The crystal structure of methixene hydrochloride monohydrate

Abstract

The crystal structure of methixene hydrochloride monohydrate, 9-(N-methyl-3-piperidylmethyl)thioxanthene hydrochloride monohydrate, C20H2sNS. HCI.H20, has been determined by the heavy-atom method and refined three-dimensionally by the anisotropic least-squares method to give a final R value of 0068 for 2228 reflections. The space group is P21/a with Z=4, and the unit-cell dimensions are a = 15-320 + 0.003, b = 9 118 + 0.002, c = 13862 _+ 0.004 A, and fl = 94.75 + 0.02 °. All the hydrogen atoms were located on difference-Fourier syntheses, but their parameters were not refined. The crystal contains both enantiomorphs in an equal amount. The benzenoid rings are normal, and the best planes of the benzene rings make a dihedral angle of 1379 °. The meso atoms, C(9) and S, are significantly displaced from the benzene ring. The piperidyl ring is in a chair conformation. The piperidylmethyl group is 'boat axial' with respect to the central thioxanthene ring, and both the thioxanthen-9-ylmethyl and N-methyl groups are in an 'equatorial' position with respect to the piperidyl ring. All interatomic distances and angles are normal. The sulfur-carbon bond distance is 1-765 + 0.003/~. The average carboncarbon bond distance is 1.524 + 0.006/~ for carbon-carbon single bonds, 1.384 + 0.006 A, for carboncarbon bonds in the benzenoid ring, and 1.505 + 0.005 A, for carbon-carbon bonds involving C(9) and the benzenoid ring. The mean value of the nitrogen-carbon bond distance is 1488 + 0.006 A,. Each chloride ion is associated with three hydrogen bonds; one links to a quaternary ammonium ion and the other two link to two different water molecules. The packing of the molecules in the crystal is determined by the hydrogen bonding and van der Waals interactions.