7-(2,2-Dimethylpropanamido)-2-methyl-1,8-naphthyridin-1-ium chloride monohydrate

The asymmetric unit of the title compound, C14H18N3O+·Cl−·H2O, comprises a substituted amido–naphthyridine cation, a chloride anion and a water molecule of crystallization. Intramolecular C—H⋯O hydrogen bonds generate six-membered rings, producing an S(6) ring motif. The amido group is twisted from the naphthyridine ring, making a dihedral angle of 17.65 (7)°. The crystal structure is stabilized by intermolecular N—H⋯O, N—H⋯Cl, O—H⋯Cl (× 2), and C—H⋯O (× 2) hydrogen bonds. These interactions linked neighbouring molecules into chains along the a and b axes of the crystal, thus forming molecular sheets parallel to the (001) plane.

The asymmetric unit of the title compound, C 14 H 18 N 3 O + ÁCl À Á-H 2 O, comprises a substituted amido-naphthyridine cation, a chloride anion and a water molecule of crystallization. Intramolecular C-HÁ Á ÁO hydrogen bonds generate sixmembered rings, producing an S(6) ring motif. The amido group is twisted from the naphthyridine ring, making a dihedral angle of 17.65 (7) . The crystal structure is stabilized by intermolecular N-HÁ Á ÁO, N-HÁ Á ÁCl, O-HÁ Á ÁCl (Â 2), and C-HÁ Á ÁO (Â 2) hydrogen bonds. These interactions linked neighbouring molecules into chains along the a and b axes of the crystal, thus forming molecular sheets parallel to the (001) plane.

Comment
Naphthyridine or naphthyridone systems are of great importance due to their broad spectrum of biological activities. Substituted 1,8-naphthyridine compounds are used as antihypertensives, antiarrhythmics, herbicide safeners and also as immunostimulants (Goswami et al., 2005). Naphthyridine molecules also have interesting crystal structures (Carmen et al., 2004) and are used in molecular recognition chemistry (Goswami et al., 2005;Yu et al., 2008).
In the title compound (I), Fig. 1, intramolecular C-H···O hydrogen bond generates six-membered ring, producing S (6) ring motif (Bernstein et al., 1995). The chloride anion and water molecule are mediated to link neighbouring molecules together through hydrogen bonds. The amido group is twisted from the naphthyridine ring making a dihedral angle of 17.65 (7)°. The crystal structure is stabilized by intermolecular N-H···O, N-H···Cl, O-H···Cl(x 2), and C-H···O (x 2) hydrogen bonds. These interactions linked neighbouring molecules together as chains along the a and b axes of the crystal, thus forming 2-D molecular sheets parallel to the (001) plane.

Experimental
In a round bottom flask, 7-methyl-[1,8]naphthyridin-2-ylamine (100 mg, 0.63 mmol) and triethyl amine (0.1 mL) were stirred in dry dichloromethane (1 mL) under nitrogen at 0 ° C. Pivaloyl chloride (0.116 mL, 0.95 mmol) was then added dropwise. After 1 h, the solvent was removed and the residue was neutralized with saturated NaHCO 3 and fresh dichloromethane was added. The organic part was collected and removed under reduced pressure. The crude product was then purified by column chromatography using ethylacetate and petroleum ether (1:1) which offered the entitled compound as an off-white crystalline solid (82 mg, 53%), m.p. 66-68 ° C.

Refinement
Hydrogen atoms of the water molecule and N-bound H atoms were located from the difference Fourier map and refined freely, see Table 1. The rest of the hydrogen atoms were positioned geometrically and constrained to refine with the parent atoms with U iso (H) = 1.2 or 1.5 U eq (C). A rotating group model applied for the methyl group bound to the naphthyridine ring.

Special details
Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment.
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.