N-(7-Dibromomethyl-5-methyl-1,8-naphthyridin-2-yl)acetamide–pyrrolidine-2,5-dione (1/1)

In the title co-crystal, C12H11Br2N3O·C4H5NO2, the naphthyridine derivative and the pyrrolidine-2,5-dione molecules have crystallographic mirror-plane symmetry with all non-H atoms, except the Br atom, located on the mirror plane. In the crystal, N—H⋯N, N—H⋯O and C—H⋯O hydrogen bonds link the molecules into heterodimers. These dimers are further linked into a one-dimensional structure along [010] by weak C—Br⋯O interactions [Br⋯O = 3.028 (5) Å and C—Br⋯O = 158.52 (4)°].


Related literature
The structure of the title co-crystal is shown in Figs. 1 and 2 and hydrogen-bond geometry is given in Table 1. Both molecules are located on a mirror plane. There are three (N-H···N, N-H···O and C-H···O) intermoleular hydrogen bonds between the crystal components linking the molecules to form heterodimers. The complementarity of hydrogenbonding interactions stabilizes the dimeric structure, and, most probably, it is the reason why the two components were not easily separated during chromatographic procedure.
Experimental 7-Acetylamino-2,4-dimethyl-1,8-naphthyridine (Wang et al., 2008;Henry & Hammond, 1977) (500 mg, 2,32 mmol) and N-bromosuccinimide (0.49 g, 2.79 mmol) were added to an acetonitrile (20 ml) solution in the nitrogen atmosphere. The mixture was stirred at room temperature in the presence of light, a 250 W infrared lamp was used as a light source, for 4 hrs. Excess solvent was removed and the crude product was purified by column chromatography using dichloromethane/methanol (39:1) as the mobile phase to give a white powder. Yield: 250 mg (30%). Crystals suitable for X-ray

Refinement
All H atoms were placed in calculated positions. The H atoms were constrained to an ideal geometry with C-H distances of 0.93-0.96 Å, U iso (H) = 1.5U eq (C) for methyl H atoms and U iso (H) =1.2U eq (C) for the remaining H atoms, and N-H distance of 0.86 Å, U iso (H) = 1.2U eq (N). refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg,1999); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figure 1
The molecular structure of the title compound with atom labels and 30% probability displacement ellipsoids, and the disorders of hydrogen atoms are shown.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.