Crystal structure of N-(7-dibromomethyl-5-methyl-1,8-naphthyridin-2-yl)benzamide–pyrrolidine-2,5-dione (1/1)

The title crystal is a co-crystal with the 1,8-naphthyridine derivative crystallizing with one molecule of succinimide per formula unit. In the crystal, the two molecules are mutually linked by N—H⋯O and N—H⋯N hydrogen bonds. The packing is consolidated by C—H⋯(O,N) hydrogen bonds and π–π stacking interactions.


Chemical context
1,8-Naphthyridine derivatives are important heterocyclic compounds that exhibit excellent biochemical and pharmacological properties. Moreover, these compounds benefit from conjugate -electronic structures and are widely used as ligands in the synthesis of metal complexes (Tang et al., 2015;Matveeva et al., 2012Matveeva et al., , 2013, functional materials (Kuo et al., 2011;Katz et al., 2007;Hu & Chen, 2010) or as catalysts (Fuentes et al., 2011;Yamazaki et al., 2011). In a number of studies, the fluorescent properties of naphthyridines have been investigated (Yu et al., 2013;Li et al., 2012), in particular as selective fluorescent chemosensors for small biological molecules through hydrogen bonding (Nakatani et al., 2013;Liang et al., 2012). 1,8-Naphthyridin-BF 2 complexes are known to be fluorescent dyes with high chemical stability , high fluorescence quantum yields (Quan et al., 2012), high extinction coefficients (Wu et al., 2013) and sharp fluorescence peaks (Du et al., 2014). Some antiviral medications are also based on 1,8-naphthyridines (Elansary et al., 2014). In this context we aimed to synthesize the title 1,8naphthyridine derivative and report here on the crystal structure of the obtained co-crystal with pyrrolidine-2,5-dione (succinimide).

Figure 2
The different types of hydrogen bonds between the two molecules and pairs of molecules; intramolecular hydrogen bonds are shown as blue dashed lines and intermolecular hydrogen bonds are shown as turquoise dashed lines.

Figure 3
A view along the c axis, showing the crystal packing of the title compound.

Database survey
In the Cambridge Structural Database (Version 5.37; Groom et al., 2016), the structural data for a very similar 1,8-naphthyridine derivative have been deposited (CSD refcode LESBOC; Gou et al., 2013). Instead of a benzamide, the latter is an acetamide where the dihedral angle between the naphthyridine moiety and the succinimide co-molecule is 14.1 .

Synthesis and crystallization
N-(5,7-dimethyl-1,8-naphthyridin-2-yl)benzamide (Wu et al., 2012) (0.277 g,1 mmol) and N-bromosuccinimide (0.356 g, 2 mmol) were added to an dry acetonitrile (30 ml) solution under nitrogen atmosphere. The mixture was refluxed at room temperature in the presence of light with a 250 W infrared lamp for 4 h. Excess solvent was removed and the crude product was purified by column chromatography using dichloromethane/methanol (120:1) as the mobile phase to give a light-yellow powder (yield: 0.1 g; 19%). Crystals suitable for X-ray analysis were obtained by slow diffusion of a dichloromethane solution at ambient temperature. Several cycles of purification by chromatography were used to reduce the amount of succinimide.

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. 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 > 2sigma(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.