2,3-Diaminopyridinium 4-carboxybutanoate

In the title molecular salt, C5H8N3 +·C5H7O4 −, the 2,3-diaminopyridine molecule is protonated at the pyridine N atom. The cation is essentially planar, with a maximum deviation of 0.015 (2) Å, and the anion adopts an extended conformation. In the crystal, the hydrogen glutarate (4-carboxybutanoate) anions are self-assembled through O—H⋯O hydrogen bonds, forming chains. The cations are connected to the anion chains via N—H⋯O hydrogen bonds, forming a three-dimensional network. The crystal structure also features aromatic π–π interactions between the pyridinium cations, with a centroid–centroid distance of 3.4464 (10) Å.

In the title molecular salt, C 5 H 8 N 3 + ÁC 5 H 7 O 4 À , the 2,3diaminopyridine molecule is protonated at the pyridine N atom. The cation is essentially planar, with a maximum deviation of 0.015 (2) Å , and the anion adopts an extended conformation. In the crystal, the hydrogen glutarate (4carboxybutanoate) anions are self-assembled through O-HÁ Á ÁO hydrogen bonds, forming chains. The cations are connected to the anion chains via N-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network. The crystal structure also features aromaticinteractions between the pyridinium cations, with a centroid-centroid distance of 3.4464 (10) Å .
Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 (Bis et al., 2006;Gellert & Hsu, 1988). Glutaric acid is found in the blood and urine. It is used in the synthesis of pharmaceuticals, surfactants and metal finishing compounds. Herein, we report the crystal structure determination of the title compound, (I).
The asymmetric unit (Fig. 1) contains a 2,3-diaminopyridinium cation and hydrogenglutarate anion. The cation is essentially planar, with a maximum deviation of 0.015 (2) Å for atom C1. In the 2,3-diaminopyridinium cation, a wide angle [123.94 (14)°] is subtended at the protonated N1 atom. The conformation of the hydrogenglutarate anion can be described by the two torsion angles C6-C7-C8-C9 of 58.61 (16)° and C7-C8-C9-C10 of 175.91 (13)°. As evident from the torsion angles, the hydrogenglutarate anion is in a fully extended conformation (Saraswathi et al., 2001). Of the two carboxyl groups, one is deprotonated while the other is not. The bond lengths (Allen et al., 1987) and angles are within normal ranges.

Experimental
Hot methanol solution (20 ml) of 2,3-diaminopyridine (52 mg, Aldrich) and glutaric acid (66 mg, Merck) 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 brown plates of the title compound appeared after a few days.

Refinement
The C-bonded hydrogen atoms were located from a difference Fourier maps and refined freely [C-H = 0.96 (2)-1.00 (2) Å] and C-H = 0.93 (2)-1.01 (2) Å]. The O-and N-bonded hydrogen atoms can also be located but in the final refinement, 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 > 2σ(F 2 ) is used only for calculating Rfactors(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.