Crystal structure, hydrogen bonding and Hirshfeld surface analysis of 2-amino-4-methoxy-6-methylpyrimidinium 4-chlorobenzoate

In the crystal structure of the title compound, C6H10N3O+·C7H4ClO2−, the pyrimidine N atom of the cation is hydrogen-bonded to the 4-chlorobenzoate anion through a pair of N—H⋯Ocarboxyl hydrogen bonds, forming an (8) ring motif which is linked through centrosymmetric (8) ring motifs, forming a pseudotetrameric DDAA array.

In the crystal structure of the title salt, C 6 H 10 N 3 O + ÁC 7 H 4 ClO 2 À , the dihedral angle between the pyrimidine ring of the 2-amino-4-methoxy-6-methylpyrimidine cation and the the benzene ring of the 2-chlorobenzoate anion is 2.2 (1) . In the anion, the benzene ring forms a dihedral angle of 8.5 (2) with the carboxyl group. The pyrimidine N atom of the cation is protonated and the methoxy substituent is essentially coplanar with the parent ring. The protonated N atom and the N atom of the 2-amino group are hydrogen bonded to the 4-chlorobenzoate anion through a pair of N-HÁ Á ÁO carboxyl hydrogen bonds, forming an R 2 2 (8) ring motif linked through a centrosymmetric R 2 4 (8) ring motif, resulting in a pseudotetrameric DDAA array. These units are linked through intermolecular methoxy C-HÁ Á ÁCl hydrogen bonds into ribbon-like chains extending along the c-axis direction. The crystal structure also featuresstacking interactions between the rings in the cation and anion [minimum ring centroid separation = 3.7707 (12) Å ].

Chemical context
Pyrimidine and aminopyrimidine derivatives are biologically important compounds and they occur in nature as components of nucleic acids such as cytosine, uracil and thymine. Pyrimidine derivatives are also important molecules in biology and have many applications in the areas of 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). In order to study the hydrogen-bonding interactions, the title compound, the 2-amino-4-methoxy-6methylpyrimidinium salt of 4-chlorobenzoate, C 6 H 10 N 3 O + ÁC 7 H 4 ClO 2 À , was synthesized and its structure, hydrogen-bonding and Hirshfeld surface analysis are reported herein. ISSN 2056-9890

Structural commentary
The asymmetric unit of the title compound contains a 2-amino-4-methoxy-6-methylpyrimidinium cation and a 4-chlorobenzoate anion ( Fig. 1), which are essentially coplanar, with a dihedral angle between the ring systems of the two species of 2.2 (1) . In the cation, one of the pyrimidine nitrogen atoms (N1) is protonated and this is reflected in an increase in bond angle at N1 [C11-N1-C13 = 120.53 (17) ], when compared with that at the unprotonated atom (N3) [C9-N3-C13 = 116.32 (18) ] and the corresponding angle of 116.01 (18) in neutral 2-amino-4-methoxy-6-methylpyrimidine (Glidewell et al., 2003). The methoxy substituent group at C9 of the cation is essentially coplanar with the ring, the N3-C9-O3-C8 torsion angle being À2.9 (3) . The bond lengths and angles are normal for the carboxylate group of a 4-chlorobenzoate anion, and the benzene ring forms a dihedral angle of 8.5 (2) with the carboxyl group.

Figure 2
Hydrogen bonding in the structure of the title compound showing the R 2 2 (8) and centrosymmetric R 2 4 (8) ring motifs and C-HÁ Á ÁCl extensions. Dashed lines indicate the hydrogen bonds.

Figure 1
The asymmetric unit of the the title compound with atom labels, showing non-hydrogen atoms as 30% probability displacement ellipsoids. Interspecies hydrogen bonds are shown as dashed lines.

Figure 5
Two-dimensional fingerprint plots with the relative contributions to the Hirshfeld surface.
After warming for a few minutes over a water bath, the solution was cooled and kept at room temperature. Within a few days, colourless block-shaped crystals suitable for the X-ray analysis were obtained (yield: 65%).

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.  (7) −0.0149 (7)  O2 0.0454 (8) 0.0481 (7) 0.0872 (11) 0.0023 (6) 0.0242 (7) −0.0098 (7)  C1 0.0404 (9) 0.0449 (10) 0.0527 (11) 0.0003 (7) 0.0141 (8) −0.0010 (8)  C2 0.0406 (9) 0.0447 (9) 0.0424 (10) 0.0005 (7) 0.0149 (8) 0.0012 (7)