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, C(9)H(8)ClN(5)S. The benzothia­diazole ring systems of both mol­ecules are essentially planar [maximum deviation = 0.021 (2) Å in mol­ecule A and 0.022 (1) Å in mol­ecule B] and make dihedral angles of 68.78 (9) and 54.39 (8)°, 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 π-stacking of their benzothia­diazole rings, with inter­planar distances of 3.3174 (7) and 3.2943 (6) Å. 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[Image: see text]1].