Morphine hydrochloride anhydrate1

In the title molecular salt [systematic name: (5α,6α)-7,8-didehydro-4,5-epoxy-17-methylmorphinan-3,6-diol hydrochloride], C17H20NO3 +·Cl−, the conformation of the morphinium ion is in agreement with the characteristics of the previously reported morphine forms [for example, Gylbert (1973 ▶). Acta Cryst. B29, 1630–1635]. In the crystal, the cations and chloride anions are linked into a helical chain propagating parallel to the b-axis direction by N—H⋯Cl and O—H⋯Cl hydrogen bonds. The title salt and the morphine monohydrate [Bye (1976 ▶) Acta Chem. Scand. 30, 549–554] display very similar one-dimensional packing modes of their morphine components.

The asymmetric unit of the title salt contains of one formula unit ( Figure 1). The geometry of the molecular morphine scaffold with its five rings agrees with the characteristics of the previously investigated salt and free base structures. The morphinium cation of the title salt is doubly O-H···Cl bonded to the anion so that a R 1 2 (10) ring (Etter et al., 1990;Bernstein et al., 1995) is formed. The Clion is additionally N-H···Cl bonded to the protonation site of a second cation, which is related to the first cation by a 2 1 screw operation parallel to the b-axis. An infinite hydrogen-bonded chain is formed as a result of these interactions, and the chain structure propagates parallel to the b-axis ( Figure 2a). The closest intermolecular C-H···O and C-H···π contacts are listed in Table 2 and shown in Figure 2 b.
The program XPac (Gelbrich & Hursthouse, 2005) was used to compare the packing of the morphinium ions with that of the analogous moieties in the five related structures mentioned above (Bye, 1976;Gylbert, 1973;Mackay & Hodgkin, 1955;Lutz & Spek, 1998;Wongweichintana et al., 1984). In this group, the closest similarity relationship involving the title structure is based on a single stack of molecules ('one-dimensional supramolecular construct′, Figure 3) that is also present in the monohydrate (Bye, 1976). In both crystals the corresponding stacking vector lies parallel [100] with d = 7.359 Å for the title structure and d = 7.438 Å for the monohydrate. The corresponding XPac dissimilarity index x (Gelbrich et al., 2012) is 8.2, calculated for a cluster comprising a central molecule and its two next neighbours in the stack on the basis of the positions of all 21 non-H atoms. This value confirms that the fundamental geometry of the stack is maintained. However, the geometry of the stack is somewhat affected by its crystal environment, which accomodates the specific hydrogen bond preferences of the second chemical component, i.e. Clin the case of the title structure and H 2 O in the monohydrate.

Experimental
The investigated compound was obtained from Heilmittelwerke Wien, Austria. Block-shaped crystals of the title compound were produced by slow evaporation from an ethanol solution.

Refinement
The H atoms were identified in a difference map. Methyl H atoms were idealized and included as rigid groups allowed to  (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2010).

Figure 1
Asymmetric unit of the title compound. Displacement ellipsoids are drawn at the 50% probability level, with hydrogen atoms shown as spheres of arbitrary size.   Common one-dimensional supramolecular construct (SC) of the title structure and the morphine monohydrate (Bye, 1976  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.