Crystal structure of 2-aminopyridinium 6-chloronicotinate

In the title salt, C5H7N+·C6H3ClNO−, the 2-aminopyridinium cation interacts with the carboxylate group of the 6-chloronicotinate anion through a pair of independent N—H⋯O hydrogen bonds, forming an R 2 2(8) ring motif. In the crystal, these dimeric units are connected further via N—H⋯O hydrogen bonds, forming chains along [001]. In addition, weak C—H⋯N and C—H⋯O hydrogen bonds, together with weak π–π interactions, with centroid–centroid distances of 3.6560 (5) and 3.6295 (5) Å, connect the chains, forming a two-dimensional network parallel to (100).

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009) and Mercury (Macrae et al., 2008); software used to prepare material for publication: PLATON. Noncovalent interactions such as hydrogen bonding, anion-π, cation-π, and π-π interactions, and other weak forces play a central role in many areas. They are very important in deciding the conformation of molecules, chemical reactions, molecular recognition, regulating biochemical processes and governing the organization of multicomponent supramolecular assemblies (García-Raso et al., 2009). 2-Aminopyridines are used in the manufacture of pharmaceutical drugs, especially for the treatment of neurological ailments (Schwid et al., 1997). Pyridine heterocycles and their derivatives have large applications in the field of photo-chemical, electrochemical and catalytic process. Some pyridine derivatives possess non-linear optical (NLO) properties (Rajkumar et al., 2015). The crystal structure of 2-aminopyridinium isonicotinate 2-aminopyridine has already been reported (Xie, 2007). The salts of aminopyridine-thiophenecarboxylic acid (Jennifer & Muthiah, 2014) have been recently reported from our laboratory. We report herein the crystal structure of the title molecular salt, obtained by the reaction of 2-aminopyridine with 6-chloronicotinic acid.

S2. Experimental
A hot ethanolic solution of 2-aminopyridine (23 mg, Aldrich) and 6-chloronicotinic acid (39 mg, Alfa Aesar) was warmed for half an hour over a water bath. The mixture was cooled slowly and kept at room temperature. After a few days colourless plate like crystals were obtained.

S3. Refinement
Hydrogen atoms boned to C atoms were place in calculated postions with with C-H = 0.95Å and included with U iso (H) = 1.2U eq (C). H atoms boned to N atoms were refined independently with isotropic displacement parameters.

Figure 1
The asymmetric unit of the title compound, showing 30% probability displacement ellipsoids.

Figure 2
Part of the crystal structure with hydrogen bonds shown as dashed lines. Hydrogen atoms not involved hydrogen bonding have been removed for clarity. where P = (FO 2 + 2FC 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.50 e Å −3 Δρ min = −0.22 e Å −3 Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.