Monoclinic form I of clopidogrel hydrogen sulfate from powder diffraction data.

The asymmetric unit of the title compound, C(16)H(17)ClNO(2)S(+)·HSO(4) (-), (I) [systematic name: (+)-(S)-5-[(2-chloro-phen-yl)(meth-oxy-carbon-yl)meth-yl]-4,5,6,7-tetra-hydro-thieno[3,2-c]pyridin-5-ium hydrogen sulfate], contains two independent cations of clopidogrel and two independent hydrogensulfate anions. The two independent cations are of similar conformation; however, this differs from that observed in ortho-rhom-bic form (II) [Bousquet et al. (2003 ▶). US Patent No. 6 504 030]. The H-N-C(chiral)-H fragment shows a trans conformation in both independent cations in (I) and a gauche conformation in (II). In (I), classical inter-molecular N-H⋯O and O-H⋯O hydrogen bonds link two independent cations and two independent anions into an isolated cluster, in which two cations inter-act with one anion only via N-H⋯O hydrogen bonds. Weak inter-molecular C-H⋯O hydrogen bonds further consolidate the crystal packing.