2-Amino-5-bromopyridinium 3-carboxyprop-2-enoate

In the title salt, C5H6BrN2 +·C4H3O4 −, the 2-amino-5-bromopyridinium cation and hydrogen maleate anion are planar, with maximum deviations from their mean planes of 0.016 (1) and 0.039 (1) Å, respectively. An intramolecular O—H⋯O hydrogen bond generates an S(7) ring motif in the anion. In the crystal, 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—H⋯O hydrogen bonds, forming an R 2 2(8) ring motif. The motifs are linked into a two-dimensional network parallel to (011) by N—H⋯O and C—H⋯O hydrogen bonds.

In the title salt, C 5 H 6 BrN 2 + ÁC 4 H 3 O 4 À , the 2-amino-5-bromopyridinium cation and hydrogen maleate anion are planar, with maximum deviations from their mean planes of 0.016 (1) and 0.039 (1) Å , respectively. An intramolecular O-HÁ Á ÁO hydrogen bond generates an S(7) ring motif in the anion. In the crystal, 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 motifs are linked into a two-dimensional network parallel to (011) by N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds.
They are often involved in hydrogen-bonding interactions (Jeffrey & Saenger, 1991;Jeffrey, 1997;Scheiner, 1997). Maleic acid, the Z isomer of butenedioic acid, has been used as a simple building block in supramolecular architectures in two and three dimensions (Bowes et al., 2003;Jin et al., 2003). The maleic acid anion can exist in the fully deprotonated form or as hydrogen maleate with one of the carboxyl groups protonated (Lah & Leban, 2003). Several singly dissociated maleate salts are reported in the Cambridge Structural Database (Version 5.29; Allen, 2002). Since our aim is to study some interesting hydrogen-bonding interactions, the crystal structure of the title salt is presented here.

Experimental
A hot methanol solution (20 ml) of 2-amino-5-bromopyridine (43 mg, Aldrich) and maleic acid (29 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 and H2N2 were located in a difference Fourier map and were refined freely [N-H= 0.82 (2)

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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.