Bis(2-amino-4-methyl-6-oxo-3,6-dihydropyrimidin-1-ium) sulfate monohydrate

In the title hydrated molecular salt, 2C5H8N3O+·SO4 2−·H2O, the components are linked by N—H⋯Os and Ow—H⋯Os (s = sulphate, w = water) hydrogen bonds, generating a layer by a+b+c and 2a−b translations. The cations are arranged nearly in parallel and show displaced π–π stacking centroid–centroid distance = 4.661 (2) Å between adjacent layers.

In the title hydrated molecular salt, 2C 5 H 8 N 3 O + ÁSO 4 2À ÁH 2 O, the components are linked by N-HÁ Á ÁO s and O w -HÁ Á ÁO s (s = sulphate, w = water) hydrogen bonds, generating a layer by a+b+c and 2aÀb translations. The cations are arranged nearly in parallel and show displacedstacking centroid-centroid distance = 4.661 (2) Å between adjacent layers.

Comment
Chemists and physicists of the solid state have shown an increasing interest in the study of oxoanion compounds containing organic cations in recent years owing to their applications in various fields (Vollano et al., 1984;Molloy, 1988). Here, we report the synthesis and the crystal structure of the title compound 2(C 5 H 8 N 3 O), O 4 S, H 2 O. The asymmetric unit of this salt contains two molecules of 2-amino-6-methylpyrimidin-4-(1H)-one, one sulfate anion and one water molecule (Fig. 1). The two independent aromatic cycles of the asymmetric unit are nearly parallel as they form an angle of 5.8°. The shortest distance between non-H atoms of two cations in parallel displaced π-staking is d(O3···N17) = 3.375 (2) Å. When the two cation molecules are viewed along the two centroids, the 6 atom positions of the two cycles appear superposed after a rotation of 60° (Fig. 1). The crystal structure of the title material consists of a network of the different constituents connected by a set of hydrogen bonds (Table 1). Furthermore, in the crystal packing, the two cations are arranged in layers (Fig. 2). The sulfate anion forms the strongest interactions between two parallel layers, as each sulfate moiety interacts with the five cations via seven N-H···O hydrogen bonds. The hydrogen bond network in the cations layer is shown in Fig. 3. The water molecule is acceptor in one N-H···O hydrogen bond and donor in two O -H···O interactions with the sulfate anion and carbonyl group. In the atomic arrangement of the title compound, the sulfate anions are located close to the z=0 plane. Along the a diretion, they are interconnected via a same NH 2 group. In the crystal structure, various graph set motifs (Bernstein et al., 1995) are apparent including R 2 4 (8) and R 3 6 (8) loops (Fig.   4). An examination of Table 2 data shows that the distance values of C3-O3 (1.229 (2) Å) and C13-O13 (1.226 (2) Å) can be attributed as having clear double bond character indicating that the title compound is present as the keto tautomer of the 2-amino-6-methyl-4-pyrimidinol(sheme. 2). This observation agrees with the literature data which show that in polar solvents, the quinonic form is more stable than the phenolic one (Fragoso et al., 2010). The C-N bond distances of the NH 2 groups are C1-N1 (1.315 (2) Å), and C11-N11 (1.318 (2) Å) which are short for C-N single bonds, but still not quite as contracted as one would expect for a fully established C=N double bond. These bond length features are consistent with an imino resonance form as it is commonly found for a C-N single bond involving sp 2 hybridized C and N atoms, (Yang et al., 1995;Grobelny et al., 1995). The S-O bond lengths and the O-S-O bond angles in the sulfate anion are not perfectly equivalent (Das et al., 2009;Norquist et al., 2005), but vary with the environment around the O atoms. In the title compound, the S-O distances are spread between 1.4759 (14) and 1.4949 (16) Å. The O-S-O bond angles range from 108,97 (8) to 110.24 (9)°. All these geometrical parameters indicate relatively little distortion from a regular tetrahedron.

Experimental
Commercial 2-amino-4-hydroxy-6-methylpyrimidine (50 mg, 0.4 mmol) dissolved in ethanol (10 ml) was slowly added under stirring to 0.05 mol of sulfuric acid in 20 ml of water. The obtained solution was left to stand at room temperature.
The slow evaporation of solvent leads to the formation of colourless single crystals of (I), stable in air and suitable for X-supplementary materials sup-2 Acta Cryst. (2014). E70, o747-o748 ray diffraction analysis.

Refinement
The structure was refined with SHELXL97 (Sheldrick, 2008). The coordinates of the H atoms were refined with U iso (H) = 1.2Ueq(X) except for the methyl groups for which U iso (H) was set to 1.5Ueq(X), where X is the parent atom. The C-H distances in the two methyl groups were restraint to be similar (sigma=0.01).     View along the c-axis showing O-H···O and N-H···O hydrogen bonds forming two kinds of 8-membered rings. 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.