3-{[6-(4-Chlorophenyl)imidazo[2,1-b][1,3,4]thiadiazol-2-yl]methyl}-1,2-benzoxazole

In the title compound, C18H11ClN4OS, the benzisoxazole and imidazothiadiazole rings are inclined at an angle of 23.81 (7)° with respect to each other. The imidazothiadiazole and chlorophenyl rings make a dihedral angle of 27.34 (3)°. In the crystal, intermolecular C—H⋯N interactions generate a chain along the c axis and C—H⋯O interactions form centrosymmetric dimers resulting in an R 2 2(26) graph-set motif. Moreover, the C—H⋯N and S⋯N [3.206 (4) Å] interactions links the molecules into R(7) ring motifs. The packing is further stabilized by π–π stacking interactions between the thiadiazole rings with a shortest centroid–centroid distance of 3.497 (3) Å. In addition, C—H⋯π interactions are observed in the crystal structure

In the title compound, C 18 H 11 ClN 4 OS, the benzisoxazole and imidazothiadiazole rings are inclined at an angle of 23.81 (7) with respect to each other. The imidazothiadiazole and chlorophenyl rings make a dihedral angle of 27.34 (3) . In the crystal, intermolecular C-HÁ Á ÁN interactions generate a chain along the c axis and C-HÁ Á ÁO interactions form centrosymmetric dimers resulting in an R 2 2 (26) graph-set motif. Moreover, the C-HÁ Á ÁN and SÁ Á ÁN [3.206 (4) Å ] interactions links the molecules into R(7) ring motifs. The packing is further stabilized bystacking interactions between the thiadiazole rings with a shortest centroid-centroid distance of 3.497 (3) Å . In addition, C-HÁ Á Á interactions are observed in the crystal structure
NSB is thankful to the University Grants Commission (UGC), India, for financial assistance and the Department of Science and Technology, (DST), India, for the data-collection facility under the IRHPA-DST program.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: GW2098).  (Priya et al., 2005) and are useful in different therapies. Amongst them, five membered heterocyclic ring 1,3,4-thiadiazoles find wide application in designing compounds possessing useful properties (Katritzky et al., 1984;Diamond & Sevrain, 2003a,b;Nakao et al., 2002a,b). Due to the increasing importance of these heterocycles in biological and pharmaceutical fields, new chemical entities were synthesized by incorporating active pharmacophores in a single molecular frame work so as to enhance their biological activities.In the title compound, the benzisoxazole (O1/N4/ C3/C13-18) and imidazothiadiazole (S1/N1-N3/C1/C4-C6) rings are individually planar similar to those reported earlier (Sun & Zhang, 2009) with maximum deviations of 0.038 (3)Å for C1 and 0.016 (3)Å for C3 respectively. The mean planes of the benzisoxazole and imidazothiadiazole are inclined at an angle 23.81 (7)° with each other. The imidazothiadiazole and chlorophenyl rings make a dihedral angle of 27.34 (3)°. The thiadiazole moiety displays differences in the bond lengths between S1-C1/S1-C4 [1.756 (3)/1.736 (3)]. This can be attributed to the resonance effects of the imidazole ring which is stronger than that due to thiadiazole group. The crystal structure is stabilized by intermolecular C-H···N, C-H···O and S···N interactions. The C-H···N interaction generates chain like pattern along c axis. The C-H···O interaction forms centrosymmetric head-to-head dimers about inversion centers corresponding to R22(26) graph set motif (Bernstein et al., 1995). The C-H···N interaction along with S···N [3.206 (4) Å]interaction results in a ring motif with a graph set R(7). The molecular packing is further stabilized by π-π stacking interactions between thiadiazole rings (Cg3: centroid of S1/C1/N2/ N3/C4) with the shortest centroid-centroid distance 3.497 (3) Å. In addition, π-ring interactions of the type C-H···Cg (Cg being the centroids of rings C7-C12 and C13-C18) are also observed in the crystal structure; details have been given in Table 1.

Experimental
The title compound was synthesized by following the procedure reported earlier (Lamani et al., 2009).

Refinement
The H atoms were placed at calculated positions in the riding model approximation with aromatic C-H = 0.93Å and methylene C-H = 0.97 Å, and U iso (H) = 1.2U eq (N/C). Fig. 1. ORTEP (Farrugia, 1997)

Special details
Experimental. The compound was synthesized by following the procedure given in Lamani et al., (2009) 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.