2-Amino-3-carboxypyridinium chloride hemihydrate

The asymmetric unit of the title compound, C6H7N2O2 +·Cl−·0.5H2O, consists of two protonated 2-amino-3-carboxypyridine cations, two chloride anions and one molecule of water. The crystal packing can be described as alternating layers of cations and anions parallel to (110), which are linked together by Ow—H⋯Cl interactions. In the crystal, four types of classical hydrogen bonds are observed, viz. cation–anion (O—H⋯Cl and N—H⋯Cl), cation–cation (N—H⋯O), cation–water (N—H⋯Ow) and water–anion (Ow—H⋯Cl), resulting in the formation of an infinite three-dimensional network.

The asymmetric unit of the title compound, C 6 H 7 N 2 O 2 + Á-Cl À Á0.5H 2 O, consists of two protonated 2-amino-3-carboxypyridine cations, two chloride anions and one molecule of water. The crystal packing can be described as alternating layers of cations and anions parallel to (110), which are linked together by O w -HÁ Á ÁCl interactions. In the crystal, four types of classical hydrogen bonds are observed, viz. cation-anion (O-HÁ Á ÁCl and N-HÁ Á ÁCl), cation-cation (N-HÁ Á ÁO), cation-water (N-HÁ Á ÁO w ) and water-anion (O w -HÁ Á ÁCl), resulting in the formation of an infinite three-dimensional network.
We are grateful to all personel of the LCATM laboratory, Université Oum El Bouaghi, Algé rie for their assistance. Thanks are due to MESRS and ANDRU (Ministé re de l'Enseignement Supé rieur et de la Recherche Scientifique et l'Agence Nationale pour le Dé veloppement de la Recherche Universitaire (ANDRU) -Algé rie) via the PNR programme for financial support.  (Bouacida, 2008;Kickelbick, 2007;Mitzi et al., 1998). Hybrid structures including substituted pyridines organic units have drawn increasing attention due to their potential applications in biological and industrial fields (Asaji et al., 2007;Lynch & Jones, 2004), nitrogen in the pyridine ring has a lone pair of electrons which is not delocalized with the aromatic π-electron system and is easily available for protonation (Berrah et al., 2011a). In the presence of a carboxylic acid substituent, they are recognized as efficient N-O donors exhibiting diverse mode of coordination (Beatty, 2003;Sengupta et al., 2001). Their fascinating structures are rich in H-bonds wich have a potential importance in crystal stability (Berrah et al., 2011a,b,c;Akriche & Rzaigui, 2007).
In continuation of our search to enrich the varieties in such kinds of hybrid compounds and to investigate the influence of hydrogen bonds on the structural features, we report here the synthesis and crystal structure of 2-amino-3-carboxypyridinium chloride hemi hydrate, (I).
The asymmetric unit in this compound consists of two protonated, "2-amino-3-carboxypyridine", amino acids cations (A and B), two chloride anions and one molecule of water. The molecular geometry and the atom-numbering scheme of (I) are shown in Fig. 1. Bond distances and angles observed in the different entities, present no unusual features and are consistent with those reported previously (Berrah et al., 2011b). The crystal packing can be described as alternating layers parallel to (110)

Experimental
The title compound was synthesized by reacting 3-amino-pyridine-2-carboxylic acid (3 mmol) with InCl 3 (1 mmol)in an aqueous solution of hydrochloric acid. The solutions were slowly evaporated to dryness for a couple of weeks. Some colorless crystals were carefully isolated under polarizing microscope for analysis by X-ray diffraction.

Refinement
The H atoms were localized on Fourier maps but introduced in calculated positions and treated as riding on their parent atoms (C, N or O) with C-H = 0.93 Å, O-H = 0.82 Å and N-H = 0.86 Å with U iso (H) = 1.2 U eq (C or N) and U iso (H) = 1.5 U eq (O). H1W and H2W were located in a difference Fourier map and refined isotropically with U iso (H) = 1.5U eq (O).

Figure 1
The asymmetric unit of (I) with the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.    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.