3-Carboxy-2-(2-cyclopropylamino-4-methylpyridinium-3-ylamino)pyridinium dinitrate dihydrate

The two benzene rings in the cation of the title compound, C15H18N4O2 2+·2NO3 −·2H2O, are almost perpendicular [dihedral angle = 91.6 (2)°]. In the crystal, the components are linked by O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds.


Comment
Intermolecular interactions are responsible for crystal packing and gaining an understanding of them allows us to comprehend collective properties and permits the design of new crystals with specific physical and chemical properties (Lam & Mak, 2000). Hydrogen bonding is one of the most important noncovalent interactions that determines and controls the assembly of molecules and ions (Desiraju, 2002, Liu et al., 2008, Biswas et al., 2009. Organic salts based on hydrogen bonding are also a research field receiving great attention in recent years. As an extension of our study concentrating on hydrogen bonded assembly of organic acid and organic base (Jin et al., 2010), herein we report the crystal structure of 2-(2-(cyclopropylamino)-4-methylpyridinium-3-ylamino) nicotinic acid dinitrate dihydrate.
The asymmetric unit of the compound consists of one dication, two nitrate anions, and two free water molecules ( Fig.   1), respectively.
The compound is an organic salt. At every cation there are bound two nitrate anions through the N-H···O hydrogen bond.
And the two water molecules were connected with carbonyl and OH of the carboxyl group of the cation rspectively via the O-H···O hydrogen bond. Under these interactions the cation, the anions, and the water molecules form a pentacomponent adduct. Such kind of adducts were connected together by the N-H···O, O-H···O, O-pi, and CH 2 -O interactions to form a one-dimensional chain running along the a axis direction. Two such chains were joined together via the CH-O, and CH 2 -O interactions to form double chain structure (Fig. 2). The double chains were linked together via the water molecule that is bound with the carboxyl group to form two-dimensional sheet extending along the ac plane. The two-dimensional sheets further stacked along the b axis direction through the nitrate group to form three-dimensional layer network structure.

Experimental
A solution of 2-(2-(cyclopropylamino)-4-methylpyridin-3-ylamino) nicotinic acid (28.4 mg, 0.1 mmol) was dissolved in 5 ml of water and 1 ml of conc. HNO 3 under continuous stirring. The solution was stirred for about 1 h at room temperature, then the solution was filtered into a test tube. The solution was left standing at room temperature for several days, colorless block crystals were isolated after slow evaporation of the solution in air at ambient temperature. The crystals were collected and dried in air to give the title compound.