6-Amino-9H-purine-1,7-diium bis(4-methylbenzenesulfonate) monohydrate

The asymmetric unit of the title compound, C5H7N5 2+·2C7H7O3S−·H2O, consists of one diprotonated adeninium cation, two p-toluenesulfonic acid anions and one water molecule. In the crystal, the cations and anions are connected through N—H⋯O hydrogen bonds forming R 2 2(8) and R 2 2(9) graph-set motifs. The solvent water molecule links cations and anions through O—H⋯O and N—H⋯O hydrogen bonds, generating a two-dimensional layer parallel to (10).

The asymmetric unit of the title compound, C 5 H 7 N 5 2+ Á-2C 7 H 7 O 3 S À ÁH 2 O, consists of one diprotonated adeninium cation, two p-toluenesulfonic acid anions and one water molecule. In the crystal, the cations and anions are connected through N-HÁ Á ÁO hydrogen bonds forming R 2 2 (8) and R 2 2 (9) graph-set motifs. The solvent water molecule links cations and anions through O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds, generating a two-dimensional layer parallel to (101).

Comment
Purin and its derivatives, as one kind of important nucleobase compounds, are essential for understanding many mechanisms of basic importance in the biological process (Xing et al., 2008), and belongs to a group of cytokinin-derived compounds which are indispensable for plant growth. The concept of the acyclic nucleoside phosphonate (ANPs) has been used to design chain terminators for antiviral and therapy proved to be valid (Barral et al., 2006) (Sridhar et al., 2009).
In the title compound, C 5 H 7 N 5 2+ .2C 7 H 7 SO 3 -.H 2 O, the asymmetric unit contains one diprotonated adeninium cation, two p-toluenesulfonic acid anions and one water molecule. The two anions are connected to the purin molecule through N-H···O hydrogen bonds building R 2 2 (8) and R 2 2 (9) graph set motifs (Table 1, Fig.1) (Etter, 1990;Bernstein et al., 1995) . In the same asymmetric unit, the water molecule is connected through O-H···O hydrogen bond to one of the p-toluenesulfonic acid (Table 1 Table 1).
In the 9H-purin-6-amine molecule, all atoms are coplanar, the dihedral angles between the plane of the 9H-purin-6-amine and the benzene rings of the p-toluenesulfonate anions are 87.78 (5)° and 87.15 (5)°, respectively, indicating that the 9Hpurin-6-amine is almost perpendicular to the two benzene rings.

Experimental
A mixture of purin-6-amine (10.0 mmol) and toluene sulfonic acid (20.0 mmol) was dissolved in ethanol (40 ml) in batches over a period of 2 h under reflux, heating was continued for 1 h. The mixture was cooled to room temperature and separated, the solvent of the organic phase was removed and the residue recrystallized with ethyl acetate. Yellow crystals of the title compound suitable for X-ray diffraction analysis were obtained after several days. Yield 77.3%.

Refinement
The water H atoms were located in a difference Fourier map but were included in fixed positions in riding-model approx-  6-Amino-9H-purine-1,7-diium bis(4-methylbenzenesulfonate) monohydrate

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 > σ(F 2 ) is used only for calculating Rfactors(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.