2-(Carboxymethyl)imidazo[1,2-a]pyridin-1-ium chloride

In the crystal structure of the title salt, C9H9N2O2 +·Cl−, the cations and anions are linked into chains parallel to [021] by O—H⋯Cl and N—H⋯Cl hydrogen bonds.

In the crystal structure of the title salt, C 9 H 9 N 2 O 2 + ÁCl À , the cations and anions are linked into chains parallel to [021] by O-HÁ Á ÁCl and N-HÁ Á ÁCl hydrogen bonds.

Wen-Yu Yin Comment
Derivatives of imidazole have received great attention for their applications in the field of biology (Catalano et al., 2007;Poul et al., 2007;Takagaki et al., 2012;). The most pervasive is the amino acid histidine, which has an imidazole sidechain (Feng et al., 2012;Samantaray et al., 2007;). In recent years, many derivatives have been used as antifungal agents and bone resorption inhibitors (Keppler et al., 1987;Saha et al., 2012;). As illustrated in Fig. 1, the title compound is composed of one imidazo[1,2-a]pyridin-2-acetic acid cation and a Clanion. The acetic acid group is nearly coplanar with the heterocyele ring with the dihedral angle of 4°. The N2 atom is protonated with N2···H distance of 0.89 (3) Å.

Experimental
To a ethanol solution of 2-aminopyridine (7.21 g, 0.0766 mol) under nitrogen was added ethyl 4-chloroacetoacetate (6 g, 0.0365 mol). The mixture was refluxed for 2 h before concentrated to dryness. The residue was dissolved in 80 ml of purified water and extracted with ethyl acetate. The organic phase was concentrated to give a black oily consistency. 30% KOH (153 ml) was added and stirred for 3 h at 40 o C. The crystals will form after adding concentrated HCl.

Refinement
Carbon-bond H atoms were positioned geometrically (C-H = 0.93 Å for phenyl group, C-H = 0.93 Å for imidazole group), and were included in the refinement in the riding mode approximation, with U iso (H) = 1.2U eq (C) for imidazole group and phenyl group. H atoms bound to O and N atoms were located in a difference Fourier map.

Figure 2
The packing of the title compound. Hydrogen bonds are shown as dashed lines. All H attached to carbon atoms were omitted for clarity.  Three dimensional strucure viewed along the a axis. Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites H atoms treated by a mixture of independent and constrained refinement w = 1/[σ 2 (F o 2 ) + (0.0102P) 2 + 1.0216P] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.19 e Å −3 Δρ min = −0.20 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.