Crystal structure of 9-(dibromomethyl)-1,1-difluoro-3,7-dimethyl-1H-[1,3,5,2]oxadiazaborinino[3,4-a][1,8]naphthyridin-11-ium-1-uide

The molecule in the title compound, C12H10BBr2F2N3O, exhibits point group symmetry m.


Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The 1,8-naphthyridine ring system is fused with a mixed difluororoxadiazaborinino unit. The entire oxadiazaborininonaphthyridine ring system is planar due to its location on a mirror plane running parallel to the ring system. In addition, the C atoms of the two methyl groups (C8 and C1) as well as the C atom (C12) of the dibromomethyl group are located on the mirror plane, hence only two pairs of the methyl H atoms, the two Br atoms and the two F atoms are above and below this plane. The F1-B1-F1 i and Br1 i -C12-Br1 angles [symmetry code: (i) x, Ày + 1 2 , z] are 113.6 (7) and 110.3 (3) , and the distances of the Br and F atoms to the plane are 1.5916 (6) and 1.141 (3) Å , respectively. The individual F-B bond length is 1.364 (5) Å and the Br-C bond length 1.940 (4) Å . Compared with the molecular structure of a related compound (Wu et al., 2012), the difference between the F1-B1-F1 i angles is 2.16 , while the bond lengths and angles in the oxadiazaborine ring moiety of the two structures are almost the same.

Figure 2
A view along the a axis of the crystal packing of the title compound. Hydrogen bonds are shown as dashed lines. Table 1 Hydrogen-bond geometry (Å , ).

Figure 3
A view along the b axis of the crystal packing of the title compound.

Synthesis and crystallization
BF 3 ÁOEt 2 (2 ml, 16 mmol) was added dropwise to an icecooled solution of 2,6-lutidine (1 ml) and N-[7-(dibromomethyl)-5-methyl-1,8-naphthyridin-2-yl]acetamide (0.37 g, 1 mmol) in anhydrous CH 2 Cl 2 (80 ml) under a nitrogen atmosphere. After the mixture had been stirred for 24 h under ambient temperature, the reaction was quenched with 20 ml distilled water. The aqueous layer was extracted with CH 2 Cl 2 (3 Â 50 ml); the organic layer was dried with anhydrous Na 2 SO 4 and the solvent removed under reduced pressure. The residue was purified by silica gel chromatography using CH 2 Cl 2 as eluent to give the pure product as a bright white powder (yield 0.19 g, 45%). Yellow crystals of the title compound were obtained from its CH 2 Cl 2 solution by slow evaporation at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were placed in calculated positions and included in the final cycles of refinement using a riding-model approximation with C-H = 0.96 Å and with U iso (H) = 1.2U eq (C) for aromatic and U iso (H) = 1.5U eq (C) for methyl H atoms.  Extinction correction: SHELXL, Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0042 (6) 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.