(Z)-4-Hexyl-1-(5-nitro-2-oxo-2,3-dihydro-1H-indol-3-ylidene)thiosemicarbazide

In the title compound, C15H19N5O3S, intramolecular N—H⋯O, N—H⋯N and C—H⋯S interactions occur and the three terminal C atoms of the hexyl group are disordered over two sites with an occupancy ratio of 0.664 (12):0.336 (12). In the crystal, inversion dimers linked by pairs of N—H⋯O hydrogen bonds occur and C—H⋯O bonds link the dimers into chains. A short C=O⋯π contact is also present.

In the title compound, C 15 H 19 N 5 O 3 S, intramolecular N-HÁ Á ÁO, N-HÁ Á ÁN and C-HÁ Á ÁS interactions occur and the three terminal C atoms of the hexyl group are disordered over two sites with an occupancy ratio of 0.664 (12):0.336 (12). In the crystal, inversion dimers linked by pairs of N-HÁ Á ÁO hydrogen bonds occur and C-HÁ Á ÁO bonds link the dimers into chains. A short C OÁ Á Á contact is also present.
Amongst these, isatins-derived thiosemicarbazones have gained a great deal of attention (Beauchard et al., 2006;Quenelle et al., 2006;Karali et al., 2007). Very recently, a number of N(4)-arylsubstituted isatin-3-thiosemicarbazones have been synthesized and reported as potent urease (a nickel-dependent metallo-enzyme) inhibitors (Pervez et al., 2008;Pervez et al., 2009). In continuation to the development of potent and non-or less toxic urease inhibitors, we report herein the crystal structure and preparation of the title compound (I, Fig. 1).
The molecules of the title compound consist of dimers owing to N-H···O type of intermolecular H-bondings forming R 2 2 (8) ring motifs (Bernstein et al., 1995). The molecules are interlinked in the form of polymeric chains due to C-H···O type of intermolecular H-bondings (Table 1, Fig. 2). There exist two S(5) and a S(6), R 2 2 (10) and R 3 3 (12) or R 2 2 (13) ring motifs as well (Fig. 2). In the title compound the group (C1-C9/N1-N5/O-O3) of the isatin moiety along with nitro substitution is planar with maximum r.m.s. deviation of 0.0348 Å from the mean square plane and the sulphur atom S1 is at a distance of -0.3497 (16) Å from this mean square plane. The terminating three carbons of the hexyl group are disordered over two sites with occupancy ratio of 0.664 (12):0.336 (12). The C==O···π and N-O···π interactions (Table 1), may also be responsible for stabilizing of the molecules.

Experimental
A solution of N 4 -hexylthiosemicarbazide (0.44 g, 2.5 mmol) in ethanol (10 ml) was added to a hot solution of 5-nitroisatin (0.48 g, 2.5 mmol) in 50% aqueous ethanol (30 ml) containing a few drops of glacial acetic acid. The reaction mixture was then heated under reflux for 2 h. The yellow crystalline solid formed during heating was collected by suction filtration.
Thorough washing with hot aqueous ethanol gave the title compound (I) in pure form (0.72 g, 82%), m.p. 513 K. The single crystals of (I) were grown in ethanol-n-hexane (1:4) system by diffusion method at room temperature.

Refinement
The H-atoms were positioned geometrically with N-H = 0.86, C-H = 0.93, 0.96 and 0.97 Å for aryl, methyl and methylene H atoms respectively and constrained to ride on their parent atoms, with U iso (H) = xU eq (C, N), where x = 1.5 for methyl and 1.2 for all other H atoms. Fig. 1. View of (I) with the atom numbering scheme. The thermal ellipsoids are drawn at the 30% probability level. H-atoms are shown by small circles of arbitrary radii. The single dotted lines represent the intramolecular H-bondings and the atoms of low occupancy factor are joined by double dotted lines.

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 Rfactors(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.