1,3-Benzothiazole–oxalic acid (2/1)

The asymmetric unit of the title compound, C7H5NS·0.5C2H2O4, contains one benzothiazole molecule and half an oxalic acid molecule, the complete molecule being generated by inversion symmetry. The benzothiazole molecule is essentially planar, with a maximum deviation of 0.007 (1) Å. In the crystal, the benzothiazole molecules interact with the oxalic acid molecules via O—H⋯N and C—H⋯O hydrogen bonds generating R 2 2(8) (× 2) and R 4 4(10) motifs, thereby forming supramolecular ribbons along [101].

The asymmetric unit of the title compound, C 7 H 5 NSÁ-0.5C 2 H 2 O 4 , contains one benzothiazole molecule and half an oxalic acid molecule, the complete molecule being generated by inversion symmetry. The benzothiazole molecule is essentially planar, with a maximum deviation of 0.007 (1) Å . In the crystal, the benzothiazole molecules interact with the oxalic acid molecules via O-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds generating R 2 2 (8) (Â 2) and R 4 4 (10) motifs, thereby forming supramolecular ribbons along [101].

Comment
Benzothiazoles are used as anti-neoplastic agents and show anti-nociceptive, anti-inflammatory and anti-tumour activities (Bradshaw et al., 1998;Dögruer et al., 1998). Some Schiff bases derived from thiazole and benzothiazoles (Dash et al., 1980) and several derivatives of the styryl-benzothiazoles have also shown biological activity (Cox et al., 1982). In view of the above biological activities associated with the benzothiazole, herein, we present the title compound (I), extracted from the juice of Guava (Psidium guajava).
The asymmetric unit of the title compound, (I), contains one benzothiazole molecule and a half of an oxalic acid molecule (which lies on an inversion centre) as detailed in Fig. 1. The benzothiazole (N1/S1/C1-C7) molecule is essentially planar, with a maximum deviation of 0.007 (1) Å for atom C6.

Experimental
The juice of Guava (Psidium guajava) was extracted using soxhlet extraction method with methanol as solvent. After 24 hours at room temperature, a precipitate was formed and the filtrate removed. The precipitate was washed by using a mixture (90-100) ml of n-hexane-ethyl acetate. It was recrystallized by dissolving in methanol. Brown crystals were formed which melted at M.pt 323 K.

Refinement
Atom H1O2 was located from a difference Fourier map and refined with U iso (H) = 1.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.