2-Aminopyrimidinium dihydrogen phosphate monohydrate

In the title compound, C4H6N3 +·H2O4P−·H2O, the pyrimidinium ring is essentially planar, with an r.m.s. deviation of 0.0016 Å. In the structure, pairs of symmetry-related anions are connected into centrosymmetric clusters via strong O—H⋯O hydrogen bonds forming six-membered rings with an R 2 2(6) motif. These clusters are interconnected via water molecules through OW—H⋯O hydrogen bonds, building an infinite layer parallel to the ab plane. Moreover, infinite chains of 2-aminopyrimidinium cations spread along the a-axis direction. These chains are connected to the inorganic layer through N—H⋯O, C—H⋯O and C—H⋯N hydrogen bonds, which, together with electrostatic and van der Waals interactions, contribute to the cohesion and stability of the network in the crystal structure.

In the title compound, C 4 H 6 N 3 + ÁH 2 O 4 P À ÁH 2 O, the pyrimidinium ring is essentially planar, with an r.m.s. deviation of 0.0016 Å . In the structure, pairs of symmetry-related anions are connected into centrosymmetric clusters via strong O-HÁ Á ÁO hydrogen bonds forming six-membered rings with an R 2 2 (6) motif. These clusters are interconnected via water molecules through OW-HÁ Á ÁO hydrogen bonds, building an infinite layer parallel to the ab plane. Moreover, infinite chains of 2-aminopyrimidinium cations spread along the a-axis direction. These chains are connected to the inorganic layer through N-HÁ Á ÁO, C-HÁ Á ÁO and C-HÁ Á ÁN hydrogen bonds, which, together with electrostatic and van der Waals interactions, contribute to the cohesion and stability of the network in the crystal structure.
In addition, pyrimidine derivatives possess considerable biological activity and have been widely used in medicinal applications as antiviral agents (Gueiffier et al., 1996), antifungal agents (Rival et al., 1991). Moreover, imidazolidinonyl aminopyrimidine compounds have been investigated for the treatment of cancer (Li et al., 2009). In order to search for new materials for these applications, we have attempted to combine pyrimidine derivatives with phosphate species. In this paper we report the preparation and the crystal structure of the title compound, (I).
The asymmetric unit of (I) contains a H 2 PO 4 anion, a 2-aminopyrimidinium cation and a water molecule (Fig. 1). The pyrimidinium ring is essentially planar with an rms deviation of 0.0016 Å. The interatomic bond lengths and angles in (I) do not show significant deviation from those reported in related 2-aminopyrimidinium salts (Narayana, et al., 2008;Cheng, et al., 2010).
In the structure, pairs of symmetry-related anions are connected into centrosymmetric clusters via strong O-H···O hydrogen bonds forming six-membred rings which may be described as R 2 2 (6) motif in the graph-set notation (Bernstein et al., 1995). These clusters are interconnected via water molecules through OW-H···O hydrogen bonds to build an infinite layer parallel to the ab plane. Moreover, infinite chains of 2-aminopyrimidinium cations spread along the a direction. These chains are connected to the inorganic layer through H-bonds: N-H···O, C-H···O and C-H···N (Tab. 1 & Fig. 2).

Experimental
A small quantity of H 3 PO 4 (3 mmol) was added dropwise to a solution of 2-aminopyrimidine (3 mmol in 20 ml water).
A precipitate was formed which was dissolved in water (20 ml) and the solution was allowed to evaporate slowly at room temperature until the formation of colorless prismatic crystals with dimensions suitable for a crystallographic study.

Refinement
All H atoms were located in difference Fourier maps and were allowed to refine with isotropic displacement parameters  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.