Crystal structure analysis of the biologically active drug mol­ecule riluzole and riluzolium chloride

This study is an investigation into the crystal structure of the biologically active drug mol­ecule riluzole [RZ, 6-(tri­fluoro­meth­oxy)-1,3-benzo­thia­zol-2-amine], C8H5F3N2OS, and its derivative, the riluzolium chloride salt [RZHCl, 2-amino-6-(tri­fluoro­meth­oxy)-1,3-benzo­thia­zol-3-ium chloride], C8H6F3N2OS+·Cl−. In spite of repeated efforts to crystallize the drug, its crystal structure has not been reported to date, hence the current study provides a method for obtaining crystals of both riluzole and its corresponding salt, riluzolium hydro­chloride. The salt was obtained by grinding HCl with the drug and crystallizing the obtained solid from di­chloro­methane. The crystals of riluzole were obtained in the presence of L-glutamic acid and D-glutamic acid in separate experiments. In the crystal structure of RZHCl, the –OCF3 moiety is perpendicular to the mol­ecular plane containing the riluzolium ion, as can be seen by the torsion angle of 107.4 (3)°. In the case of riluzole, the torsion angles of the four different mol­ecules in the asymmetric unit show that in three cases the tri­fluoro­meth­oxy group is perpendicular to the riluzole mol­ecular plane and only in one mol­ecule does the –OCF3 group lie in the same mol­ecular plane. The crystal structure of riluzole primarily consists of strong N—H⋯N hydrogen bonds along with weak C—H⋯F, C—H⋯S, F⋯F, C⋯C and C⋯S inter­actions, while that of its salt is stabilized by strong [N—H]+⋯Cl− and weak C—H⋯Cl−, N—H⋯S, C—H⋯F, C⋯C, S⋯N and S⋯Cl− inter­actions.