2-Aminopyrimidinium hydrogen chloranilate monohydrate

In the title compound, C4H6N3 +·C6HCl2O4 −·H2O, anions, cations and water molecules are linked by intermolecular O—H⋯O, O—H⋯N and N—H⋯O hydrogen bonds into one-dimensional tapes along [111]. These tapes are further linked by weak Cl⋯Cl interactions [Cl⋯Cl = 3.394 (2) Å], forming sheets parallel to the (10) plane.


Comment
Chloranilic acid (CA) can be regarded as a strong organic acid (pK a1 = 1.38; pK a2 = 2.98) which can release its two hydroxyl protons easily. For this reason, CA is often used as a bridge ligand in the synthesis of metal coordination complexes (Kawata et al., 1994;Kawata et al., 1998;Abrahams et al., 2002;Cueto et al., 1992;Min et al., 2006;Min et al., 2007) or used as a cocrystal agent in the construction of supramolecular structure based on hydrogen-bonds (Gotoh et al., 2006(Gotoh et al., , 2007a(Gotoh et al., , 2007b(Gotoh et al., and 2007cMurata et al., 2007;Gaballa et al., 2008;Jia et al., 2008). As part of our continuing studies on the synthesis of co-crystal or organic salts involved CA (Meng & Qian, 2006), we report here the crystal structure of the title compound (I) which was obtained by mixing equivalent amount of CA and 2-aminopyrimidine (2-APy) in 95% methanol solution at room temperature.
In (I), one of the CA hydroxyl protons is transferred to a pyrimidine N atom, forming a 1:1 organic adduct with one water molecule being incorporated into the crystal lattice ( Fig. 1). According to the definitions of co-crystal and organic salt proposed by Aakeröy and Salmon (2005), complex (I) can be considered as an organic salt. The bond lengths and bonds angles in the CAanion are comparable with those from some analogues (Wang & Wei, 2005;Yang, 2007). In the 2-APy + cation, the angles of C7-N1-C8 and C7-N2-C10 [116.5 (1)° and 122.2 (1)°, respectively] are both consistent with the magnitude of C-N-C angles in unprotonated and protonated pyridine molecules [116.3 (16)° and 122.4 (16)°, respectively] (Allen et al., 1987;Allen, 2002). All other geomtric parameters in the structure are as expected.

Experimental
All the reagents and solvents were used as obtained without further purification. Equivalent molar amount of chloranilic acid (1 mmol, 210 mg) and 2-aminopyimidine (1 mmol, 9.5 mg) were dissolved in 95% methanol (20 ml). The mixture was stirred for half an hour at ambient temperature and then filtered. The resulting red solution was kept in air for two week.
Plate-like crystals of (I) suitable for single-crystal X-ray diffraction analysis were grown at the bottom of the vessel by slow evaporation of the solution.

Refinement
H atoms bonded to C atoms were located in difference maps and subsequently treated as riding modes, with C-H=0.93 Å and U iso (H) = 1.2U eq (C). H atoms bonded to N and O atoms were also found in difference maps, with the constraints

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.