Crystal structures of the dioxane hemisolvates of N-(7-bromomethyl-1,8-naphthyridin-2-yl)acetamide and bis[N-(7-dibromomethyl-1,8-naphthyridin-2-yl)acetamide]

The syntheses and crystal structures of the title dioxane hemisolvates of N-(7-bromomethyl-1,8-naphthyridin-2-yl)acetamide and bis[N-(7-dibromomethyl-1,8-naphthyridin-2-yl)acetamide] are described.


Structural commentary
The molecular structures of the title compounds, (I) and (II), are illustrated in Figs. 1 and 2, respectively. The asymmetric unit of compound (I) consists of one molecule of the naphthyridine derivative and one half of a 1,4-dioxane solvent molecule, with the whole molecule being generated by inversion symmetry. The naphthyridine ring of the host molecule is essentially planar [maximum deviations from the mean plane being 0.034 (3) Å for N1 and À0.034 (3) Å for C6]. The plane defined by the acetamido group is inclined at an angle of 18.9 (2) with respect to the mean plane of the 1,8-naphthyr- ISSN 2056-9890 idine moiety. The torsion angle along the atomic sequence N2-C1-C9-Br1 is 83.6 (4) . The dioxane molecule is connected to the host molecule via C-HÁ Á ÁO hydrogen bonding (Table 1 and Fig. 1).
The asymmetric unit of the inclusion compound (II) contains two crystallographically independent, but conformationally similar molecules of the 1,8-naphthyridine derivative and one half molecule of a positionally disordered 1,4dioxane, the whole molecule of the latter is generated by inversion symmetry and is disordered over two positions [occupancy ratio = 0.890 (5):0110 (5)]. The structural features of the host molecule in (II) resemble those found in the reported structure of N-(7-dibromomethyl-5-methyl-1,8naphthyridin-2-yl)acetamide (Gou et al., 2013). The dihedral angles between the mean planes of the naphthyridine moiety and the acetylamido group are 27.6 (1) and 20.4 (1) , respectively. The dibromomethyl group is oriented in such a way that the two Br atoms are tilted away from the plane of the respective naphthyridine moiety. The dioxane molecule is connected to the host molecule via C-HÁ Á ÁO hydrogen bonding (Table 2 and Fig. 2).

Supramolecular features
In the crystal of compound (I), 1:1 host-guest units related by the 2 1 screw axis are linked via hydrogen bonding to form infinite supramolecular strands ( Fig. 3 and Table 1). In this molecular arrangement, the amino H atom and atom N2 participate in intermolecular N-HÁ Á ÁN hydrogen bonding, whereas atom N1 is involved in the formation of a weaker C-HÁ Á ÁN interaction with one of the methylene H atoms of a symmetry-related molecule acting as a donor.  Table 1 Hydrogen-and halogen-bond geometry (Å , ) for (I).

Figure 1
A view of the molecular structure of compound (I), showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Dashed lines represent halogen bonds (Table 1).

Figure 2
A view of the two independent molecules of compound (II), showing the atom labelling and ring specification. Displacement ellipsoids are drawn at the 50% probability level. For the sake of clarity, the minor-disordered component of the dioxane molecule has been omitted. Dashed lines represent hydrogen bonds (Table 2).
According to the observed stoichiometric ratio of the crystal components in (II), the host molecules contribute in a different way in noncovalent intermolecular bonding. The crystal structure is constructed of 2:1 host-guest complexes ( Fig. 2 and Table 2), in which the independent host molecules form a strongly distorted dimer held together by two N-HÁ Á ÁN hydrogen bonds and two weak C methyl -HÁ Á ÁN contacts. One of the arene H atoms of this dimeric unit acts as a donor for C-HÁ Á ÁO hydrogen bonding to the guest molecule. As is shown in Fig. 4 and Table 2, the Br atoms of only one host molecule participate in intermolecular interactions.
N-(7-Bromomethyl- Crystals of (I) and (II) suitable for X-ray analysis were obtained by slow evaporation of the solvent (1,4-dioxane) from solutions of the respective compounds.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. In both compounds, the N-H H atoms were located from difference Fourier maps and refined freely. C-bound H atoms were placed geometrically and allowed to ride on their attached C atoms, with C-H distances of 0.95-1.00 Å and U iso (H) = 1.5U eq (C-methyl), or 1.2U eq (C) for other H atoms.  Computer programs: APEX2 (Bruker, 2014), SAINT (Bruker, 2014), SHELXS97 (Sheldrick, 2008), SHELXL2013 (Sheldrick, 2015), ORTEP-3 for Windows (Farrugia, 2012) and SHELXTL (Sheldrick, 2008 For both structures, data collection: APEX2 (Bruker, 2014); cell refinement: SAINT (Bruker, 2014); data reduction: SAINT (Bruker, 2014); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).  Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.