2-Amino-5-bromo-pyridinium 4-carb-oxy-butano-ate.

In the title salt, C(5)H(6)BrN(2) (+)·C(5)H(7)O(4) (-), the 2-amino-5-bromo-pyridinium cation is essentially planar, with a maximum deviation of 0.005 (3) Å. In the crystal structure, the proton-ated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl-ate O atoms of the anion via a pair of N-H⋯O hydrogen bonds, forming an R(2) (2)(8) ring motif. The ion pairs are further connected via O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds, forming a two-dimensional network parallel to the bc plane. In the network, the hydrogen glutarate (4-carb-oxy-butano-ate) anions self-assemble through O-H⋯O hydrogen bonds, forming a supra-molecular chain along the c axis.

In the title salt, C 5 H 6 BrN 2 + ÁC 5 H 7 O 4 À , the 2-amino-5-bromopyridinium cation is essentially planar, with a maximum deviation of 0.005 (3) Å . In the crystal structure, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxylate O atoms of the anion via a pair of N-HÁ Á ÁO hydrogen bonds, forming an R 2 2 (8) ring motif. The ion pairs are further connected via O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, forming a two-dimensional network parallel to the bc plane. In the network, the hydrogen glutarate (4-carboxybutanoate) anions self-assemble through O-HÁ Á ÁO hydrogen bonds, forming a supramolecular chain along the c axis.

Comment
Weak interactions, such as hydrogen bonding and π-π stacking, have attracted much interest as a result of their significance in chemistry and biology, especially in the field of crystal engineering (Moghimi et al., 2002;Aghabozorg et al., 2005). The design of highly specific solid-state compounds is of considerable significance in organic chemistry due to the important applications of these compounds in the development of new optical, magnetic and electronic systems (Lehn, 1992). The present work is part of a structural study of complexes of 2-amino pyridinium systems with hydrogen-bond donors and we report here the structure of 2-amino-5-bromopyridinium hydrogen glutarate, (I).
The backbone conformation of the hydrogen glutarate anion can be described by the two torsion angles C8-C9-C10-C11 of -178.0 (2)° and C7-C8-C9-C10 of -71.7 (3)°. As evident from the torsion angles, the backbone 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
A hot methanol solution (20 ml) of 2-amino-5-bromopyridine (86 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 crystals of the title compound appeared after a few days.

Refinement
Atoms H1N1, H1N2, H2N2 and H1O4 were located from a difference Fourier map and were refined freely  Fig. 1. The asymmetric unit of the title compound. Displacement ellipsoids are drawn at the 30% probability level.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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.

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