Crystal structure and Hirshfeld surface analysis of 2-amino-4-methoxy-6-methylpyrimidinium 2-hydroxybenzoate

Tetrameric associations of two cations and two anions occur, being linked by N—H⋯O hydrogen bonds.

In the title molecular salt, C 6 H 10 N 3 O + ÁC 7 H 5 O 3 À , the cation is protonated at the N atom lying between the amine and methyl substituents and the dihedral angle between the carboxyl group and its attached ring in the anion is 4.0 (2) . The anion features an intramolecular O-HÁ Á ÁO hydrogen bond, which closes an S(6) ring. The cation and anion are linked by two N-HÁ Á ÁO hydrogen bonds [R 2 2 (8) motif] to generate an ion pair in which the dihedral angle between the aromatic rings is 8.34 (9) . Crystal symmetry relates two ion pairs bridged by further N-HÁ Á ÁO hydrogen bonds into a tetrameric DDAA array. The tetramers are linked by pairs of C-HÁ Á ÁO hydrogen bonds to generate [100] chains. Hirshfeld surface and fingerprint plot analyses are presented.

chemical context
Pyrimidine and aminopyrimidine derivatives have many applications as pesticides and pharmaceutical agents (Condon et al., 1993). For example, imazosulfuron, ethirmol and mepanipyrim have been commercialized as agrochemicals (Maeno et al., 1990). Pyrimidine derivatives have also been developed as antiviral agents, such as AZT, which is the most widely-used anti-AIDS drug (Gilchrist, 1997). Hydrogen bonding plays a vital role in molecular recognition. Supramolecular chemistry plays a pivotal role in biological systems and in artificial systems. It refers to the specific interaction between two or more motifs through non-covalent interactions such as hydrogen bonding, hydrophobic forces, van der Waals forces,interactions etc. The generating of supramolecular architectures is correlated to the positions and properties of the active groups in molecules (Desiraju et al., 1989;Steiner et al., 2002) As part of our studies in these areas, the synthesis and structure of the title molecular salt, (I), is presented here.

Figure 1
The asymmetric unit of (I), with 50% probability displacement ellipsoids.

Synthesis and crystallization
The title compound was synthesized by mixing hot methanolic solutions (20 ml) of 2-amino-4-methoxy-6-methylpyrimidine (0.139 mg) and 2-hydroxybenzoic acid (0.156 mg) in a 1:1 molar ratio. The mixed solutions were warmed few minutes over a waterbath and then cooled and kept at room temperature for slow evaporation. After a few days, colourless block-shaped crystals of (I) were obtained (yield = 65%).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The hydrogen atoms were positioned geometrically (N-H = 0.86, O-H = 0.82 and C-H = 0.96 or 0.93 Å ) and were refined using a riding model, with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C). A rotating-group model was used for the methyl group.  Computer programs: APEX2 and SAINT (Bruker, 2004), SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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.