5-Amino-6-methylquinolin-1-ium hydrogen malonate–malonic acid (2/1)

The asymmetric unit of the title compound, 2C10H11N2 +·2C3H3O4 −·C3H4O4, consists of one 5-amino-6-methylquinolin-1-ium cation, one hydrogen malonate (2-carboxyacetate) anion and one-half molecule of malonic acid which lies on a twofold rotation axis. The quinoline ring system is essentially planar, with a maximum deviation of 0.062 (2) Å for all non-H atoms. In the anion, an intramolecular O—H⋯O hydrogen bond generates an S(6) ring. In the crystal, the components are linked via N—H⋯O and O—H⋯O hydrogen bonds into layers parallel to the ac plane. The crystal structure also features weak C—H⋯O hydrogen bonds and a π–π stacking interaction with a centroid–centroid distance of 3.8189 (10) Å.

The asymmetric unit of the title compound, 2C 10 H 11 N 2 + Á-2C 3 H 3 O 4 À ÁC 3 H 4 O 4 , consists of one 5-amino-6-methylquinolin-1-ium cation, one hydrogen malonate (2-carboxyacetate) anion and one-half molecule of malonic acid which lies on a twofold rotation axis. The quinoline ring system is essentially planar, with a maximum deviation of 0.062 (2) Å for all non-H atoms. In the anion, an intramolecular O-HÁ Á ÁO hydrogen bond generates an S(6) ring. In the crystal, the components are linked via N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds into layers parallel to the ac plane. The crystal structure also features weak C-HÁ Á ÁO hydrogen bonds and astacking interaction with a centroid-centroid distance of 3.8189 (10) Å .

Kaliyaperumal Thanigaimani, Nuridayanti Che Khalib, Suhana Arshad and Ibrahim Abdul Razak Comment
Recently, hydrogen-bonding patterns involving quinoline and its derivatives with organic acid have been investigated (Thanigaimani et al., 2013a,b;Loh et al., 2010). Syntheses of the quinoline derivatives were discussed earlier (Sasaki et al., 1998;Reux et al., 2009). Quinolines and their derivatives are very important compounds because of their wide occurrence in natural products (Morimoto et al., 1991) and biologically active compounds (Markees et al., 1970). Herein we report the crystal structure and supramolecular patterns of the new compound containing quinoline derivative and malonic acid components.
The asymmetric unit of the title compound ( Fig. 1) contains a protonated 5-amino-6-methylquinolin-1-ium cation, a hydrogen malonate anion and a half of the malonic acid molecule. The dihedral angles between the quinoline ring and the planes formed by the malonate and malonic acid molecule are 10.39 (5) and 27.08 (8)°, respectively. The planar malonic acid molecule is located on a two-fold rotation axis. In the malonic acid, the C14-O5 bond distance of 1.1973 (19) Å is much shorter than the C14-O6 bond distance of 1.312 (2) Å indicating that the carboxyl group is not deprotonated in the crystal structure. The 5-amino-6-methylquinolinium cation is essentially planar with a maximum deviation of 0.062 (2) Å for atom C10. In the cation, a wider than normal angle [C1-N1-C9 = 123.32 (13)°] is subtended at the protonated N1 atom. The bond lengths (Allen et al., 1987) and angles are normal. The anion is stabilized by an intramolecular O2-H1O2···O4 hydrogen bond, which forms an S(6) ring motif (Bernstein et al., 1995).

Experimental
Hot methanol solutions (20 ml) of 5-amino-6-methylquinoline (39 mg, Aldrich) and malonic acid (26 mg, Aldrich) were mixed and warmed over a heating magnetic stirrer hotplate for a few minutes. The resulting solution was allowed to cool slowly at room temperature and crystals of the title compound (I) appeared after a few days.

Figure 1
The molecular structure of the title compound with atom labels with 50% probability displacement ellipsoids.  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.