Cilansetron hydro­chloride monohydrate, modification A (monoclinic)

The absolute configuration of the monoclinic form of the title compound, (−)‐5,6,9,10‐tetra­hydro‐10‐[(2‐methyl‐1H‐imid­a­zol‐1‐yl)­methyl]‐4H‐pyrido­[3,2,1‐jk]­carbazol‐11(8H)‐one mono­hydro­chloride monohydrate, C20H22N3O+·Cl−·H2O, was established as R at the asymmetric carbon adjacent to the carbonyl function. This form [cf. the orthorhombic form; Jones et al. (2003). Acta Cryst. E59, o41–o43] involves two independent formula units with different ring conformations of the six‐membered N‐heterocycle, and somewhat different orientations of the imidazole ring. Each independent formula unit forms a helical hydrogen‐bonded chain of alternating water and chloride residues; the cations are hydrogen bonded laterally to the chlorides.