5-Chloro-N-(4,5-dihydro-1H-imidazol-2-yl)-2,1,3-benzothiadiazol-4-amine (tizanidine)

There are two independent molecules (A and B) with similar conformations in the asymmetric unit of the title compound, C9H8ClN5S. The benzothiadiazole ring systems of both molecules are essentially planar [maximum deviation = 0.021 (2) A in molecule A and 0.022 (1) A in molecule B] and make dihedral angles of 68.78 (9) and 54.39 (8)degrees, respectively, with the mean planes of their 4,5-dihydro-1H-imidazole rings. An intramolecular N-H...Cl hydrogen bond occurs in molecule B. In the crystal, both molecules form centrosymmetric dimers through pi-stacking of their benzothiadiazole rings, with interplanar distances of 3.3174 (7) and 3.2943 (6) A. These dimers are further linked via pairs of N-H...N hydrogen bonds with the dihydroimidazole rings as the hydrogen-bonding donors and one of the benzothiadiazole N atoms as the acceptors, generating R (2) 2(16) ring motifs. The A (2) and B (2) dimers in turn form additional N-H...N hydrogen bonds with the secondary amine as the H-atom donor and the dihydroimidazole N atom as the acceptor. These R (2) 2(8)-type interactions connect the A (2) and B (2) dimers with each other, forming infinite chains along [1 <file type="gif" name="AYE_zl2351_mu1.gif"/> 1].