2-Amino-3-carboxypyridinium perchlorate

The asymmetric unit includes two crystallographically independent equivalents of the title salt, C6H7N2O2 +·ClO4 −. The cations and anions form separate layers alternating along the c axis, which are linked by N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds into a two-dimensional network parallel to (100). Further C—H⋯O contacts connect these layers, forming a three-dimensional network, in which R 4 4(20) rings and C 2 2(11) infinite chains can be identified.

The asymmetric unit includes two crystallographically independent equivalents of the title salt, C 6 H 7 N 2 O 2 + ÁClO 4 À . The cations and anions form separate layers alternating along the c axis, which are linked by N-HÁ Á ÁO, O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds into a two-dimensional network parallel to (100). Further C-HÁ Á ÁO contacts connect these layers, forming a three-dimensional network, in which R 4 4 (20) rings and C 2 2 (11) infinite chains can be identified.

Experimental
Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT; program(s) used to solve structure: SIR2002 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: WinGX (Farrugia, 1999 As a continuation of the systematic studies on synthesis and structural characterization of the products of derivatives of nicotinic acid with inorganic acids, and as an attempt to establish a relationship between the nature of the anion and the resulting hydrogen-bonding pattern, we report here the crystal structure of the title compound obtained by reaction between 2-aminonicotinic and perchloric acids. Related compounds obtained with dihydrogen phosphate, sulfate and nitrate anions, have been reported previously (Akriche & Rzaigui 2007;Berrah et al. 2011a,b).
The dimers of 2-aminonicotinium cations are formed via N-H···O h-bonds (NH of the amine group with the O of the carboxylic group). Similar dimers have been also observed in the structures with dihydrogen phosphate and sulfate anions (Akriche & Rzaigui 2007;Berrah et al. 2011a), while cations in the nitrate structure adopt a different configuration (Berrah et al. 2011b).
In the crystal structure, cationic and anionic layers alternate along the c axis and are linked by intermolecular N-H···O, O-H···O and weak C-H···O hydrogen bonds (see table 1) resulting in a two-dimensional network parallel to (100) ( Fig.2). Further C-H···O contacts connect these layers, forming a three-dimensional network in which R 4 4 (20) rings and C 2 2 (11) infinite chains are generated (Etter et al. 1990;Grell et al. 1999).

Experimental
Colourless crystals of compound (I) were grown by slow evaporation of an aquoes solution of 2-amino-pyridine-3-carboxylic acid and perchloric acid in an 1:1 stoichiometric ratio.

Refinement
All H atoms were located in a difference Fourier maps but introduced at calculated positions and treated as riding on their parent atoms (C,N or O) with C-H = 0.93 Å,N-H = 0.88 Å and O-H = 0.82 Å with U iso (H) = 1.2 U eq (C or N) and

Computing details
Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SIR2002 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: WinGX (Farrugia, 1999      where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.34 e Å −3 Δρ min = −0.40 e Å −3 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.