hydrazone and sulfonyl chloride and crystallizes with two neutral C 13 H 10 N 4 O 4 S molecules in the asymmetric unit (Fig. 2) in space group P1. In the first (S1) molecule, the dihedral angle between the benzothiazole ring system (r.m.s. deviation = 0.013 Å ) and the C8 benzene ring is 32.59 (4) ; the nitro group is twisted by 0.68 (7) from the C8 benzene ring. The C7-N2-N3-S2 torsion angle is À99.88 (12) and the H2-N2-N3-H3 torsion angle is À54 (2) . The bond-angle sum at N2 is 359.9 , indicative of sp 2 hybridization, whereas the corresponding value for N3 of 341.1 points towards substantial sp 3 hybrid character. The C7-N2 bond length of 1.3529 (16) Å is short for a nominal single bond, presumably indicative of conjugation of the N2 nominal lone pair of electrons with the adjacent ring system. In the second (S3) molecule, the corresponding geometrical 674 Morscher et al. C 10 H 12 N 3 S + ÁC 6 H 4 NO 5 S À and two related compounds The asymmetric unit of (II) showing 50% displacement ellipsoids. Hydrogen bonds are indicated by double-dashed lines.

Figure 1
The asymmetric unit of (I) showing 50% displacement ellipsoids. Hydrogen bonds are indicated by double-dashed lines.
Compound (III), which was recovered from the same reaction as (II), represents the same condensation product, which has gone on to further react with a hydrolysed sulfonyl chloride species to form a molecular salt (proton transfer to N1). Once again, the space group is P1 and one cation and one anion (Fig. 3) make up the asymmetric unit. The benzothiazole ring system (r.m.s. deviation = 0.005 Å ) subtends a dihedral angle of 57.54 (3) with the C8 benzene ring and the nitro group is twisted from its attached ring by 4.8 (3) . The C7-N2-N3-S2 and H2-N2-N3-H3 torsion angles are À110.54 (12) and À48.5 (19) , respectively. The bond-angle sums at N2 and N3 are 359.0 and 339.1 , respectively, and the same conclusions re hybridization states for these atoms as in (II) may be drawn. This is backed up by the shortened C7-N2 bond length of 1.3317 (17) Å in (III) compared to (II). presumably because resonance is enhanced by the positive charge on N1. In the anion, the nitro group is twisted from its attached ring by 17.7 (2) .

Supramolecular features
In the crystal of (I), the cation and the anion are linked by a pair of N-HÁ Á ÁO hydrogen bonds (Table 1), which generate an R 2 2 (8) loop. The ion pairs are connected by various weak C-HÁ Á ÁO interactions, with the acceptor O atoms being parts of the sulfonate and nitro groups. No C-HÁ Á Á interactions could be identified in the crystal of (I) but aromaticstacking interactions are seen, with the shortest centroidcentroid separation of 3.4274 (18) Å (slippage = 0.729 Å ) occurring between inversion-related pairs of thiazole rings (Fig. 4); atom N2 of the hydrazone group lies above the benzene ring (CgÁ Á ÁN2 = 3.385 Å ) and possibly provides some additional stabilization. Taken together, the directional inter-molecular interactions in (I) generate a three-dimensional network.
tetramer (two cations and two anions) results (Fig. 6). A pair of weak C-HÁ Á ÁO interactions helps to provide cohesion between tetramers in the crystal andstacking is also observed, with the shortest centroid-centroid separation being 3.6743 (8) Å between the thiazole and C1-C6 rings.

Synthesis and crystallization
To prepare (I), a mixture of 2-hydrazinylbenzothiazole (1.00 mmol) and 3-nitrobenzenesulfonyl chloride (1.00 mmol) in acetone (15 ml An inversion-generated tetramer in the crystal of (III). Symmetry code: (i) 1 À x, 1 À y, Àz. 6. Refinement Crystal data, data collection and structure refinement details are summarized in Table 4. The N-bound hydrogen atoms were located in difference maps and their positions freely refined. The C-bound hydrogen atoms were geometrically placed (C-H = 0.95-0.98 Å ) and refined as riding atoms. The constraint U iso (H) = 1.2U eq (carrier) or 1.5U eq (methyl carrier) was applied in all cases. The methyl groups in (I) were allowed to rotate, but not to tip, to best fit the electron density.  For all structures, data collection: CrystalClear (Rigaku, 2012); cell refinement: CrystalClear (Rigaku, 2012); data reduction: CrystalClear (Rigaku, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: publCIF (Westrip, 2010).  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.

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.  (12) C18-C19-C14 121.70 (12) C5-C6-S1