4-Aminopyridinium 5-carboxypentanoate monohydrate

In the title hydrated salt, C5H7N2 +·C6H9O4 −·H2O, the carboxy H atom is disordered over two positions with equal occupancy. In the crystal, O atoms of the 5-carboxypentanoate anion link the 4-aminopyridinium cations and water molecules into a three-dimensional network via N—H⋯O hydrogen bonds. The crystal structure is further consolidated by O—H⋯O hydrogen bonds involving the anion and the solvent water molecule.

In the title hydrated salt, C 5 H 7 N 2 + ÁC 6 H 9 O 4 À ÁH 2 O, the carboxy H atom is disordered over two positions with equal occupancy. In the crystal, O atoms of the 5-carboxypentanoate anion link the 4-aminopyridinium cations and water molecules into a three-dimensional network via N-HÁ Á ÁO hydrogen bonds. The crystal structure is further consolidated by O-HÁ Á ÁO hydrogen bonds involving the anion and the solvent water molecule.
The asymmetric unit of the title compound C 5 H 7 N 2 ,C 6 H 9 O 4 ,H 2 O contains one 4-aminopyridinium cation, one hydrogen adipate anion and one water molecule. In the hydrogen adipate anion the hydrogen atom of the COOH group is equally disordered (50:50) over two atomic sites. Figure 1 shows the asymmetric unit of the title compound C 5 H 7 N 2 ,C 6 H 9 O 4 ,H 2 O, showing 30% displacement ellipsoid probability and the atom numbering scheme. Cation link the oxygen ends of two adjacent carboxylate of anions. Bonding of the H atom to both pyridine ring N atom and amine group N atom of 4aminopyridinium gives an ion to give the resonance structure.
In the molecular packing the title compound is mainly decided by N-H···O and O-H···O hydrogen bonds. The 4aminopyridinium cations and hydrogen adipate anions are linked through two N-H···O and O-H···O hydrogen bonds (Table 1) forming an infinite molecular chain built from R 4 4 (23) motif. The adjacent lattice water molecules in the crystal is linked through O1S-H2S···O1 hydrogen bond forming an infinite water chain extending along the [0 1 0] direction and the water chains connects the adjacent anionic-cationic chain building up a three dimensional network thus stabilizing the crystalline solid. The hydrogen bonded network is shown in Figure 2 Experimental All the reagents used for the preparation of sample are analytical grade and the solutions are prepared using pure deionized water. Solutions of 4 aminopyridine and adipic acid in water (20 ml) each are mixed in molar ratio of one isto two. The solution was uniformly stirred for 30 min and heated at 303 K for 2 h. The resulting solution was allowed to cool slowly to room temperature. Colorless crystals were obtained by slow evaporation after a period of two weeks.

Refinement
The hydrogen atom of the carboxyl group, which is disordered over two sites with equal occupancy, was located in a difference electron density map and allowed to ride on the parent O atom with d(O-H) = 0.82 Å and U iso (H) = 1.5 U eq (O).
The water H atoms and the H atoms bonded to N atoms were isotropically refined with distance restraints of d 1.36 (4)Å. The carbon H atoms were positioned geometrically and refined using a riding model with C-H = 0.93-0.97 Å and with U iso (H) = 1.2U eq (C) or 1.5U eq (C) for methyl groups.

Figure 1
The asymmetric unit of the title compound showing 30% probability displacement ellipsoids and the atomic numbering.  The crystal packing of the title compound, viewed approximately down b axis. Hydrogen bonds are shown as dashed lines.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (